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

stdlib segment para public 'slcode'
assume cs:stdlib
;
;
; strcmpl- Compares the string pointed at by es:si to the string following
; the call instruction.
;
; inputs:
;
; es:di- First string (The string to compare)
; cs:rtn- Second string (The string to compare against)
;
; e.g.,
; "if (es:si < cs:rtn) 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_strcmpl
;
sl_strcmpl proc far
push bp
mov bp, sp
push es
push ds
push cx
push si
push di
mov ax, es
mov ds, ax
mov si, di
les di, 2[bp]
;
; 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
;
; Compute the length of the string following the CALL instruction:
;
cld
mov al, 0
mov cx, 0ffffh
repne scasb
xchg di, 2[bp] ;Save as new return address.
neg cx
dec cx ;Length of string.
mov ax, cx
repe cmpsb ;Compare the two strings.
;
pushf
sub ax, cx
dec ax
popf
pop di
pop si
pop cx
pop ds
pop es
pop bp
ret ;Return with direction flag clear.
;
;
DirIsSet: cld
mov al, 0
mov cx, 0ffffh
repne scasb
xchg di, 2[bp] ;Save as new return address.
neg cx
dec cx ;Length of string.
mov ax, cx
repe cmpsb ;Compare the two strings.
;
pushf
sub ax, cx
dec ax
popf
pop di
pop si
pop cx
pop ds
pop es
pop bp
std
ret ;Return with direction flag set.
;
;
;
sl_strcmpl endp
;
;
stdlib ends
end