Category : Assembly Language Source Code
Archive   : RHSTDLIB.ZIP
Filename : STRCMP.ASM

stdlib segment para public 'slcode'
assume cs:stdlib
;
;
; strcmp- Compares two strings.
;
; inputs:
;
; es:di- First string (The string to compare)
; dx:si- Second string (The string to compare against)
;
; e.g.,
; "if (es:di < dx:si) then ..."
;
; returns:
;
; cx- index into strings where they differ (points at the zero byte
; if the two strings are equal).
;
; Condition codes set according to the string comparison. You should
; use the unsigned branches (ja, jb, je, etc.) after calling this
; routine.
;
public sl_strcmp
;
sl_strcmp proc far
push es
push ds
push bx
push ax
push si
push di
;
; Swap pointers so they're more convenient for the LODSB/SCASB instrs.
;
xchg si, di
mov ax, es
mov ds, ax
mov es, dx
;
xor bx, bx ;Set initial index to zero.
;
; In order to preserve the direction flag across this call, we have to
; test whether or not it is set here and execute two completely separate
; pieces of code (so we know which state to exit in. Unfortunately, we
; cannot use pushf to preserve this flag since we need to return status
; info in the other flags.
;
pushf
pop ax
test ah, 4 ;Test direction bit.
jnz DirIsSet
sclp: lodsb
scasb
jne scNE ;If strings are <>, quit.
inc bx ;Increment index into strs.
cmp al, 0 ;Check for end of strings.
jne sclp
pushf
dec bx
popf
;
scNE: pop di
pop si
mov cx, bx
pop bx
pop ax
pop ds
pop es
ret ;Return with direction flag clear.
;
;
DirIsSet: lodsb
scasb
jne scNE2 ;If strings are <>, quit.
inc bx
cmp al, 0 ;Check for end of strings.
jne DirIsSet
pushf
dec bx
popf
;
scNE2: pop di
pop si
mov cx, bx
pop bx
pop ax
pop ds
pop es
std ;Return with direction flag set.
ret

sl_strcmp endp
;
;
stdlib ends
end