TinyGo : fmt package for debugging the machine package

errors.go

// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package fmt

import "errors"

// Errorf formats according to a format specifier and returns the string as a
// value that satisfies error.
//
// If the format specifier includes a %w verb with an error operand,
// the returned error will implement an Unwrap method returning the operand. It is
// invalid to include more than one %w verb or to supply it with an operand
// that does not implement the error interface. The %w verb is otherwise
// a synonym for %v.
func Errorf(format string, a ...any) error {
	p := newPrinter()
	p.wrapErrs = true
	p.doPrintf(format, a)
	s := string(p.buf)
	var err error
	if p.wrappedErr == nil {
		err = errors.New(s)
	} else {
		err = &wrapError{s, p.wrappedErr}
	}
	p.free()
	return err
}

type wrapError struct {
	msg string
	err error
}

func (e *wrapError) Error() string {
	return e.msg
}

func (e *wrapError) Unwrap() error {
	return e.err
}

format.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package fmt

import (
	"strconv"
	"unicode/utf8"
)

const (
	ldigits = "0123456789abcdefx"
	udigits = "0123456789ABCDEFX"
)

const (
	signed   = true
	unsigned = false
)

// flags placed in a separate struct for easy clearing.
type fmtFlags struct {
	widPresent  bool
	precPresent bool
	minus       bool
	plus        bool
	sharp       bool
	space       bool
	zero        bool

	// For the formats %+v %#v, we set the plusV/sharpV flags
	// and clear the plus/sharp flags since %+v and %#v are in effect
	// different, flagless formats set at the top level.
	plusV  bool
	sharpV bool
}

// A fmt is the raw formatter used by Printf etc.
// It prints into a buffer that must be set up separately.
type fmt struct {
	buf *buffer

	fmtFlags

	wid  int // width
	prec int // precision

	// intbuf is large enough to store %b of an int64 with a sign and
	// avoids padding at the end of the struct on 32 bit architectures.
	intbuf [68]byte
}

func (f *fmt) clearflags() {
	f.fmtFlags = fmtFlags{}
}

func (f *fmt) init(buf *buffer) {
	f.buf = buf
	f.clearflags()
}

// writePadding generates n bytes of padding.
func (f *fmt) writePadding(n int) {
	if n <= 0 { // No padding bytes needed.
		return
	}
	buf := *f.buf
	oldLen := len(buf)
	newLen := oldLen + n
	// Make enough room for padding.
	if newLen > cap(buf) {
		buf = make(buffer, cap(buf)*2+n)
		copy(buf, *f.buf)
	}
	// Decide which byte the padding should be filled with.
	padByte := byte(' ')
	if f.zero {
		padByte = byte('0')
	}
	// Fill padding with padByte.
	padding := buf[oldLen:newLen]
	for i := range padding {
		padding[i] = padByte
	}
	*f.buf = buf[:newLen]
}

// pad appends b to f.buf, padded on left (!f.minus) or right (f.minus).
func (f *fmt) pad(b []byte) {
	if !f.widPresent || f.wid == 0 {
		f.buf.write(b)
		return
	}
	width := f.wid - utf8.RuneCount(b)
	if !f.minus {
		// left padding
		f.writePadding(width)
		f.buf.write(b)
	} else {
		// right padding
		f.buf.write(b)
		f.writePadding(width)
	}
}

// padString appends s to f.buf, padded on left (!f.minus) or right (f.minus).
func (f *fmt) padString(s string) {
	if !f.widPresent || f.wid == 0 {
		f.buf.writeString(s)
		return
	}
	width := f.wid - utf8.RuneCountInString(s)
	if !f.minus {
		// left padding
		f.writePadding(width)
		f.buf.writeString(s)
	} else {
		// right padding
		f.buf.writeString(s)
		f.writePadding(width)
	}
}

// fmtBoolean formats a boolean.
func (f *fmt) fmtBoolean(v bool) {
	if v {
		f.padString("true")
	} else {
		f.padString("false")
	}
}

// fmtUnicode formats a uint64 as "U+0078" or with f.sharp set as "U+0078 'x'".
func (f *fmt) fmtUnicode(u uint64) {
	buf := f.intbuf[0:]

	// With default precision set the maximum needed buf length is 18
	// for formatting -1 with %#U ("U+FFFFFFFFFFFFFFFF") which fits
	// into the already allocated intbuf with a capacity of 68 bytes.
	prec := 4
	if f.precPresent && f.prec > 4 {
		prec = f.prec
		// Compute space needed for "U+" , number, " '", character, "'".
		width := 2 + prec + 2 + utf8.UTFMax + 1
		if width > len(buf) {
			buf = make([]byte, width)
		}
	}

	// Format into buf, ending at buf[i]. Formatting numbers is easier right-to-left.
	i := len(buf)

	// For %#U we want to add a space and a quoted character at the end of the buffer.
	if f.sharp && u <= utf8.MaxRune && strconv.IsPrint(rune(u)) {
		i--
		buf[i] = '\''
		i -= utf8.RuneLen(rune(u))
		utf8.EncodeRune(buf[i:], rune(u))
		i--
		buf[i] = '\''
		i--
		buf[i] = ' '
	}
	// Format the Unicode code point u as a hexadecimal number.
	for u >= 16 {
		i--
		buf[i] = udigits[u&0xF]
		prec--
		u >>= 4
	}
	i--
	buf[i] = udigits[u]
	prec--
	// Add zeros in front of the number until requested precision is reached.
	for prec > 0 {
		i--
		buf[i] = '0'
		prec--
	}
	// Add a leading "U+".
	i--
	buf[i] = '+'
	i--
	buf[i] = 'U'

	oldZero := f.zero
	f.zero = false
	f.pad(buf[i:])
	f.zero = oldZero
}

// fmtInteger formats signed and unsigned integers.
func (f *fmt) fmtInteger(u uint64, base int, isSigned bool, verb rune, digits string) {
	negative := isSigned && int64(u) < 0
	if negative {
		u = -u
	}

	buf := f.intbuf[0:]
	// The already allocated f.intbuf with a capacity of 68 bytes
	// is large enough for integer formatting when no precision or width is set.
	if f.widPresent || f.precPresent {
		// Account 3 extra bytes for possible addition of a sign and "0x".
		width := 3 + f.wid + f.prec // wid and prec are always positive.
		if width > len(buf) {
			// We're going to need a bigger boat.
			buf = make([]byte, width)
		}
	}

	// Two ways to ask for extra leading zero digits: %.3d or %03d.
	// If both are specified the f.zero flag is ignored and
	// padding with spaces is used instead.
	prec := 0
	if f.precPresent {
		prec = f.prec
		// Precision of 0 and value of 0 means "print nothing" but padding.
		if prec == 0 && u == 0 {
			oldZero := f.zero
			f.zero = false
			f.writePadding(f.wid)
			f.zero = oldZero
			return
		}
	} else if f.zero && f.widPresent {
		prec = f.wid
		if negative || f.plus || f.space {
			prec-- // leave room for sign
		}
	}

	// Because printing is easier right-to-left: format u into buf, ending at buf[i].
	// We could make things marginally faster by splitting the 32-bit case out
	// into a separate block but it's not worth the duplication, so u has 64 bits.
	i := len(buf)
	// Use constants for the division and modulo for more efficient code.
	// Switch cases ordered by popularity.
	switch base {
	case 10:
		for u >= 10 {
			i--
			next := u / 10
			buf[i] = byte('0' + u - next*10)
			u = next
		}
	case 16:
		for u >= 16 {
			i--
			buf[i] = digits[u&0xF]
			u >>= 4
		}
	case 8:
		for u >= 8 {
			i--
			buf[i] = byte('0' + u&7)
			u >>= 3
		}
	case 2:
		for u >= 2 {
			i--
			buf[i] = byte('0' + u&1)
			u >>= 1
		}
	default:
		panic("fmt: unknown base; can't happen")
	}
	i--
	buf[i] = digits[u]
	for i > 0 && prec > len(buf)-i {
		i--
		buf[i] = '0'
	}

	// Various prefixes: 0x, -, etc.
	if f.sharp {
		switch base {
		case 2:
			// Add a leading 0b.
			i--
			buf[i] = 'b'
			i--
			buf[i] = '0'
		case 8:
			if buf[i] != '0' {
				i--
				buf[i] = '0'
			}
		case 16:
			// Add a leading 0x or 0X.
			i--
			buf[i] = digits[16]
			i--
			buf[i] = '0'
		}
	}
	if verb == 'O' {
		i--
		buf[i] = 'o'
		i--
		buf[i] = '0'
	}

	if negative {
		i--
		buf[i] = '-'
	} else if f.plus {
		i--
		buf[i] = '+'
	} else if f.space {
		i--
		buf[i] = ' '
	}

	// Left padding with zeros has already been handled like precision earlier
	// or the f.zero flag is ignored due to an explicitly set precision.
	oldZero := f.zero
	f.zero = false
	f.pad(buf[i:])
	f.zero = oldZero
}

// truncateString truncates the string s to the specified precision, if present.
func (f *fmt) truncateString(s string) string {
	if f.precPresent {
		n := f.prec
		for i := range s {
			n--
			if n < 0 {
				return s[:i]
			}
		}
	}
	return s
}

// truncate truncates the byte slice b as a string of the specified precision, if present.
func (f *fmt) truncate(b []byte) []byte {
	if f.precPresent {
		n := f.prec
		for i := 0; i < len(b); {
			n--
			if n < 0 {
				return b[:i]
			}
			wid := 1
			if b[i] >= utf8.RuneSelf {
				_, wid = utf8.DecodeRune(b[i:])
			}
			i += wid
		}
	}
	return b
}

// fmtS formats a string.
func (f *fmt) fmtS(s string) {
	s = f.truncateString(s)
	f.padString(s)
}

// fmtBs formats the byte slice b as if it was formatted as string with fmtS.
func (f *fmt) fmtBs(b []byte) {
	b = f.truncate(b)
	f.pad(b)
}

