2023 adventofcode.com (arm64 assembler)

one.s

// https://adventofcode.com/2023/day/1


// as -o one.o one.s && ld -o one one.o
// echo -e "1abc2\npqr3stu8vwx\na1b2c3d4e5f\ntreb7uchet\n" | ./one


.equ __NR_read, 63
.equ __NR_write, 64
.equ __NR_exit_group, 94


.text
.global _start
_start:
		mov x6, #0 // total

next_line:	bl get_line
		cbz x0, done

		bl scan_line

		// n = 10*first + last
		mov x10, #10
		madd x4, x10, x4, x5

		// total += n
		add x6, x6, x4

		b next_line

done:		mov x0, x6
		bl print_int

		mov x8, #__NR_exit_group
		svc 0


.global scan_line
scan_line:
		adrp x0, buf
		add x0, x0, :lo12:buf
		mov x1, #0
		mov x4, #-1 // first digit
		mov x5, #-1 // last digit
scan_next:	ldrb w2, [x0, x1]
		cbz x2, scan_done
		add x1, x1, #1
		// digit?
		sub x3, x2, #'0'
		cmp x3, 9
		bhi scan_next
		// do we have a first digit yet?
		cmp x4, #0
		csel x4, x3, x4, lt
		// whatever we just saw is by definition last [so far]
		mov x5, x3
		b scan_next
		# TODO: what if there were no digits?
scan_done:	ret


.global get_line
get_line:
		adrp x1, buf
		add x1, x1, :lo12:buf
		mov x3, #0
get_char:	mov x0, #0
		mov x2, #1
		mov x8, #__NR_read
		svc 0
		cmp x0, #0
		ble read_failed
		ldrb w2, [x1]
		add x1, x1, #1
		add x3, x3, #1
		cmp x3, #80
		bge read_failed
		cmp x2, #'\n'
		bne get_char 
		cmp x3, #1
		ble read_failed
		sub x1, x1, #1
		strb wzr, [x1]
		mov x0, #1
		ret
read_failed:	mov x0, #0
		ret


.global print_int
print_int:
		adrp x1, buf
		add x1, x1, :lo12:buf
		add x1, x1, #32
		mov x3, x1

		mov x10, #10

		mov x2, #'\n'
		sub x1, x1, #1
		strb w2, [x1]
print_loop:	cbz x0, print_done
		// x9 = x0/10, x2 = x0%10
		mov x8, #10
		sdiv x9, x0, x8
		msub x2, x9, x8, x0
		add x2, x2, #'0'
		mov x0, x9

		sub x1, x1, #1
		strb w2, [x1]
		b print_loop
print_done:	mov x0, #1
		sub x2, x3, x1
		mov x8, #__NR_write
		svc 0
		ret


.bss
.global buf
buf:
		.zero 80