;;  MASM syntax assembly language
;;
;;  Module: string compare
;;  Author: Lin Jensen
;;  Date:   25 Nov. 2002
;;
;;  Class example for csc116

;; C-convention, args pushed right to left, caller cleans up stack

        .386
        .model flat     ; sensible 32-bit code
        .code

public  strcmp          ; make a global symbol

strcmp:                 ; (char* str1, char* str2)
        push    ebp     ;save frame pointer
        mov     ebp, esp
        mov     esi, 8[ebp]     ; esi = str1 (pointer)
        mov     edi, 12[ebp]    ; edi = str2 (pointer)
;; WHILE characters equal and not end of string,
scloop:
        mov     al, [esi]       ; *str1 (char of first string)
        mov     bl, [edi]       ; *str2
        sub     al, bl          ; difference, al - bl
        jne     scdone          ; if different, return difference
           cmp    bl,0          ; if at end of (both) strings
           jz     scdone        ; al will be 0, return as meaning equal
           inc  esi             ; ELSE
           inc  edi             ;       increment both pointers
           jmp    scloop
scdone:
        cbw
        cwd                     ; sign extend result to 32 bits (eax)
        mov     esp, ebp
        pop     ebp             ; restore frame pointer
        ret                     ; return

        ; eax < 0 means str1 < str2
        ; eax = 0 means str1 = str2
        ; eax > 0 means str1 > str2

end             ;of assembling this file.