// fmtSbx formats a string or byte slice as a hexadecimal encoding of its bytes.
func (f *fmt) fmtSbx(s string, b []byte, digits string) {
	length := len(b)
	if b == nil {
		// No byte slice present. Assume string s should be encoded.
		length = len(s)
	}
	// Set length to not process more bytes than the precision demands.
	if f.precPresent && f.prec < length {
		length = f.prec
	}
	// Compute width of the encoding taking into account the f.sharp and f.space flag.
	width := 2 * length
	if width > 0 {
		if f.space {
			// Each element encoded by two hexadecimals will get a leading 0x or 0X.
			if f.sharp {
				width *= 2
			}
			// Elements will be separated by a space.
			width += length - 1
		} else if f.sharp {
			// Only a leading 0x or 0X will be added for the whole string.
			width += 2
		}
	} else { // The byte slice or string that should be encoded is empty.
		if f.widPresent {
			f.writePadding(f.wid)
		}
		return
	}
	// Handle padding to the left.
	if f.widPresent && f.wid > width && !f.minus {
		f.writePadding(f.wid - width)
	}
	// Write the encoding directly into the output buffer.
	buf := *f.buf
	if f.sharp {
		// Add leading 0x or 0X.
		buf = append(buf, '0', digits[16])
	}
	var c byte
	for i := 0; i < length; i++ {
		if f.space && i > 0 {
			// Separate elements with a space.
			buf = append(buf, ' ')
			if f.sharp {
				// Add leading 0x or 0X for each element.
				buf = append(buf, '0', digits[16])
			}
		}
		if b != nil {
			c = b[i] // Take a byte from the input byte slice.
		} else {
			c = s[i] // Take a byte from the input string.
		}
		// Encode each byte as two hexadecimal digits.
		buf = append(buf, digits[c>>4], digits[c&0xF])
	}
	*f.buf = buf
	// Handle padding to the right.
	if f.widPresent && f.wid > width && f.minus {
		f.writePadding(f.wid - width)
	}
}

// fmtSx formats a string as a hexadecimal encoding of its bytes.
func (f *fmt) fmtSx(s, digits string) {
	f.fmtSbx(s, nil, digits)
}

// fmtBx formats a byte slice as a hexadecimal encoding of its bytes.
func (f *fmt) fmtBx(b []byte, digits string) {
	f.fmtSbx("", b, digits)
}

// fmtQ formats a string as a double-quoted, escaped Go string constant.
// If f.sharp is set a raw (backquoted) string may be returned instead
// if the string does not contain any control characters other than tab.
func (f *fmt) fmtQ(s string) {
	s = f.truncateString(s)
	if f.sharp && strconv.CanBackquote(s) {
		f.padString("`" + s + "`")
		return
	}
	buf := f.intbuf[:0]
	if f.plus {
		f.pad(strconv.AppendQuoteToASCII(buf, s))
	} else {
		f.pad(strconv.AppendQuote(buf, s))
	}
}

// fmtC formats an integer as a Unicode character.
// If the character is not valid Unicode, it will print '\ufffd'.
func (f *fmt) fmtC(c uint64) {
	r := rune(c)
	if c > utf8.MaxRune {
		r = utf8.RuneError
	}
	buf := f.intbuf[:0]
	w := utf8.EncodeRune(buf[:utf8.UTFMax], r)
	f.pad(buf[:w])
}

// fmtQc formats an integer as a single-quoted, escaped Go character constant.
// If the character is not valid Unicode, it will print '\ufffd'.
func (f *fmt) fmtQc(c uint64) {
	r := rune(c)
	if c > utf8.MaxRune {
		r = utf8.RuneError
	}
	buf := f.intbuf[:0]
	if f.plus {
		f.pad(strconv.AppendQuoteRuneToASCII(buf, r))
	} else {
		f.pad(strconv.AppendQuoteRune(buf, r))
	}
}

// fmtFloat formats a float64. It assumes that verb is a valid format specifier
// for strconv.AppendFloat and therefore fits into a byte.
func (f *fmt) fmtFloat(v float64, size int, verb rune, prec int) {
	// Explicit precision in format specifier overrules default precision.
	if f.precPresent {
		prec = f.prec
	}
	// Format number, reserving space for leading + sign if needed.
	num := strconv.AppendFloat(f.intbuf[:1], v, byte(verb), prec, size)
	if num[1] == '-' || num[1] == '+' {
		num = num[1:]
	} else {
		num[0] = '+'
	}
	// f.space means to add a leading space instead of a "+" sign unless
	// the sign is explicitly asked for by f.plus.
	if f.space && num[0] == '+' && !f.plus {
		num[0] = ' '
	}
	// Special handling for infinities and NaN,
	// which don't look like a number so shouldn't be padded with zeros.
	if num[1] == 'I' || num[1] == 'N' {
		oldZero := f.zero
		f.zero = false
		// Remove sign before NaN if not asked for.
		if num[1] == 'N' && !f.space && !f.plus {
			num = num[1:]
		}
		f.pad(num)
		f.zero = oldZero
		return
	}
	// The sharp flag forces printing a decimal point for non-binary formats
	// and retains trailing zeros, which we may need to restore.
	if f.sharp && verb != 'b' {
		digits := 0
		switch verb {
		case 'v', 'g', 'G', 'x':
			digits = prec
			// If no precision is set explicitly use a precision of 6.
			if digits == -1 {
				digits = 6
			}
		}

		// Buffer pre-allocated with enough room for
		// exponent notations of the form "e+123" or "p-1023".
		var tailBuf [6]byte
		tail := tailBuf[:0]

		hasDecimalPoint := false
		sawNonzeroDigit := false
		// Starting from i = 1 to skip sign at num[0].
		for i := 1; i < len(num); i++ {
			switch num[i] {
			case '.':
				hasDecimalPoint = true
			case 'p', 'P':
				tail = append(tail, num[i:]...)
				num = num[:i]
			case 'e', 'E':
				if verb != 'x' && verb != 'X' {
					tail = append(tail, num[i:]...)
					num = num[:i]
					break
				}
				fallthrough
			default:
				if num[i] != '0' {
					sawNonzeroDigit = true
				}
				// Count significant digits after the first non-zero digit.
				if sawNonzeroDigit {
					digits--
				}
			}
		}
		if !hasDecimalPoint {
			// Leading digit 0 should contribute once to digits.
			if len(num) == 2 && num[1] == '0' {
				digits--
			}
			num = append(num, '.')
		}
		for digits > 0 {
			num = append(num, '0')
			digits--
		}
		num = append(num, tail...)
	}
	// We want a sign if asked for and if the sign is not positive.
	if f.plus || num[0] != '+' {
		// If we're zero padding to the left we want the sign before the leading zeros.
		// Achieve this by writing the sign out and then padding the unsigned number.
		if f.zero && f.widPresent && f.wid > len(num) {
			f.buf.writeByte(num[0])
			f.writePadding(f.wid - len(num))
			f.buf.write(num[1:])
			return
		}
		f.pad(num)
		return
	}
	// No sign to show and the number is positive; just print the unsigned number.
	f.pad(num[1:])
}

print.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package fmt

import (
	"internal/fmtsort"
	"io"
	"reflect"
	"sync"
	"unicode/utf8"
)

// Strings for use with buffer.WriteString.
// This is less overhead than using buffer.Write with byte arrays.
const (
	commaSpaceString  = ", "
	nilAngleString    = "<nil>"
	nilParenString    = "(nil)"
	nilString         = "nil"
	mapString         = "map["
	percentBangString = "%!"
	missingString     = "(MISSING)"
	badIndexString    = "(BADINDEX)"
	panicString       = "(PANIC="
	extraString       = "%!(EXTRA "
	badWidthString    = "%!(BADWIDTH)"
	badPrecString     = "%!(BADPREC)"
	noVerbString      = "%!(NOVERB)"
	invReflectString  = "<invalid reflect.Value>"
)

// State represents the printer state passed to custom formatters.
// It provides access to the io.Writer interface plus information about
// the flags and options for the operand's format specifier.
type State interface {
	// Write is the function to call to emit formatted output to be printed.
	Write(b []byte) (n int, err error)
	// Width returns the value of the width option and whether it has been set.
	Width() (wid int, ok bool)
	// Precision returns the value of the precision option and whether it has been set.
	Precision() (prec int, ok bool)

	// Flag reports whether the flag c, a character, has been set.
	Flag(c int) bool
}

// Formatter is implemented by any value that has a Format method.
// The implementation controls how State and rune are interpreted,
// and may call Sprint(f) or Fprint(f) etc. to generate its output.
type Formatter interface {
	Format(f State, verb rune)
}

// Stringer is implemented by any value that has a String method,
// which defines the ``native'' format for that value.
// The String method is used to print values passed as an operand
// to any format that accepts a string or to an unformatted printer
// such as Print.
type Stringer interface {
	String() string
}

// GoStringer is implemented by any value that has a GoString method,
// which defines the Go syntax for that value.
// The GoString method is used to print values passed as an operand
// to a %#v format.
type GoStringer interface {
	GoString() string
}

// Use simple []byte instead of bytes.Buffer to avoid large dependency.
type buffer []byte

func (b *buffer) write(p []byte) {
	*b = append(*b, p...)
}

func (b *buffer) writeString(s string) {
	*b = append(*b, s...)
}

func (b *buffer) writeByte(c byte) {
	*b = append(*b, c)
}

func (bp *buffer) writeRune(r rune) {
	if r < utf8.RuneSelf {
		*bp = append(*bp, byte(r))
		return
	}

	b := *bp
	n := len(b)
	for n+utf8.UTFMax > cap(b) {
		b = append(b, 0)
	}
	w := utf8.EncodeRune(b[n:n+utf8.UTFMax], r)
	*bp = b[:n+w]
}

// pp is used to store a printer's state and is reused with sync.Pool to avoid allocations.
type pp struct {
	buf buffer

	// arg holds the current item, as an interface{}.
	arg any

	// value is used instead of arg for reflect values.
	value reflect.Value

	// fmt is used to format basic items such as integers or strings.
	fmt fmt

	// reordered records whether the format string used argument reordering.
	reordered bool
	// goodArgNum records whether the most recent reordering directive was valid.
	goodArgNum bool
	// panicking is set by catchPanic to avoid infinite panic, recover, panic, ... recursion.
	panicking bool
	// erroring is set when printing an error string to guard against calling handleMethods.
	erroring bool
	// wrapErrs is set when the format string may contain a %w verb.
	wrapErrs bool
	// wrappedErr records the target of the %w verb.
	wrappedErr error
}

var ppFree = sync.Pool{
	New: func() any { return new(pp) },
}

// newPrinter allocates a new pp struct or grabs a cached one.
func newPrinter() *pp {
	p := ppFree.Get().(*pp)
	p.panicking = false
	p.erroring = false
	p.wrapErrs = false
	p.fmt.init(&p.buf)
	return p
}

// free saves used pp structs in ppFree; avoids an allocation per invocation.
func (p *pp) free() {
	// Proper usage of a sync.Pool requires each entry to have approximately
	// the same memory cost. To obtain this property when the stored type
	// contains a variably-sized buffer, we add a hard limit on the maximum buffer
	// to place back in the pool.
	//
	// See https://golang.org/issue/23199
	if cap(p.buf) > 64<<10 {
		return
	}

	p.buf = p.buf[:0]
	p.arg = nil
	p.value = reflect.Value{}
	p.wrappedErr = nil
	ppFree.Put(p)
}

func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }

func (p *pp) Precision() (prec int, ok bool) { return p.fmt.prec, p.fmt.precPresent }

func (p *pp) Flag(b int) bool {
	switch b {
	case '-':
		return p.fmt.minus
	case '+':
		return p.fmt.plus || p.fmt.plusV
	case '#':
		return p.fmt.sharp || p.fmt.sharpV
	case ' ':
		return p.fmt.space
	case '0':
		return p.fmt.zero
	}
	return false
}

// Implement Write so we can call Fprintf on a pp (through State), for
// recursive use in custom verbs.
func (p *pp) Write(b []byte) (ret int, err error) {
	p.buf.write(b)
	return len(b), nil
}

// Implement WriteString so that we can call io.WriteString
// on a pp (through state), for efficiency.
func (p *pp) WriteString(s string) (ret int, err error) {
	p.buf.writeString(s)
	return len(s), nil
}

// These routines end in 'f' and take a format string.

