; strings.asm — string primitives: strlen, str_eq, str_copy
%include "include/syscall.inc"

section .text
global str_len
global str_eq
global str_copy

; size_t str_len(const char *s)
str_len:
    xor rax, rax
.loop:
    cmp byte [rdi+rax], 0
    je .done
    inc rax
    jmp .loop
.done:
    ret

; int str_eq(const char *a, const char *b) — returns 1 if equal, 0 if not
str_eq:
    push rbx
.loop:
    movzx rax, byte [rdi]
    movzx rbx, byte [rsi]
    cmp rax, rbx
    jne .not_eq
    test rax, rax
    je .equal
    inc rdi
    inc rsi
    jmp .loop
.equal:
    mov rax, 1
    pop rbx
    ret
.not_eq:
    xor rax, rax
    pop rbx
    ret

; void str_copy(char *dst, const char *src)
str_copy:
.loop:
    movzx rax, byte [rsi]
    mov [rdi], al
    test rax, rax
    je .done
    inc rdi
    inc rsi
    jmp .loop
.done:
    ret