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page ,132
title strncmp - compare first n chars of two strings
;***
;strncmp.asm - compare first n characters of two strings
;
; Copyright (c) 1985-1991, Microsoft Corporation. All rights reserved.
;
;Purpose:
; defines strncmp() - compare first n characters of two strings
; for lexical order.
;
;Revision History:
; 10-26-83 RN initial version
; 05-18-88 SJM Add model-independent (large model) ifdef
; 08-04-88 SJM convert to cruntime/ add 32-bit support
; 08-23-88 JCR 386 cleanup
; 10-26-88 JCR General cleanup for 386-only code
; 03-23-90 GJF Changed to _stdcall. Also, fixed the copyright.
; 05-10-91 GJF Back to _cdecl, sigh...
;
;*******************************************************************************
.xlist
include cruntime.inc
.list
page
;***
;int strncmp(first, last, count) - compare first count chars of strings
;
;Purpose:
; Compares two strings for lexical order. The comparison stops
; after: (1) a difference between the strings is found, (2) the end
; of the strings is reached, or (3) count characters have been
; compared.
;
; Algorithm:
; int
; strncmp (first, last, count)
; char *first, *last;
; unsigned count;
; {
; if (!count)
; return(0);
; while (--count && *first && *first == *last)
; {
; first++;
; last++;
; }
; return(*first - *last);
; }
;
;Entry:
; char *first, *last - strings to compare
; unsigned count - maximum number of characters to compare
;
;Exit:
; returns <0 if first < last
; returns 0 if first == last
; returns >0 if first > last
;
;Uses:
;
;Exceptions:
;
;*******************************************************************************
CODESEG
public strncmp
strncmp proc \
uses edi esi ebx, \
first:ptr byte, \
last:ptr byte, \
count:IWORD
mov ecx,[count] ; cx=max number of bytes to compare
jecxz short toend ; it's as if strings are equal
mov ebx,ecx ; bx saves count
mov edi,[first] ; di=first pointer (es=segment part)
mov esi,edi ; si saves first pointer
xor eax,eax ; ax=0
repne scasb ; count bytes
neg ecx ; cx=count - strlen
add ecx,ebx ; strlen + count - strlen
okay:
mov edi,esi ; restore first pointer
mov esi,[last] ; si = last pointer
repe cmpsb ; compare strings
mov al,[esi-1]
xor ecx,ecx ; set return value = 0
cmp al,[edi-1] ; last-first
ja short lastbig ; <last is bigger>
je short toend ; <equal>
;jb short firstbig ; <first is bigger>
firstbig:
dec ecx ; first string is bigger
dec ecx ; make FFFE so 'not' will give 0001
lastbig: ; last string is bigger
not ecx ; return -1
toend:
mov eax,ecx ; return value
ifdef _STDCALL_
ret 2*DPSIZE + ISIZE ; _stdcall return
else
ret ; _cdecl return
endif
strncmp endp
end
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