// Fprintf formats according to a format specifier and writes to w.
// It returns the number of bytes written and any write error encountered.
func Fprintf(w io.Writer, format string, a ...any) (n int, err error) {
	p := newPrinter()
	p.doPrintf(format, a)
	n, err = w.Write(p.buf)
	p.free()
	return
}

//// Printf formats according to a format specifier and writes to standard output.
//// It returns the number of bytes written and any write error encountered.
//func Printf(format string, a ...any) (n int, err error) {
//	return Fprintf(os.Stdout, format, a...)
//}

// Sprintf formats according to a format specifier and returns the resulting string.
func Sprintf(format string, a ...any) string {
	p := newPrinter()
	p.doPrintf(format, a)
	s := string(p.buf)
	p.free()
	return s
}

// These routines do not take a format string

// Fprint formats using the default formats for its operands and writes to w.
// Spaces are added between operands when neither is a string.
// It returns the number of bytes written and any write error encountered.
func Fprint(w io.Writer, a ...any) (n int, err error) {
	p := newPrinter()
	p.doPrint(a)
	n, err = w.Write(p.buf)
	p.free()
	return
}

//// Print formats using the default formats for its operands and writes to standard output.
//// Spaces are added between operands when neither is a string.
//// It returns the number of bytes written and any write error encountered.
//func Print(a ...any) (n int, err error) {
//	return Fprint(os.Stdout, a...)
//}

// Sprint formats using the default formats for its operands and returns the resulting string.
// Spaces are added between operands when neither is a string.
func Sprint(a ...any) string {
	p := newPrinter()
	p.doPrint(a)
	s := string(p.buf)
	p.free()
	return s
}

// These routines end in 'ln', do not take a format string,
// always add spaces between operands, and add a newline
// after the last operand.

// Fprintln formats using the default formats for its operands and writes to w.
// Spaces are always added between operands and a newline is appended.
// It returns the number of bytes written and any write error encountered.
func Fprintln(w io.Writer, a ...any) (n int, err error) {
	p := newPrinter()
	p.doPrintln(a)
	n, err = w.Write(p.buf)
	p.free()
	return
}

//// Println formats using the default formats for its operands and writes to standard output.
//// Spaces are always added between operands and a newline is appended.
//// It returns the number of bytes written and any write error encountered.
//func Println(a ...any) (n int, err error) {
//	return Fprintln(os.Stdout, a...)
//}

// Sprintln formats using the default formats for its operands and returns the resulting string.
// Spaces are always added between operands and a newline is appended.
func Sprintln(a ...any) string {
	p := newPrinter()
	p.doPrintln(a)
	s := string(p.buf)
	p.free()
	return s
}

// getField gets the i'th field of the struct value.
// If the field is itself is an interface, return a value for
// the thing inside the interface, not the interface itself.
func getField(v reflect.Value, i int) reflect.Value {
	val := v.Field(i)
	if val.Kind() == reflect.Interface && !val.IsNil() {
		val = val.Elem()
	}
	return val
}

// tooLarge reports whether the magnitude of the integer is
// too large to be used as a formatting width or precision.
func tooLarge(x int) bool {
	const max int = 1e6
	return x > max || x < -max
}

// parsenum converts ASCII to integer.  num is 0 (and isnum is false) if no number present.
func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
	if start >= end {
		return 0, false, end
	}
	for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
		if tooLarge(num) {
			return 0, false, end // Overflow; crazy long number most likely.
		}
		num = num*10 + int(s[newi]-'0')
		isnum = true
	}
	return
}

func (p *pp) unknownType(v reflect.Value) {
	if !v.IsValid() {
		p.buf.writeString(nilAngleString)
		return
	}
	p.buf.writeByte('?')
	p.buf.writeString(v.Type().String())
	p.buf.writeByte('?')
}

func (p *pp) badVerb(verb rune) {
	p.erroring = true
	p.buf.writeString(percentBangString)
	p.buf.writeRune(verb)
	p.buf.writeByte('(')
	switch {
	case p.arg != nil:
		p.buf.writeString(reflect.TypeOf(p.arg).String())
		p.buf.writeByte('=')
		p.printArg(p.arg, 'v')
	case p.value.IsValid():
		p.buf.writeString(p.value.Type().String())
		p.buf.writeByte('=')
		p.printValue(p.value, 'v', 0)
	default:
		p.buf.writeString(nilAngleString)
	}
	p.buf.writeByte(')')
	p.erroring = false
}

func (p *pp) fmtBool(v bool, verb rune) {
	switch verb {
	case 't', 'v':
		p.fmt.fmtBoolean(v)
	default:
		p.badVerb(verb)
	}
}

// fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
// not, as requested, by temporarily setting the sharp flag.
func (p *pp) fmt0x64(v uint64, leading0x bool) {
	sharp := p.fmt.sharp
	p.fmt.sharp = leading0x
	p.fmt.fmtInteger(v, 16, unsigned, 'v', ldigits)
	p.fmt.sharp = sharp
}

// fmtInteger formats a signed or unsigned integer.
func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
	switch verb {
	case 'v':
		if p.fmt.sharpV && !isSigned {
			p.fmt0x64(v, true)
		} else {
			p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
		}
	case 'd':
		p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
	case 'b':
		p.fmt.fmtInteger(v, 2, isSigned, verb, ldigits)
	case 'o', 'O':
		p.fmt.fmtInteger(v, 8, isSigned, verb, ldigits)
	case 'x':
		p.fmt.fmtInteger(v, 16, isSigned, verb, ldigits)
	case 'X':
		p.fmt.fmtInteger(v, 16, isSigned, verb, udigits)
	case 'c':
		p.fmt.fmtC(v)
	case 'q':
		p.fmt.fmtQc(v)
	case 'U':
		p.fmt.fmtUnicode(v)
	default:
		p.badVerb(verb)
	}
}

// fmtFloat formats a float. The default precision for each verb
// is specified as last argument in the call to fmt_float.
func (p *pp) fmtFloat(v float64, size int, verb rune) {
	switch verb {
	case 'v':
		p.fmt.fmtFloat(v, size, 'g', -1)
	case 'b', 'g', 'G', 'x', 'X':
		p.fmt.fmtFloat(v, size, verb, -1)
	case 'f', 'e', 'E':
		p.fmt.fmtFloat(v, size, verb, 6)
	case 'F':
		p.fmt.fmtFloat(v, size, 'f', 6)
	default:
		p.badVerb(verb)
	}
}

// fmtComplex formats a complex number v with
// r = real(v) and j = imag(v) as (r+ji) using
// fmtFloat for r and j formatting.
func (p *pp) fmtComplex(v complex128, size int, verb rune) {
	// Make sure any unsupported verbs are found before the
	// calls to fmtFloat to not generate an incorrect error string.
	switch verb {
	case 'v', 'b', 'g', 'G', 'x', 'X', 'f', 'F', 'e', 'E':
		oldPlus := p.fmt.plus
		p.buf.writeByte('(')
		p.fmtFloat(real(v), size/2, verb)
		// Imaginary part always has a sign.
		p.fmt.plus = true
		p.fmtFloat(imag(v), size/2, verb)
		p.buf.writeString("i)")
		p.fmt.plus = oldPlus
	default:
		p.badVerb(verb)
	}
}

func (p *pp) fmtString(v string, verb rune) {
	switch verb {
	case 'v':
		if p.fmt.sharpV {
			p.fmt.fmtQ(v)
		} else {
			p.fmt.fmtS(v)
		}
	case 's':
		p.fmt.fmtS(v)
	case 'x':
		p.fmt.fmtSx(v, ldigits)
	case 'X':
		p.fmt.fmtSx(v, udigits)
	case 'q':
		p.fmt.fmtQ(v)
	default:
		p.badVerb(verb)
	}
}

func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
	switch verb {
	case 'v', 'd':
		if p.fmt.sharpV {
			p.buf.writeString(typeString)
			if v == nil {
				p.buf.writeString(nilParenString)
				return
			}
			p.buf.writeByte('{')
			for i, c := range v {
				if i > 0 {
					p.buf.writeString(commaSpaceString)
				}
				p.fmt0x64(uint64(c), true)
			}
			p.buf.writeByte('}')
		} else {
			p.buf.writeByte('[')
			for i, c := range v {
				if i > 0 {
					p.buf.writeByte(' ')
				}
				p.fmt.fmtInteger(uint64(c), 10, unsigned, verb, ldigits)
			}
			p.buf.writeByte(']')
		}
	case 's':
		p.fmt.fmtBs(v)
	case 'x':
		p.fmt.fmtBx(v, ldigits)
	case 'X':
		p.fmt.fmtBx(v, udigits)
	case 'q':
		p.fmt.fmtQ(string(v))
	default:
		p.printValue(reflect.ValueOf(v), verb, 0)
	}
}

func (p *pp) fmtPointer(value reflect.Value, verb rune) {
	var u uintptr
	switch value.Kind() {
	case reflect.Chan, reflect.Func, reflect.Map, reflect.Pointer, reflect.Slice, reflect.UnsafePointer:
		u = value.Pointer()
	default:
		p.badVerb(verb)
		return
	}

	switch verb {
	case 'v':
		if p.fmt.sharpV {
			p.buf.writeByte('(')
			p.buf.writeString(value.Type().String())
			p.buf.writeString(")(")
			if u == 0 {
				p.buf.writeString(nilString)
			} else {
				p.fmt0x64(uint64(u), true)
			}
			p.buf.writeByte(')')
		} else {
			if u == 0 {
				p.fmt.padString(nilAngleString)
			} else {
				p.fmt0x64(uint64(u), !p.fmt.sharp)
			}
		}
	case 'p':
		p.fmt0x64(uint64(u), !p.fmt.sharp)
	case 'b', 'o', 'd', 'x', 'X':
		p.fmtInteger(uint64(u), unsigned, verb)
	default:
		p.badVerb(verb)
	}
}

func (p *pp) catchPanic(arg any, verb rune, method string) {
	if err := recover(); err != nil {
		// If it's a nil pointer, just say "<nil>". The likeliest causes are a
		// Stringer that fails to guard against nil or a nil pointer for a
		// value receiver, and in either case, "<nil>" is a nice result.
		if v := reflect.ValueOf(arg); v.Kind() == reflect.Pointer && v.IsNil() {
			p.buf.writeString(nilAngleString)
			return
		}
		// Otherwise print a concise panic message. Most of the time the panic
		// value will print itself nicely.
		if p.panicking {
			// Nested panics; the recursion in printArg cannot succeed.
			panic(err)
		}

		oldFlags := p.fmt.fmtFlags
		// For this output we want default behavior.
		p.fmt.clearflags()

		p.buf.writeString(percentBangString)
		p.buf.writeRune(verb)
		p.buf.writeString(panicString)
		p.buf.writeString(method)
		p.buf.writeString(" method: ")
		p.panicking = true
		p.printArg(err, 'v')
		p.panicking = false
		p.buf.writeByte(')')

		p.fmt.fmtFlags = oldFlags
	}
}

func (p *pp) handleMethods(verb rune) (handled bool) {
	if p.erroring {
		return
	}
	if verb == 'w' {
		// It is invalid to use %w other than with Errorf, more than once,
		// or with a non-error arg.
		err, ok := p.arg.(error)
		if !ok || !p.wrapErrs || p.wrappedErr != nil {
			p.wrappedErr = nil
			p.wrapErrs = false
			p.badVerb(verb)
			return true
		}
		p.wrappedErr = err
		// If the arg is a Formatter, pass 'v' as the verb to it.
		verb = 'v'
	}

