NASM BF Interpreter

%include "io64.inc"

section .bss
    input:      resb 20000
    array:      resb 20000
    loop_stack: resq 100

section .text
    global main
    extern _read

main:
    mov rbp, rsp

    sub rsp, 40
    mov rcx, 0
    lea rdx, [input]
    mov r8, 20000
    call _read
    mov byte [input + rax], 0
    add rsp, 40

    lea rsi, [input]
    lea rdi, [array]
    lea rbp, [loop_stack]

    mov r8, 0
    mov r9, 0
    mov r10, 0

.scan:
    mov al, [rsi]

    test al, al
    jz .done
    inc rsi

    test r10, r10
    jz .normal
    cmp al, '['
    je .skip_up
    cmp al, ']'
    je .skip_down
    jmp .scan
.skip_up:
    inc r10
    jmp .scan
.skip_down:
    dec r10
    jmp .scan

.normal:
    call loop_start_sub
    test cl, cl
    jne .scan

    call loop_end_sub
    test cl, cl
    jne .scan

    call plus_sub
    test cl, cl
    jne .scan

    call minus_sub
    test cl, cl
    jne .scan

    call right_sub
    test cl, cl
    jne .scan

    call left_sub
    test cl, cl
    jne .scan

    call dot_sub

    jmp .scan

.done:
    ret


plus_sub:
    cmp al, '+'
    sete cl
    jne .ret
    inc byte [rdi + r8]
.ret:
    ret


minus_sub:
    cmp al, '-'
    sete cl
    jne .ret
    dec byte [rdi + r8]
.ret:
    ret


right_sub:
    cmp al, '>'
    sete cl
    jne .ret
    inc r8
.ret:
    ret


left_sub:
    cmp al, '<'
    sete cl
    jne .ret
    dec r8
.ret:
    ret


dot_sub:
    cmp al, '.'
    jne .ret
    movzx rax, byte [rdi + r8]
    PRINT_CHAR rax
.ret:
    ret


loop_start_sub:
    cmp al, '['
    sete cl
    jne .ret
    cmp byte [rdi + r8], 0
    jne .cont
    mov r10, 1
    jmp .ret
.cont:
    mov [rbp + r9*8], rsi
    inc r9
.ret:
    ret


loop_end_sub:
    cmp al, ']'
    sete cl
    jne .ret
    cmp byte [rdi + r8], 0
    je .finish
    mov rsi, [rbp + (r9-1)*8]
    jmp .ret
.finish:
    dec r9
.ret:
    ret