janky_float_printer.c

#include <stdio.h>
#include <stdint.h>
#include <math.h>

#define nl() printf("\n")
#define fl_mark() printf("s/exp    /mantissa\n");
#define is_finite(_fl) ((_fl & 0x7F800000) != 0x7F800000)
#define is_normalized(_fl) is_finite(~(_fl))

void
print_u32(void *obj)
{
    if (!obj) return;
    uint32_t buf = *(uint32_t *)obj;
    for (uint32_t ct = 1 << 31; ct; ct >>= 1) {
        printf(buf & ct ? "1" : "0");
    }
}

// exp is locked between -23 and 23
// handle more special cases
// truncating and rounding

void
print_float(float fl)
{
    const uint32_t buf = *(uint32_t *)&fl;
    int is_pos = !(buf & 1 << 31);

    if (!is_normalized(buf)) {
        if (buf & 0x007FFFFF) {
            printf("denormalized");
            return;
        }
    }

    if (!is_finite(buf)) {
        printf("%s%s"
            , is_pos ? "" : "-"
            , buf & 0x007FFFFF ? "nan" : "inf");
        return;
    }

    int exp = (uint8_t)(buf >> 23) - 127;
    uint32_t mantissa = buf & 0x007FFFFF | 0x00800000;
    uint32_t int_part = mantissa >> (23 - exp);
    if (exp < 0) {
        mantissa >>= -exp;
        int_part = exp = 0;
    }

    uint64_t mult = 1000000000000000000 >> 1;
    uint64_t dec_part = 0;
    for (uint32_t ct = 1 << (22 - exp); ct; ct >>= 1) {
        if (mantissa & ct) {
            dec_part += mult;
            // radix or whatev
            // inc max decimal places
        }
        mult >>= 1;
    }

    // round and truncate

    printf("%s%u.%018lu", is_pos ? "" : "-", int_part, dec_part);
}

int
main(void)
{
    print_float(INFINITY); nl();
    print_float(NAN); nl();
    print_float(-INFINITY); nl();
    print_float(-NAN); nl();
    nl();
    print_float(0.); nl();
    print_float(*(float *)&(uint32_t) { 0x00400000 }); nl();
    nl();
    print_float(1.); nl();
    print_float(2.); nl();
    print_float(-2.); nl();
    print_float(45.); nl();
    print_float(-45.5); nl();
    print_float(30.125); nl();
    print_float(30.03042145987018); nl();
    nl();
    print_float(0.5); nl();
    print_float(0.12345); nl();
    print_float(0.012345); nl();
    print_float(0.000045); nl();
    nl();

    return 0;
}