	// Is it a Formatter?
	if formatter, ok := p.arg.(Formatter); ok {
		handled = true
		defer p.catchPanic(p.arg, verb, "Format")
		formatter.Format(p, verb)
		return
	}

	// If we're doing Go syntax and the argument knows how to supply it, take care of it now.
	if p.fmt.sharpV {
		if stringer, ok := p.arg.(GoStringer); ok {
			handled = true
			defer p.catchPanic(p.arg, verb, "GoString")
			// Print the result of GoString unadorned.
			p.fmt.fmtS(stringer.GoString())
			return
		}
	} else {
		// If a string is acceptable according to the format, see if
		// the value satisfies one of the string-valued interfaces.
		// Println etc. set verb to %v, which is "stringable".
		switch verb {
		case 'v', 's', 'x', 'X', 'q':
			// Is it an error or Stringer?
			// The duplication in the bodies is necessary:
			// setting handled and deferring catchPanic
			// must happen before calling the method.
			switch v := p.arg.(type) {
			case error:
				handled = true
				defer p.catchPanic(p.arg, verb, "Error")
				p.fmtString(v.Error(), verb)
				return

			case Stringer:
				handled = true
				defer p.catchPanic(p.arg, verb, "String")
				p.fmtString(v.String(), verb)
				return
			}
		}
	}
	return false
}

func (p *pp) printArg(arg any, verb rune) {
	p.arg = arg
	p.value = reflect.Value{}

	if arg == nil {
		switch verb {
		case 'T', 'v':
			p.fmt.padString(nilAngleString)
		default:
			p.badVerb(verb)
		}
		return
	}

	// Special processing considerations.
	// %T (the value's type) and %p (its address) are special; we always do them first.
	switch verb {
	case 'T':
		p.fmt.fmtS(reflect.TypeOf(arg).String())
		return
	case 'p':
		p.fmtPointer(reflect.ValueOf(arg), 'p')
		return
	}

	// Some types can be done without reflection.
	switch f := arg.(type) {
	case bool:
		p.fmtBool(f, verb)
	case float32:
		p.fmtFloat(float64(f), 32, verb)
	case float64:
		p.fmtFloat(f, 64, verb)
	case complex64:
		p.fmtComplex(complex128(f), 64, verb)
	case complex128:
		p.fmtComplex(f, 128, verb)
	case int:
		p.fmtInteger(uint64(f), signed, verb)
	case int8:
		p.fmtInteger(uint64(f), signed, verb)
	case int16:
		p.fmtInteger(uint64(f), signed, verb)
	case int32:
		p.fmtInteger(uint64(f), signed, verb)
	case int64:
		p.fmtInteger(uint64(f), signed, verb)
	case uint:
		p.fmtInteger(uint64(f), unsigned, verb)
	case uint8:
		p.fmtInteger(uint64(f), unsigned, verb)
	case uint16:
		p.fmtInteger(uint64(f), unsigned, verb)
	case uint32:
		p.fmtInteger(uint64(f), unsigned, verb)
	case uint64:
		p.fmtInteger(f, unsigned, verb)
	case uintptr:
		p.fmtInteger(uint64(f), unsigned, verb)
	case string:
		p.fmtString(f, verb)
	case []byte:
		p.fmtBytes(f, verb, "[]byte")
	case reflect.Value:
		// Handle extractable values with special methods
		// since printValue does not handle them at depth 0.
		if f.IsValid() && f.CanInterface() {
			p.arg = f.Interface()
			if p.handleMethods(verb) {
				return
			}
		}
		p.printValue(f, verb, 0)
	default:
		// If the type is not simple, it might have methods.
		if !p.handleMethods(verb) {
			// Need to use reflection, since the type had no
			// interface methods that could be used for formatting.
			p.printValue(reflect.ValueOf(f), verb, 0)
		}
	}
}

// printValue is similar to printArg but starts with a reflect value, not an interface{} value.
// It does not handle 'p' and 'T' verbs because these should have been already handled by printArg.
func (p *pp) printValue(value reflect.Value, verb rune, depth int) {
	// Handle values with special methods if not already handled by printArg (depth == 0).
	if depth > 0 && value.IsValid() && value.CanInterface() {
		p.arg = value.Interface()
		if p.handleMethods(verb) {
			return
		}
	}
	p.arg = nil
	p.value = value

	switch f := value; value.Kind() {
	case reflect.Invalid:
		if depth == 0 {
			p.buf.writeString(invReflectString)
		} else {
			switch verb {
			case 'v':
				p.buf.writeString(nilAngleString)
			default:
				p.badVerb(verb)
			}
		}
	case reflect.Bool:
		p.fmtBool(f.Bool(), verb)
	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
		p.fmtInteger(uint64(f.Int()), signed, verb)
	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
		p.fmtInteger(f.Uint(), unsigned, verb)
	case reflect.Float32:
		p.fmtFloat(f.Float(), 32, verb)
	case reflect.Float64:
		p.fmtFloat(f.Float(), 64, verb)
	case reflect.Complex64:
		p.fmtComplex(f.Complex(), 64, verb)
	case reflect.Complex128:
		p.fmtComplex(f.Complex(), 128, verb)
	case reflect.String:
		p.fmtString(f.String(), verb)
	case reflect.Map:
		if p.fmt.sharpV {
			p.buf.writeString(f.Type().String())
			if f.IsNil() {
				p.buf.writeString(nilParenString)
				return
			}
			p.buf.writeByte('{')
		} else {
			p.buf.writeString(mapString)
		}
		sorted := fmtsort.Sort(f)
		for i, key := range sorted.Key {
			if i > 0 {
				if p.fmt.sharpV {
					p.buf.writeString(commaSpaceString)
				} else {
					p.buf.writeByte(' ')
				}
			}
			p.printValue(key, verb, depth+1)
			p.buf.writeByte(':')
			p.printValue(sorted.Value[i], verb, depth+1)
		}
		if p.fmt.sharpV {
			p.buf.writeByte('}')
		} else {
			p.buf.writeByte(']')
		}
	case reflect.Struct:
		if p.fmt.sharpV {
			p.buf.writeString(f.Type().String())
		}
		p.buf.writeByte('{')
		for i := 0; i < f.NumField(); i++ {
			if i > 0 {
				if p.fmt.sharpV {
					p.buf.writeString(commaSpaceString)
				} else {
					p.buf.writeByte(' ')
				}
			}
			if p.fmt.plusV || p.fmt.sharpV {
				if name := f.Type().Field(i).Name; name != "" {
					p.buf.writeString(name)
					p.buf.writeByte(':')
				}
			}
			p.printValue(getField(f, i), verb, depth+1)
		}
		p.buf.writeByte('}')
	case reflect.Interface:
		value := f.Elem()
		if !value.IsValid() {
			if p.fmt.sharpV {
				p.buf.writeString(f.Type().String())
				p.buf.writeString(nilParenString)
			} else {
				p.buf.writeString(nilAngleString)
			}
		} else {
			p.printValue(value, verb, depth+1)
		}
	case reflect.Array, reflect.Slice:
		switch verb {
		case 's', 'q', 'x', 'X':
			// Handle byte and uint8 slices and arrays special for the above verbs.
			t := f.Type()
			if t.Elem().Kind() == reflect.Uint8 {
				var bytes []byte
				if f.Kind() == reflect.Slice {
					bytes = f.Bytes()
				} else if f.CanAddr() {
					bytes = f.Slice(0, f.Len()).Bytes()
				} else {
					// We have an array, but we cannot Slice() a non-addressable array,
					// so we build a slice by hand. This is a rare case but it would be nice
					// if reflection could help a little more.
					bytes = make([]byte, f.Len())
					for i := range bytes {
						bytes[i] = byte(f.Index(i).Uint())
					}
				}
				p.fmtBytes(bytes, verb, t.String())
				return
			}
		}
		if p.fmt.sharpV {
			p.buf.writeString(f.Type().String())
			if f.Kind() == reflect.Slice && f.IsNil() {
				p.buf.writeString(nilParenString)
				return
			}
			p.buf.writeByte('{')
			for i := 0; i < f.Len(); i++ {
				if i > 0 {
					p.buf.writeString(commaSpaceString)
				}
				p.printValue(f.Index(i), verb, depth+1)
			}
			p.buf.writeByte('}')
		} else {
			p.buf.writeByte('[')
			for i := 0; i < f.Len(); i++ {
				if i > 0 {
					p.buf.writeByte(' ')
				}
				p.printValue(f.Index(i), verb, depth+1)
			}
			p.buf.writeByte(']')
		}
	case reflect.Pointer:
		// pointer to array or slice or struct? ok at top level
		// but not embedded (avoid loops)
		if depth == 0 && f.Pointer() != 0 {
			switch a := f.Elem(); a.Kind() {
			case reflect.Array, reflect.Slice, reflect.Struct, reflect.Map:
				p.buf.writeByte('&')
				p.printValue(a, verb, depth+1)
				return
			}
		}
		fallthrough
	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
		p.fmtPointer(f, verb)
	default:
		p.unknownType(f)
	}
}

