SingOS/lib/string.nasm

BITS 16 
; Compares two strings
; IN si: the first (zero terminated) string
; IN di: the second (zero terminated) string
; OUT SF and ZF (same semantics as cmp)
stringcompare:
    push bx
    push si
    push di
.loop:
    mov bl, [si]
    mov bh, [di]
    cmp bl, bh
    jne .end
    test bl, bl     ; bl and bh are the same, so bl = 0 => dl = 0
    jz .end
    inc si
    inc di
    jmp .loop
.end:
    pop di
    pop si
    pop bx

    ret

zstring_to_integer: 
    ;IN: si Pointer to string 
    ;OUT: ax result in binary
    push bx
    push si
    push cx
    push dx
    xor ax, ax
    xor bx, bx
    xor cx, cx
    xor dx, dx
    mov bx, 10
.loop:
    mov cl, [si]
    cmp cl, 0
    je .end
    sub cl,'0'
    cmp cl, 9
    ja .end ; next number is not a number, or its a zero, and then we are done
    ; multiply by 10, and add the new number.
    mul bx
    add ax, cx 
    inc si
    jmp .loop

.end:
    pop dx
    pop cx
    pop si 
    pop bx    
    ret