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olavfosse/.S

Created January 2, 2025 13:54
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  1. olavfosse created this gist Jan 2, 2025.
    122 changes: 122 additions & 0 deletions .S
    View file
    Original file line number Diff line number Diff line change
    @@ -0,0 +1,122 @@
    .intel_syntax noprefix
    .global _start
    # - [x] exit with 1337
    #- [ ] print 1-100

    .section .data
    int_fmt: .string "%d\n"
    .section .text
    _start:
    mov rcx, 100
    iteration:
    # start = 4, end = 4 (end is not excluseive)
    mov r14, 4 # start
    mov r15, 4 # end
    # if divisble by 3, start = 0
    mov rdi, 101
    sub rdi, rcx
    mov r13, 3
    call divisible_by
    jne not_divisible_by_3
    mov r14, 0
    not_divisible_by_3:
    # if divisble by 5, end = 7
    mov r13, 5
    call divisible_by
    jne not_divisible_by_5
    mov r15, 8
    not_divisible_by_5:
    # if start == end, print_int, otherwise print [start..end]
    cmp r14, r15
    jne divisible_by_3_or_5
    call print_int
    mov rdi, rcx
    jmp not_divisible_by_3_or_5
    divisible_by_3_or_5:
    call print_from_start_to_end
    call print_newline
    not_divisible_by_3_or_5:
    loop iteration
    mov rax, 60
    mov rdi, 3
    syscall

    print_int:
    mov r10, 10
    mov rax, rdi
    mov rdx, 0
    div r10
    add rdx, 48
    mov byte [buffer+2], dl
    # least significant digit written ^^^
    mov rdx, 0
    div r10
    add rdx, 48
    mov byte [buffer+1], dl
    # second least significant digit wirtten ^^^
    mov rdx, 0
    div r10
    add rdx, 48
    mov byte [buffer], dl
    call print_int_buf
    call print_newline
    ret

    print_int_buf:
    mov rax, 1
    # rdi: the digit count
    mov r11, rdi # count of how many more digits i need to print
    # the buf contains the digits in reverse
    lea rsi, [rip+buffer+1]
    mov rbx, rcx
    mov rdi, 1
    mov rdx, 3
    syscall
    mov rcx, rbx
    ret

    print_digit:
    add rdi, 48
    mov [buffer+2], rdi
    call print_int_buf
    ret

    print_newline:
    mov rax, 1
    mov rdi, 1
    lea rsi, [rip+buffer+3]
    mov BYTE PTR [rsi], 10
    mov rbx, rcx
    mov rdx, 1
    syscall
    mov rcx, rbx
    ret

    divisible_by:
    # is rdi divisible by r13
    xor rdx, rdx
    mov rax, rdi
    div r13
    cmp rdx, 0
    ret

    print_from_start_to_end:
    # prints from r14 to r15, will change r14 and r15
    mov rax, 1
    mov rdi, 1
    lea rsi, [rip+strings]
    add rsi, r14
    mov rdx, r15
    sub rdx, r14
    mov rbx, rcx
    syscall
    mov rcx, rbx
    ret

    .section .bss
    buffer:
    .skip 4
    .section .data
    strings:
    .ascii "fizz"
    .ascii "buzz"