// intFromArg gets the argNumth element of a. On return, isInt reports whether the argument has integer type.
func intFromArg(a []any, argNum int) (num int, isInt bool, newArgNum int) {
	newArgNum = argNum
	if argNum < len(a) {
		num, isInt = a[argNum].(int) // Almost always OK.
		if !isInt {
			// Work harder.
			switch v := reflect.ValueOf(a[argNum]); v.Kind() {
			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
				n := v.Int()
				if int64(int(n)) == n {
					num = int(n)
					isInt = true
				}
			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
				n := v.Uint()
				if int64(n) >= 0 && uint64(int(n)) == n {
					num = int(n)
					isInt = true
				}
			default:
				// Already 0, false.
			}
		}
		newArgNum = argNum + 1
		if tooLarge(num) {
			num = 0
			isInt = false
		}
	}
	return
}

// parseArgNumber returns the value of the bracketed number, minus 1
// (explicit argument numbers are one-indexed but we want zero-indexed).
// The opening bracket is known to be present at format[0].
// The returned values are the index, the number of bytes to consume
// up to the closing paren, if present, and whether the number parsed
// ok. The bytes to consume will be 1 if no closing paren is present.
func parseArgNumber(format string) (index int, wid int, ok bool) {
	// There must be at least 3 bytes: [n].
	if len(format) < 3 {
		return 0, 1, false
	}

	// Find closing bracket.
	for i := 1; i < len(format); i++ {
		if format[i] == ']' {
			width, ok, newi := parsenum(format, 1, i)
			if !ok || newi != i {
				return 0, i + 1, false
			}
			return width - 1, i + 1, true // arg numbers are one-indexed and skip paren.
		}
	}
	return 0, 1, false
}

// argNumber returns the next argument to evaluate, which is either the value of the passed-in
// argNum or the value of the bracketed integer that begins format[i:]. It also returns
// the new value of i, that is, the index of the next byte of the format to process.
func (p *pp) argNumber(argNum int, format string, i int, numArgs int) (newArgNum, newi int, found bool) {
	if len(format) <= i || format[i] != '[' {
		return argNum, i, false
	}
	p.reordered = true
	index, wid, ok := parseArgNumber(format[i:])
	if ok && 0 <= index && index < numArgs {
		return index, i + wid, true
	}
	p.goodArgNum = false
	return argNum, i + wid, ok
}

func (p *pp) badArgNum(verb rune) {
	p.buf.writeString(percentBangString)
	p.buf.writeRune(verb)
	p.buf.writeString(badIndexString)
}

func (p *pp) missingArg(verb rune) {
	p.buf.writeString(percentBangString)
	p.buf.writeRune(verb)
	p.buf.writeString(missingString)
}

func (p *pp) doPrintf(format string, a []any) {
	end := len(format)
	argNum := 0         // we process one argument per non-trivial format
	afterIndex := false // previous item in format was an index like [3].
	p.reordered = false
formatLoop:
	for i := 0; i < end; {
		p.goodArgNum = true
		lasti := i
		for i < end && format[i] != '%' {
			i++
		}
		if i > lasti {
			p.buf.writeString(format[lasti:i])
		}
		if i >= end {
			// done processing format string
			break
		}

		// Process one verb
		i++

		// Do we have flags?
		p.fmt.clearflags()
	simpleFormat:
		for ; i < end; i++ {
			c := format[i]
			switch c {
			case '#':
				p.fmt.sharp = true
			case '0':
				p.fmt.zero = !p.fmt.minus // Only allow zero padding to the left.
			case '+':
				p.fmt.plus = true
			case '-':
				p.fmt.minus = true
				p.fmt.zero = false // Do not pad with zeros to the right.
			case ' ':
				p.fmt.space = true
			default:
				// Fast path for common case of ascii lower case simple verbs
				// without precision or width or argument indices.
				if 'a' <= c && c <= 'z' && argNum < len(a) {
					if c == 'v' {
						// Go syntax
						p.fmt.sharpV = p.fmt.sharp
						p.fmt.sharp = false
						// Struct-field syntax
						p.fmt.plusV = p.fmt.plus
						p.fmt.plus = false
					}
					p.printArg(a[argNum], rune(c))
					argNum++
					i++
					continue formatLoop
				}
				// Format is more complex than simple flags and a verb or is malformed.
				break simpleFormat
			}
		}

		// Do we have an explicit argument index?
		argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))

		// Do we have width?
		if i < end && format[i] == '*' {
			i++
			p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)

			if !p.fmt.widPresent {
				p.buf.writeString(badWidthString)
			}

			// We have a negative width, so take its value and ensure
			// that the minus flag is set
			if p.fmt.wid < 0 {
				p.fmt.wid = -p.fmt.wid
				p.fmt.minus = true
				p.fmt.zero = false // Do not pad with zeros to the right.
			}
			afterIndex = false
		} else {
			p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
			if afterIndex && p.fmt.widPresent { // "%[3]2d"
				p.goodArgNum = false
			}
		}

		// Do we have precision?
		if i+1 < end && format[i] == '.' {
			i++
			if afterIndex { // "%[3].2d"
				p.goodArgNum = false
			}
			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
			if i < end && format[i] == '*' {
				i++
				p.fmt.prec, p.fmt.precPresent, argNum = intFromArg(a, argNum)
				// Negative precision arguments don't make sense
				if p.fmt.prec < 0 {
					p.fmt.prec = 0
					p.fmt.precPresent = false
				}
				if !p.fmt.precPresent {
					p.buf.writeString(badPrecString)
				}
				afterIndex = false
			} else {
				p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i, end)
				if !p.fmt.precPresent {
					p.fmt.prec = 0
					p.fmt.precPresent = true
				}
			}
		}

		if !afterIndex {
			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
		}

		if i >= end {
			p.buf.writeString(noVerbString)
			break
		}

		verb, size := rune(format[i]), 1
		if verb >= utf8.RuneSelf {
			verb, size = utf8.DecodeRuneInString(format[i:])
		}
		i += size

		switch {
		case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
			p.buf.writeByte('%')
		case !p.goodArgNum:
			p.badArgNum(verb)
		case argNum >= len(a): // No argument left over to print for the current verb.
			p.missingArg(verb)
		case verb == 'v':
			// Go syntax
			p.fmt.sharpV = p.fmt.sharp
			p.fmt.sharp = false
			// Struct-field syntax
			p.fmt.plusV = p.fmt.plus
			p.fmt.plus = false
			fallthrough
		default:
			p.printArg(a[argNum], verb)
			argNum++
		}
	}

	// Check for extra arguments unless the call accessed the arguments
	// out of order, in which case it's too expensive to detect if they've all
	// been used and arguably OK if they're not.
	if !p.reordered && argNum < len(a) {
		p.fmt.clearflags()
		p.buf.writeString(extraString)
		for i, arg := range a[argNum:] {
			if i > 0 {
				p.buf.writeString(commaSpaceString)
			}
			if arg == nil {
				p.buf.writeString(nilAngleString)
			} else {
				p.buf.writeString(reflect.TypeOf(arg).String())
				p.buf.writeByte('=')
				p.printArg(arg, 'v')
			}
		}
		p.buf.writeByte(')')
	}
}

func (p *pp) doPrint(a []any) {
	prevString := false
	for argNum, arg := range a {
		isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
		// Add a space between two non-string arguments.
		if argNum > 0 && !isString && !prevString {
			p.buf.writeByte(' ')
		}
		p.printArg(arg, 'v')
		prevString = isString
	}
}

// doPrintln is like doPrint but always adds a space between arguments
// and a newline after the last argument.
func (p *pp) doPrintln(a []any) {
	for argNum, arg := range a {
		if argNum > 0 {
			p.buf.writeByte(' ')
		}
		p.printArg(arg, 'v')
	}
	p.buf.writeByte('\n')
}

scan.go

// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package fmt

import (
	"errors"
	"io"
	"math"
	"reflect"
	"strconv"
	"sync"
	"unicode/utf8"
)

// ScanState represents the scanner state passed to custom scanners.
// Scanners may do rune-at-a-time scanning or ask the ScanState
// to discover the next space-delimited token.
type ScanState interface {
	// ReadRune reads the next rune (Unicode code point) from the input.
	// If invoked during Scanln, Fscanln, or Sscanln, ReadRune() will
	// return EOF after returning the first '\n' or when reading beyond
	// the specified width.
	ReadRune() (r rune, size int, err error)
	// UnreadRune causes the next call to ReadRune to return the same rune.
	UnreadRune() error
	// SkipSpace skips space in the input. Newlines are treated appropriately
	// for the operation being performed; see the package documentation
	// for more information.
	SkipSpace()
	// Token skips space in the input if skipSpace is true, then returns the
	// run of Unicode code points c satisfying f(c).  If f is nil,
	// !unicode.IsSpace(c) is used; that is, the token will hold non-space
	// characters. Newlines are treated appropriately for the operation being
	// performed; see the package documentation for more information.
	// The returned slice points to shared data that may be overwritten
	// by the next call to Token, a call to a Scan function using the ScanState
	// as input, or when the calling Scan method returns.
	Token(skipSpace bool, f func(rune) bool) (token []byte, err error)
	// Width returns the value of the width option and whether it has been set.
	// The unit is Unicode code points.
	Width() (wid int, ok bool)
	// Because ReadRune is implemented by the interface, Read should never be
	// called by the scanning routines and a valid implementation of
	// ScanState may choose always to return an error from Read.
	Read(buf []byte) (n int, err error)
}

// Scanner is implemented by any value that has a Scan method, which scans
// the input for the representation of a value and stores the result in the
// receiver, which must be a pointer to be useful. The Scan method is called
// for any argument to Scan, Scanf, or Scanln that implements it.
type Scanner interface {
	Scan(state ScanState, verb rune) error
}

//// Scan scans text read from standard input, storing successive
//// space-separated values into successive arguments. Newlines count
//// as space. It returns the number of items successfully scanned.
//// If that is less than the number of arguments, err will report why.
//func Scan(a ...any) (n int, err error) {
//	return Fscan(os.Stdin, a...)
//}

//// Scanln is similar to Scan, but stops scanning at a newline and
//// after the final item there must be a newline or EOF.
//func Scanln(a ...any) (n int, err error) {
//	return Fscanln(os.Stdin, a...)
//}

//// Scanf scans text read from standard input, storing successive
//// space-separated values into successive arguments as determined by
//// the format. It returns the number of items successfully scanned.
//// If that is less than the number of arguments, err will report why.
//// Newlines in the input must match newlines in the format.
//// The one exception: the verb %c always scans the next rune in the
//// input, even if it is a space (or tab etc.) or newline.
//func Scanf(format string, a ...any) (n int, err error) {
//	return Fscanf(os.Stdin, format, a...)
//}

type stringReader string

func (r *stringReader) Read(b []byte) (n int, err error) {
	n = copy(b, *r)
	*r = (*r)[n:]
	if n == 0 {
		err = io.EOF
	}
	return
}

// Sscan scans the argument string, storing successive space-separated
// values into successive arguments. Newlines count as space. It
// returns the number of items successfully scanned. If that is less
// than the number of arguments, err will report why.
func Sscan(str string, a ...any) (n int, err error) {
	return Fscan((*stringReader)(&str), a...)
}

