Category : Assembly Language Source Code
Archive   : ZENASM.ZIP
Filename : LST11-23.ASM

;
; *** Listing 11-23 ***
;
; Compares two word-sized arrays of equal length to see
; whether they differ, and if so, where, using non-string
; instructions.
;
jmp Skip
;
WordArray1 dw 100 dup (1), 0, 99 dup (2)
ARRAY_LENGTH_IN_WORDS equ (($-WordArray1)/2)
WordArray2 dw 100 dup (1), 100 dup (2)
;
; Returns pointers to the first locations at which two
; word-sized arrays of equal length differ, or zero if
; they're identical.
;
; Input:
; CX = length of the arrays (they must be of equal
; length)
; DS:SI = the first array to compare
; ES:DI = the second array to compare
;
; Output:
; DS:SI = pointer to the first differing location in
; the first array if there is a difference,
; or SI=0 if the arrays are identical
; ES:DI = pointer to the first differing location in
; the second array if there is a difference,
; or DI=0 if the arrays are identical
;
; Registers altered: AX, SI, DI
;
; Note: Does not handle arrays that are longer than 32K
; words or cross segment boundaries.
;
FindFirstDifference:
jcxz FindFirstDifferenceSame
;if there's nothing to
; check, we'll consider the
; arrays to be the same
FindFirstDifferenceLoop:
mov ax,[si]
cmp es:[di],ax ;compare the next two words
jnz FindFirstDifferenceFound ;the arrays differ
inc si
inc si ;point to the next words to
inc di ; compare
inc di
loop FindFirstDifferenceLoop ;the arrays are the
; same so far
FindFirstDifferenceSame:
sub si,si ;indicate that the strings
mov di,si ; are identical
FindFirstDifferenceFound:
ret
;
Skip:
call ZTimerOn
mov si,offset WordArray1 ;point to the two
mov di,ds ; arrays to be
mov es,di ; compared
mov di,offset WordArray2
mov cx,ARRAY_LENGTH_IN_WORDS
;# of words to check
call FindFirstDifference ;see if they differ
call ZTimerOff