Day 2 of AoC in aa64

aoc2021_day2.cc

#include <iostream>

__attribute__ ((naked)) void asm_main() {
    __asm__ volatile (R"(
        // x19: Pointer to file
        // x20: xpos
        // x21: depth
        // x22: aim

        part1:
            stp x19, x30, [sp, -16]! // save return address and x19, lower stack
            stp x20, x21, [sp, -16]! // Back up x20 and x21 for use too
            stp x22, x23, [sp, -16]! // Same for x22 and x23
            sub sp, sp, 32 // Reserve some stack space for whatever use
            sub sp, sp, 4096 // Reserve 4096 bytes for strings

            mov x20, 0 // Init depth and xpos to 0
            mov x21, 0

            adr x0, filename
            adr x1, file_perms
            bl fopen // x0 = file pointer
            mov x19, x0

        loop:
            bl feof // Check for eof as a sanity check
            cbnz x0, end

            mov x0, x19
            adr x1, input_fmt // Read entry
            add x2, sp, 4096
            add x3, x2, 32
            bl fscanf

            add x0, sp, 4096 // Check if string is "up"
            adr x1, up_str
            bl string_cmp
            cbz w0, is_up

            add x0, sp, 4096 // Check if string is "down"
            adr x1, down_str
            bl string_cmp
            cbz w0, is_down

            // if it's none of those then it's forward
            ldr w0, [sp, 4096 + 32]
            add w20, w20, w0 // add to xpos
            mov x0, x19 // x0 = file
            b loop

        end:
            // print result
            adr x0, result1_fmt
            mul w1, w20, w21 // result = xpos * depth
            mov w2, w20
            mov w3, w21
            bl printf
        
        part2:
            // Reset depth, xpos and aim
            mov w20, 0
            mov w21, 0
            mov w22, 0
            // Rewind filestream
            mov x0, x19
            bl rewind
            mov x0, x19

        loop2:
            bl feof // Check for eof as a sanity check
            cbnz x0, end2

            mov x0, x19
            adr x1, input_fmt // Read entry
            add x2, sp, 4096
            add x3, x2, 32
            bl fscanf

            add x0, sp, 4096 // Check if string is "up"
            adr x1, up_str
            bl string_cmp
            cbz w0, is_up2

            add x0, sp, 4096 // Check if string is "down"
            adr x1, down_str
            bl string_cmp
            cbz w0, is_down2

            // if it's none of those then it's forward
            ldr w0, [sp, 4096 + 32]
            add w20, w20, w0 // add to xpos
            mul w0, w0, w22 // w0 = aim * number
            add w21, w21, w0 // add to depth
            mov x0, x19 // x0 = file
            b loop2

        end2:
            // print result
            adr x0, result2_fmt
            mul w1, w20, w21 // result = xpos * depth
            mov w2, w20
            mov w3, w21
            mov w4, w22
            bl printf

        // undo the mess we made
        cleanup:
            add sp, sp, 4096
            add sp, sp, 32
            ldp x22, x23, [sp], 16
            ldp x20, x21, [sp], 16
            ldp x19, x30, [sp], 16
            ret

        is_up:
            ldr w0, [sp, 4096 + 32]
            sub w21, w21, w0 // sub from depth
            mov x0, x19 // x0 = file
            b loop
        is_down:
            ldr w0, [sp, 4096 + 32]
            add w21, w21, w0 // add to depth
            mov x0, x19 // x0 = file
            b loop
        is_up2:
            ldr w0, [sp, 4096 + 32]
            sub w22, w22, w0 // sub from aim
            mov x0, x19 // x0 = file
            b loop2
        is_down2:
            ldr w0, [sp, 4096 + 32]
            add w22, w22, w0 // add to aim
            mov x0, x19 // x0 = file
            b loop2

        // bool string_cmp (const char* a, const char* b)
        // w0 = 0 if equal, w0 = 1 if not equal
        string_cmp:
            ldrb w2, [x0], 1 // Read char from string 1
            ldrb w3, [x1], 1 // Read char from string 2
            cmp w2, w3 // If the characters are not equal then the strings are not equal
            b.ne not_equal
            cbz w2, equal // If they're equal and one of them is the null terminator, the strings are equal
            b string_cmp

        not_equal:
            mov w0, 1
            ret
        equal:
            mov w0, 0
            ret

        filename:
            .asciz "input.in"
        file_perms:
            .asciz "r"
        input_fmt:
            .asciz "%s %d\n"
        result1_fmt:
            .asciz "Result of part 1: %d\nXpos: %d  Depth: %d\n"
        result2_fmt:
            .asciz "Result of part 2: %d\nXpos: %d  Depth: %d\nAim: %d\n"
        down_str:
            .asciz "down"
        up_str:
            .asciz "up"
    )");
}


int main() {
    asm_main();
}