// Sscanln is similar to Sscan, but stops scanning at a newline and
// after the final item there must be a newline or EOF.
func Sscanln(str string, a ...any) (n int, err error) {
	return Fscanln((*stringReader)(&str), a...)
}

// Sscanf scans the argument string, storing successive space-separated
// values into successive arguments as determined by the format. It
// returns the number of items successfully parsed.
// Newlines in the input must match newlines in the format.
func Sscanf(str string, format string, a ...any) (n int, err error) {
	return Fscanf((*stringReader)(&str), format, a...)
}

// Fscan scans text read from r, storing successive space-separated
// values into successive arguments. Newlines count as space. It
// returns the number of items successfully scanned. If that is less
// than the number of arguments, err will report why.
func Fscan(r io.Reader, a ...any) (n int, err error) {
	s, old := newScanState(r, true, false)
	n, err = s.doScan(a)
	s.free(old)
	return
}

// Fscanln is similar to Fscan, but stops scanning at a newline and
// after the final item there must be a newline or EOF.
func Fscanln(r io.Reader, a ...any) (n int, err error) {
	s, old := newScanState(r, false, true)
	n, err = s.doScan(a)
	s.free(old)
	return
}

// Fscanf scans text read from r, storing successive space-separated
// values into successive arguments as determined by the format. It
// returns the number of items successfully parsed.
// Newlines in the input must match newlines in the format.
func Fscanf(r io.Reader, format string, a ...any) (n int, err error) {
	s, old := newScanState(r, false, false)
	n, err = s.doScanf(format, a)
	s.free(old)
	return
}

// scanError represents an error generated by the scanning software.
// It's used as a unique signature to identify such errors when recovering.
type scanError struct {
	err error
}

const eof = -1

// ss is the internal implementation of ScanState.
type ss struct {
	rs    io.RuneScanner // where to read input
	buf   buffer         // token accumulator
	count int            // runes consumed so far.
	atEOF bool           // already read EOF
	ssave
}

// ssave holds the parts of ss that need to be
// saved and restored on recursive scans.
type ssave struct {
	validSave bool // is or was a part of an actual ss.
	nlIsEnd   bool // whether newline terminates scan
	nlIsSpace bool // whether newline counts as white space
	argLimit  int  // max value of ss.count for this arg; argLimit <= limit
	limit     int  // max value of ss.count.
	maxWid    int  // width of this arg.
}

// The Read method is only in ScanState so that ScanState
// satisfies io.Reader. It will never be called when used as
// intended, so there is no need to make it actually work.
func (s *ss) Read(buf []byte) (n int, err error) {
	return 0, errors.New("ScanState's Read should not be called. Use ReadRune")
}

func (s *ss) ReadRune() (r rune, size int, err error) {
	if s.atEOF || s.count >= s.argLimit {
		err = io.EOF
		return
	}

	r, size, err = s.rs.ReadRune()
	if err == nil {
		s.count++
		if s.nlIsEnd && r == '\n' {
			s.atEOF = true
		}
	} else if err == io.EOF {
		s.atEOF = true
	}
	return
}

func (s *ss) Width() (wid int, ok bool) {
	if s.maxWid == hugeWid {
		return 0, false
	}
	return s.maxWid, true
}

// The public method returns an error; this private one panics.
// If getRune reaches EOF, the return value is EOF (-1).
func (s *ss) getRune() (r rune) {
	r, _, err := s.ReadRune()
	if err != nil {
		if err == io.EOF {
			return eof
		}
		s.error(err)
	}
	return
}

// mustReadRune turns io.EOF into a panic(io.ErrUnexpectedEOF).
// It is called in cases such as string scanning where an EOF is a
// syntax error.
func (s *ss) mustReadRune() (r rune) {
	r = s.getRune()
	if r == eof {
		s.error(io.ErrUnexpectedEOF)
	}
	return
}

func (s *ss) UnreadRune() error {
	s.rs.UnreadRune()
	s.atEOF = false
	s.count--
	return nil
}

func (s *ss) error(err error) {
	panic(scanError{err})
}

func (s *ss) errorString(err string) {
	panic(scanError{errors.New(err)})
}

func (s *ss) Token(skipSpace bool, f func(rune) bool) (tok []byte, err error) {
	defer func() {
		if e := recover(); e != nil {
			if se, ok := e.(scanError); ok {
				err = se.err
			} else {
				panic(e)
			}
		}
	}()
	if f == nil {
		f = notSpace
	}
	s.buf = s.buf[:0]
	tok = s.token(skipSpace, f)
	return
}

// space is a copy of the unicode.White_Space ranges,
// to avoid depending on package unicode.
var space = [][2]uint16{
	{0x0009, 0x000d},
	{0x0020, 0x0020},
	{0x0085, 0x0085},
	{0x00a0, 0x00a0},
	{0x1680, 0x1680},
	{0x2000, 0x200a},
	{0x2028, 0x2029},
	{0x202f, 0x202f},
	{0x205f, 0x205f},
	{0x3000, 0x3000},
}

func isSpace(r rune) bool {
	if r >= 1<<16 {
		return false
	}
	rx := uint16(r)
	for _, rng := range space {
		if rx < rng[0] {
			return false
		}
		if rx <= rng[1] {
			return true
		}
	}
	return false
}

// notSpace is the default scanning function used in Token.
func notSpace(r rune) bool {
	return !isSpace(r)
}

// readRune is a structure to enable reading UTF-8 encoded code points
// from an io.Reader. It is used if the Reader given to the scanner does
// not already implement io.RuneScanner.
type readRune struct {
	reader   io.Reader
	buf      [utf8.UTFMax]byte // used only inside ReadRune
	pending  int               // number of bytes in pendBuf; only >0 for bad UTF-8
	pendBuf  [utf8.UTFMax]byte // bytes left over
	peekRune rune              // if >=0 next rune; when <0 is ^(previous Rune)
}

// readByte returns the next byte from the input, which may be
// left over from a previous read if the UTF-8 was ill-formed.
func (r *readRune) readByte() (b byte, err error) {
	if r.pending > 0 {
		b = r.pendBuf[0]
		copy(r.pendBuf[0:], r.pendBuf[1:])
		r.pending--
		return
	}
	n, err := io.ReadFull(r.reader, r.pendBuf[:1])
	if n != 1 {
		return 0, err
	}
	return r.pendBuf[0], err
}

// ReadRune returns the next UTF-8 encoded code point from the
// io.Reader inside r.
func (r *readRune) ReadRune() (rr rune, size int, err error) {
	if r.peekRune >= 0 {
		rr = r.peekRune
		r.peekRune = ^r.peekRune
		size = utf8.RuneLen(rr)
		return
	}
	r.buf[0], err = r.readByte()
	if err != nil {
		return
	}
	if r.buf[0] < utf8.RuneSelf { // fast check for common ASCII case
		rr = rune(r.buf[0])
		size = 1 // Known to be 1.
		// Flip the bits of the rune so it's available to UnreadRune.
		r.peekRune = ^rr
		return
	}
	var n int
	for n = 1; !utf8.FullRune(r.buf[:n]); n++ {
		r.buf[n], err = r.readByte()
		if err != nil {
			if err == io.EOF {
				err = nil
				break
			}
			return
		}
	}
	rr, size = utf8.DecodeRune(r.buf[:n])
	if size < n { // an error, save the bytes for the next read
		copy(r.pendBuf[r.pending:], r.buf[size:n])
		r.pending += n - size
	}
	// Flip the bits of the rune so it's available to UnreadRune.
	r.peekRune = ^rr
	return
}

func (r *readRune) UnreadRune() error {
	if r.peekRune >= 0 {
		return errors.New("fmt: scanning called UnreadRune with no rune available")
	}
	// Reverse bit flip of previously read rune to obtain valid >=0 state.
	r.peekRune = ^r.peekRune
	return nil
}

var ssFree = sync.Pool{
	New: func() any { return new(ss) },
}

// newScanState allocates a new ss struct or grab a cached one.
func newScanState(r io.Reader, nlIsSpace, nlIsEnd bool) (s *ss, old ssave) {
	s = ssFree.Get().(*ss)
	if rs, ok := r.(io.RuneScanner); ok {
		s.rs = rs
	} else {
		s.rs = &readRune{reader: r, peekRune: -1}
	}
	s.nlIsSpace = nlIsSpace
	s.nlIsEnd = nlIsEnd
	s.atEOF = false
	s.limit = hugeWid
	s.argLimit = hugeWid
	s.maxWid = hugeWid
	s.validSave = true
	s.count = 0
	return
}

// free saves used ss structs in ssFree; avoid an allocation per invocation.
func (s *ss) free(old ssave) {
	// If it was used recursively, just restore the old state.
	if old.validSave {
		s.ssave = old
		return
	}
	// Don't hold on to ss structs with large buffers.
	if cap(s.buf) > 1024 {
		return
	}
	s.buf = s.buf[:0]
	s.rs = nil
	ssFree.Put(s)
}

// SkipSpace provides Scan methods the ability to skip space and newline
// characters in keeping with the current scanning mode set by format strings
// and Scan/Scanln.
func (s *ss) SkipSpace() {
	for {
		r := s.getRune()
		if r == eof {
			return
		}
		if r == '\r' && s.peek("\n") {
			continue
		}
		if r == '\n' {
			if s.nlIsSpace {
				continue
			}
			s.errorString("unexpected newline")
			return
		}
		if !isSpace(r) {
			s.UnreadRune()
			break
		}
	}
}

// token returns the next space-delimited string from the input. It
// skips white space. For Scanln, it stops at newlines. For Scan,
// newlines are treated as spaces.
func (s *ss) token(skipSpace bool, f func(rune) bool) []byte {
	if skipSpace {
		s.SkipSpace()
	}
	// read until white space or newline
	for {
		r := s.getRune()
		if r == eof {
			break
		}
		if !f(r) {
			s.UnreadRune()
			break
		}
		s.buf.writeRune(r)
	}
	return s.buf
}

var complexError = errors.New("syntax error scanning complex number")
var boolError = errors.New("syntax error scanning boolean")

func indexRune(s string, r rune) int {
	for i, c := range s {
		if c == r {
			return i
		}
	}
	return -1
}

// consume reads the next rune in the input and reports whether it is in the ok string.
// If accept is true, it puts the character into the input token.
func (s *ss) consume(ok string, accept bool) bool {
	r := s.getRune()
	if r == eof {
		return false
	}
	if indexRune(ok, r) >= 0 {
		if accept {
			s.buf.writeRune(r)
		}
		return true
	}
	if r != eof && accept {
		s.UnreadRune()
	}
	return false
}

