windows-server-2003/base/crts/crtw32/string/i386/strncmp.asm

	page	,132
	title	strncmp - compare first n chars of two strings
;***
;strncmp.asm - compare first n characters of two strings
;
;	Copyright (c) 1985-2001, 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...
;       06-12-01  PML   inc->add 1, dec->sub 1 for Pentium 4 perf (vs7#267015)
;
;*******************************************************************************

	.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:			; first string is bigger
	sub	ecx,2		; 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