// peek reports whether the next character is in the ok string, without consuming it.
func (s *ss) peek(ok string) bool {
	r := s.getRune()
	if r != eof {
		s.UnreadRune()
	}
	return indexRune(ok, r) >= 0
}

func (s *ss) notEOF() {
	// Guarantee there is data to be read.
	if r := s.getRune(); r == eof {
		panic(io.EOF)
	}
	s.UnreadRune()
}

// accept checks the next rune in the input. If it's a byte (sic) in the string, it puts it in the
// buffer and returns true. Otherwise it return false.
func (s *ss) accept(ok string) bool {
	return s.consume(ok, true)
}

// okVerb verifies that the verb is present in the list, setting s.err appropriately if not.
func (s *ss) okVerb(verb rune, okVerbs, typ string) bool {
	for _, v := range okVerbs {
		if v == verb {
			return true
		}
	}
	s.errorString("bad verb '%" + string(verb) + "' for " + typ)
	return false
}

// scanBool returns the value of the boolean represented by the next token.
func (s *ss) scanBool(verb rune) bool {
	s.SkipSpace()
	s.notEOF()
	if !s.okVerb(verb, "tv", "boolean") {
		return false
	}
	// Syntax-checking a boolean is annoying. We're not fastidious about case.
	switch s.getRune() {
	case '0':
		return false
	case '1':
		return true
	case 't', 'T':
		if s.accept("rR") && (!s.accept("uU") || !s.accept("eE")) {
			s.error(boolError)
		}
		return true
	case 'f', 'F':
		if s.accept("aA") && (!s.accept("lL") || !s.accept("sS") || !s.accept("eE")) {
			s.error(boolError)
		}
		return false
	}
	return false
}

// Numerical elements
const (
	binaryDigits      = "01"
	octalDigits       = "01234567"
	decimalDigits     = "0123456789"
	hexadecimalDigits = "0123456789aAbBcCdDeEfF"
	sign              = "+-"
	period            = "."
	exponent          = "eEpP"
)

// getBase returns the numeric base represented by the verb and its digit string.
func (s *ss) getBase(verb rune) (base int, digits string) {
	s.okVerb(verb, "bdoUxXv", "integer") // sets s.err
	base = 10
	digits = decimalDigits
	switch verb {
	case 'b':
		base = 2
		digits = binaryDigits
	case 'o':
		base = 8
		digits = octalDigits
	case 'x', 'X', 'U':
		base = 16
		digits = hexadecimalDigits
	}
	return
}

// scanNumber returns the numerical string with specified digits starting here.
func (s *ss) scanNumber(digits string, haveDigits bool) string {
	if !haveDigits {
		s.notEOF()
		if !s.accept(digits) {
			s.errorString("expected integer")
		}
	}
	for s.accept(digits) {
	}
	return string(s.buf)
}

// scanRune returns the next rune value in the input.
func (s *ss) scanRune(bitSize int) int64 {
	s.notEOF()
	r := s.getRune()
	n := uint(bitSize)
	x := (int64(r) << (64 - n)) >> (64 - n)
	if x != int64(r) {
		s.errorString("overflow on character value " + string(r))
	}
	return int64(r)
}

// scanBasePrefix reports whether the integer begins with a base prefix
// and returns the base, digit string, and whether a zero was found.
// It is called only if the verb is %v.
func (s *ss) scanBasePrefix() (base int, digits string, zeroFound bool) {
	if !s.peek("0") {
		return 0, decimalDigits + "_", false
	}
	s.accept("0")
	// Special cases for 0, 0b, 0o, 0x.
	switch {
	case s.peek("bB"):
		s.consume("bB", true)
		return 0, binaryDigits + "_", true
	case s.peek("oO"):
		s.consume("oO", true)
		return 0, octalDigits + "_", true
	case s.peek("xX"):
		s.consume("xX", true)
		return 0, hexadecimalDigits + "_", true
	default:
		return 0, octalDigits + "_", true
	}
}

// scanInt returns the value of the integer represented by the next
// token, checking for overflow. Any error is stored in s.err.
func (s *ss) scanInt(verb rune, bitSize int) int64 {
	if verb == 'c' {
		return s.scanRune(bitSize)
	}
	s.SkipSpace()
	s.notEOF()
	base, digits := s.getBase(verb)
	haveDigits := false
	if verb == 'U' {
		if !s.consume("U", false) || !s.consume("+", false) {
			s.errorString("bad unicode format ")
		}
	} else {
		s.accept(sign) // If there's a sign, it will be left in the token buffer.
		if verb == 'v' {
			base, digits, haveDigits = s.scanBasePrefix()
		}
	}
	tok := s.scanNumber(digits, haveDigits)
	i, err := strconv.ParseInt(tok, base, 64)
	if err != nil {
		s.error(err)
	}
	n := uint(bitSize)
	x := (i << (64 - n)) >> (64 - n)
	if x != i {
		s.errorString("integer overflow on token " + tok)
	}
	return i
}

// scanUint returns the value of the unsigned integer represented
// by the next token, checking for overflow. Any error is stored in s.err.
func (s *ss) scanUint(verb rune, bitSize int) uint64 {
	if verb == 'c' {
		return uint64(s.scanRune(bitSize))
	}
	s.SkipSpace()
	s.notEOF()
	base, digits := s.getBase(verb)
	haveDigits := false
	if verb == 'U' {
		if !s.consume("U", false) || !s.consume("+", false) {
			s.errorString("bad unicode format ")
		}
	} else if verb == 'v' {
		base, digits, haveDigits = s.scanBasePrefix()
	}
	tok := s.scanNumber(digits, haveDigits)
	i, err := strconv.ParseUint(tok, base, 64)
	if err != nil {
		s.error(err)
	}
	n := uint(bitSize)
	x := (i << (64 - n)) >> (64 - n)
	if x != i {
		s.errorString("unsigned integer overflow on token " + tok)
	}
	return i
}

// floatToken returns the floating-point number starting here, no longer than swid
// if the width is specified. It's not rigorous about syntax because it doesn't check that
// we have at least some digits, but Atof will do that.
func (s *ss) floatToken() string {
	s.buf = s.buf[:0]
	// NaN?
	if s.accept("nN") && s.accept("aA") && s.accept("nN") {
		return string(s.buf)
	}
	// leading sign?
	s.accept(sign)
	// Inf?
	if s.accept("iI") && s.accept("nN") && s.accept("fF") {
		return string(s.buf)
	}
	digits := decimalDigits + "_"
	exp := exponent
	if s.accept("0") && s.accept("xX") {
		digits = hexadecimalDigits + "_"
		exp = "pP"
	}
	// digits?
	for s.accept(digits) {
	}
	// decimal point?
	if s.accept(period) {
		// fraction?
		for s.accept(digits) {
		}
	}
	// exponent?
	if s.accept(exp) {
		// leading sign?
		s.accept(sign)
		// digits?
		for s.accept(decimalDigits + "_") {
		}
	}
	return string(s.buf)
}

// complexTokens returns the real and imaginary parts of the complex number starting here.
// The number might be parenthesized and has the format (N+Ni) where N is a floating-point
// number and there are no spaces within.
func (s *ss) complexTokens() (real, imag string) {
	// TODO: accept N and Ni independently?
	parens := s.accept("(")
	real = s.floatToken()
	s.buf = s.buf[:0]
	// Must now have a sign.
	if !s.accept("+-") {
		s.error(complexError)
	}
	// Sign is now in buffer
	imagSign := string(s.buf)
	imag = s.floatToken()
	if !s.accept("i") {
		s.error(complexError)
	}
	if parens && !s.accept(")") {
		s.error(complexError)
	}
	return real, imagSign + imag
}

func hasX(s string) bool {
	for i := 0; i < len(s); i++ {
		if s[i] == 'x' || s[i] == 'X' {
			return true
		}
	}
	return false
}

// convertFloat converts the string to a float64value.
func (s *ss) convertFloat(str string, n int) float64 {
	// strconv.ParseFloat will handle "+0x1.fp+2",
	// but we have to implement our non-standard
	// decimal+binary exponent mix (1.2p4) ourselves.
	if p := indexRune(str, 'p'); p >= 0 && !hasX(str) {
		// Atof doesn't handle power-of-2 exponents,
		// but they're easy to evaluate.
		f, err := strconv.ParseFloat(str[:p], n)
		if err != nil {
			// Put full string into error.
			if e, ok := err.(*strconv.NumError); ok {
				e.Num = str
			}
			s.error(err)
		}
		m, err := strconv.Atoi(str[p+1:])
		if err != nil {
			// Put full string into error.
			if e, ok := err.(*strconv.NumError); ok {
				e.Num = str
			}
			s.error(err)
		}
		return math.Ldexp(f, m)
	}
	f, err := strconv.ParseFloat(str, n)
	if err != nil {
		s.error(err)
	}
	return f
}

// convertComplex converts the next token to a complex128 value.
// The atof argument is a type-specific reader for the underlying type.
// If we're reading complex64, atof will parse float32s and convert them
// to float64's to avoid reproducing this code for each complex type.
func (s *ss) scanComplex(verb rune, n int) complex128 {
	if !s.okVerb(verb, floatVerbs, "complex") {
		return 0
	}
	s.SkipSpace()
	s.notEOF()
	sreal, simag := s.complexTokens()
	real := s.convertFloat(sreal, n/2)
	imag := s.convertFloat(simag, n/2)
	return complex(real, imag)
}

// convertString returns the string represented by the next input characters.
// The format of the input is determined by the verb.
func (s *ss) convertString(verb rune) (str string) {
	if !s.okVerb(verb, "svqxX", "string") {
		return ""
	}
	s.SkipSpace()
	s.notEOF()
	switch verb {
	case 'q':
		str = s.quotedString()
	case 'x', 'X':
		str = s.hexString()
	default:
		str = string(s.token(true, notSpace)) // %s and %v just return the next word
	}
	return
}

// quotedString returns the double- or back-quoted string represented by the next input characters.
func (s *ss) quotedString() string {
	s.notEOF()
	quote := s.getRune()
	switch quote {
	case '`':
		// Back-quoted: Anything goes until EOF or back quote.
		for {
			r := s.mustReadRune()
			if r == quote {
				break
			}
			s.buf.writeRune(r)
		}
		return string(s.buf)
	case '"':
		// Double-quoted: Include the quotes and let strconv.Unquote do the backslash escapes.
		s.buf.writeByte('"')
		for {
			r := s.mustReadRune()
			s.buf.writeRune(r)
			if r == '\\' {
				// In a legal backslash escape, no matter how long, only the character
				// immediately after the escape can itself be a backslash or quote.
				// Thus we only need to protect the first character after the backslash.
				s.buf.writeRune(s.mustReadRune())
			} else if r == '"' {
				break
			}
		}
		result, err := strconv.Unquote(string(s.buf))
		if err != nil {
			s.error(err)
		}
		return result
	default:
		s.errorString("expected quoted string")
	}
	return ""
}

// hexDigit returns the value of the hexadecimal digit.
func hexDigit(d rune) (int, bool) {
	digit := int(d)
	switch digit {
	case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
		return digit - '0', true
	case 'a', 'b', 'c', 'd', 'e', 'f':
		return 10 + digit - 'a', true
	case 'A', 'B', 'C', 'D', 'E', 'F':
		return 10 + digit - 'A', true
	}
	return -1, false
}

// hexByte returns the next hex-encoded (two-character) byte from the input.
// It returns ok==false if the next bytes in the input do not encode a hex byte.
// If the first byte is hex and the second is not, processing stops.
func (s *ss) hexByte() (b byte, ok bool) {
	rune1 := s.getRune()
	if rune1 == eof {
		return
	}
	value1, ok := hexDigit(rune1)
	if !ok {
		s.UnreadRune()
		return
	}
	value2, ok := hexDigit(s.mustReadRune())
	if !ok {
		s.errorString("illegal hex digit")
		return
	}
	return byte(value1<<4 | value2), true
}

// hexString returns the space-delimited hexpair-encoded string.
func (s *ss) hexString() string {
	s.notEOF()
	for {
		b, ok := s.hexByte()
		if !ok {
			break
		}
		s.buf.writeByte(b)
	}
	if len(s.buf) == 0 {
		s.errorString("no hex data for %x string")
		return ""
	}
	return string(s.buf)
}

const (
	floatVerbs = "beEfFgGv"

	hugeWid = 1 << 30

	intBits     = 32 << (^uint(0) >> 63)
	uintptrBits = 32 << (^uintptr(0) >> 63)
)

// scanPercent scans a literal percent character.
func (s *ss) scanPercent() {
	s.SkipSpace()
	s.notEOF()
	if !s.accept("%") {
		s.errorString("missing literal %")
	}
}

// scanOne scans a single value, deriving the scanner from the type of the argument.
func (s *ss) scanOne(verb rune, arg any) {
	s.buf = s.buf[:0]
	var err error
	// If the parameter has its own Scan method, use that.
	if v, ok := arg.(Scanner); ok {
		err = v.Scan(s, verb)
		if err != nil {
			if err == io.EOF {
				err = io.ErrUnexpectedEOF
			}
			s.error(err)
		}
		return
	}

	switch v := arg.(type) {
	case *bool:
		*v = s.scanBool(verb)
	case *complex64:
		*v = complex64(s.scanComplex(verb, 64))
	case *complex128:
		*v = s.scanComplex(verb, 128)
	case *int:
		*v = int(s.scanInt(verb, intBits))
	case *int8:
		*v = int8(s.scanInt(verb, 8))
	case *int16:
		*v = int16(s.scanInt(verb, 16))
	case *int32:
		*v = int32(s.scanInt(verb, 32))
	case *int64:
		*v = s.scanInt(verb, 64)
	case *uint:
		*v = uint(s.scanUint(verb, intBits))
	case *uint8:
		*v = uint8(s.scanUint(verb, 8))
	case *uint16:
		*v = uint16(s.scanUint(verb, 16))
	case *uint32:
		*v = uint32(s.scanUint(verb, 32))
	case *uint64:
		*v = s.scanUint(verb, 64)
	case *uintptr:
		*v = uintptr(s.scanUint(verb, uintptrBits))
	// Floats are tricky because you want to scan in the precision of the result, not
	// scan in high precision and convert, in order to preserve the correct error condition.
	case *float32:
		if s.okVerb(verb, floatVerbs, "float32") {
			s.SkipSpace()
			s.notEOF()
			*v = float32(s.convertFloat(s.floatToken(), 32))
		}
	case *float64:
		if s.okVerb(verb, floatVerbs, "float64") {
			s.SkipSpace()
			s.notEOF()
			*v = s.convertFloat(s.floatToken(), 64)
		}
	case *string:
		*v = s.convertString(verb)
	case *[]byte:
		// We scan to string and convert so we get a copy of the data.
		// If we scanned to bytes, the slice would point at the buffer.
		*v = []byte(s.convertString(verb))
	default:
		val := reflect.ValueOf(v)
		ptr := val
		if ptr.Kind() != reflect.Pointer {
			s.errorString("type not a pointer: " + val.Type().String())
			return
		}
		switch v := ptr.Elem(); v.Kind() {
		case reflect.Bool:
			v.SetBool(s.scanBool(verb))
		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
			v.SetInt(s.scanInt(verb, v.Type().Bits()))
		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
			v.SetUint(s.scanUint(verb, v.Type().Bits()))
		case reflect.String:
			v.SetString(s.convertString(verb))
		case reflect.Slice:
			// For now, can only handle (renamed) []byte.
			typ := v.Type()
			if typ.Elem().Kind() != reflect.Uint8 {
				s.errorString("can't scan type: " + val.Type().String())
			}
			str := s.convertString(verb)
			v.Set(reflect.MakeSlice(typ, len(str), len(str)))
			for i := 0; i < len(str); i++ {
				v.Index(i).SetUint(uint64(str[i]))
			}
		case reflect.Float32, reflect.Float64:
			s.SkipSpace()
			s.notEOF()
			v.SetFloat(s.convertFloat(s.floatToken(), v.Type().Bits()))
		case reflect.Complex64, reflect.Complex128:
			v.SetComplex(s.scanComplex(verb, v.Type().Bits()))
		default:
			s.errorString("can't scan type: " + val.Type().String())
		}
	}
}

// errorHandler turns local panics into error returns.
func errorHandler(errp *error) {
	if e := recover(); e != nil {
		if se, ok := e.(scanError); ok { // catch local error
			*errp = se.err
		} else if eof, ok := e.(error); ok && eof == io.EOF { // out of input
			*errp = eof
		} else {
			panic(e)
		}
	}
}

// doScan does the real work for scanning without a format string.
func (s *ss) doScan(a []any) (numProcessed int, err error) {
	defer errorHandler(&err)
	for _, arg := range a {
		s.scanOne('v', arg)
		numProcessed++
	}
	// Check for newline (or EOF) if required (Scanln etc.).
	if s.nlIsEnd {
		for {
			r := s.getRune()
			if r == '\n' || r == eof {
				break
			}
			if !isSpace(r) {
				s.errorString("expected newline")
				break
			}
		}
	}
	return
}

// advance determines whether the next characters in the input match
// those of the format. It returns the number of bytes (sic) consumed
// in the format. All runs of space characters in either input or
// format behave as a single space. Newlines are special, though:
// newlines in the format must match those in the input and vice versa.
// This routine also handles the %% case. If the return value is zero,
// either format starts with a % (with no following %) or the input
// is empty. If it is negative, the input did not match the string.
func (s *ss) advance(format string) (i int) {
	for i < len(format) {
		fmtc, w := utf8.DecodeRuneInString(format[i:])

		// Space processing.
		// In the rest of this comment "space" means spaces other than newline.
		// Newline in the format matches input of zero or more spaces and then newline or end-of-input.
		// Spaces in the format before the newline are collapsed into the newline.
		// Spaces in the format after the newline match zero or more spaces after the corresponding input newline.
		// Other spaces in the format match input of one or more spaces or end-of-input.
		if isSpace(fmtc) {
			newlines := 0
			trailingSpace := false
			for isSpace(fmtc) && i < len(format) {
				if fmtc == '\n' {
					newlines++
					trailingSpace = false
				} else {
					trailingSpace = true
				}
				i += w
				fmtc, w = utf8.DecodeRuneInString(format[i:])
			}
			for j := 0; j < newlines; j++ {
				inputc := s.getRune()
				for isSpace(inputc) && inputc != '\n' {
					inputc = s.getRune()
				}
				if inputc != '\n' && inputc != eof {
					s.errorString("newline in format does not match input")
				}
			}
			if trailingSpace {
				inputc := s.getRune()
				if newlines == 0 {
					// If the trailing space stood alone (did not follow a newline),
					// it must find at least one space to consume.
					if !isSpace(inputc) && inputc != eof {
						s.errorString("expected space in input to match format")
					}
					if inputc == '\n' {
						s.errorString("newline in input does not match format")
					}
				}
				for isSpace(inputc) && inputc != '\n' {
					inputc = s.getRune()
				}
				if inputc != eof {
					s.UnreadRune()
				}
			}
			continue
		}

		// Verbs.
		if fmtc == '%' {
			// % at end of string is an error.
			if i+w == len(format) {
				s.errorString("missing verb: % at end of format string")
			}
			// %% acts like a real percent
			nextc, _ := utf8.DecodeRuneInString(format[i+w:]) // will not match % if string is empty
			if nextc != '%' {
				return
			}
			i += w // skip the first %
		}

		// Literals.
		inputc := s.mustReadRune()
		if fmtc != inputc {
			s.UnreadRune()
			return -1
		}
		i += w
	}
	return
}

// doScanf does the real work when scanning with a format string.
// At the moment, it handles only pointers to basic types.
func (s *ss) doScanf(format string, a []any) (numProcessed int, err error) {
	defer errorHandler(&err)
	end := len(format) - 1
	// We process one item per non-trivial format
	for i := 0; i <= end; {
		w := s.advance(format[i:])
		if w > 0 {
			i += w
			continue
		}
		// Either we failed to advance, we have a percent character, or we ran out of input.
		if format[i] != '%' {
			// Can't advance format. Why not?
			if w < 0 {
				s.errorString("input does not match format")
			}
			// Otherwise at EOF; "too many operands" error handled below
			break
		}
		i++ // % is one byte

		// do we have 20 (width)?
		var widPresent bool
		s.maxWid, widPresent, i = parsenum(format, i, end)
		if !widPresent {
			s.maxWid = hugeWid
		}

		c, w := utf8.DecodeRuneInString(format[i:])
		i += w

		if c != 'c' {
			s.SkipSpace()
		}
		if c == '%' {
			s.scanPercent()
			continue // Do not consume an argument.
		}
		s.argLimit = s.limit
		if f := s.count + s.maxWid; f < s.argLimit {
			s.argLimit = f
		}

		if numProcessed >= len(a) { // out of operands
			s.errorString("too few operands for format '%" + format[i-w:] + "'")
			break
		}
		arg := a[numProcessed]

		s.scanOne(c, arg)
		numProcessed++
		s.argLimit = s.limit
	}
	if numProcessed < len(a) {
		s.errorString("too many operands")
	}
	return
}

This file is a modified version of the Go1.18.1 fmt package.
You can place them anywhere you like and import them.

It can be used with semihosting.
https://github.com/tinygo-org/drivers/blob/release/examples/semihosting/semihosting.go

package machine

import (
        "machine/fmt"
	"tinygo.org/x/drivers/semihosting"
)

func foo() {
        semihosting.Stdout.Write([]byte(fmt.Sprintf("hello %s\n", "tinygo")))
}