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page ,132
title memchr - search memory for a given character
;***
;memchr.asm - search block of memory for a given character
;
; Copyright (c) 1985-1991, Microsoft Corporation. All rights reserved.
;
;Purpose:
; defines memchr() - search memory until a character is
; found or a limit is reached.
;
;Revision History:
; 05-16-84 RN initial version
; 07-20-87 SKS rewritten for speed
; 05-17-88 SJM Add model-independent (large model) ifdef
; 08-04-88 SJM convert to cruntime/ add 32-bit support
; 08-23-88 JCR 386 cleanup
; 10-25-88 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
;***
;char *memchr(buf, chr, cnt) - search memory for given character.
;
;Purpose:
; Searched at buf for the given character, stopping when chr is
; first found or cnt bytes have been searched through.
;
; Algorithm:
; char *
; memchr (buf, chr, cnt)
; char *buf;
; int chr;
; unsigned cnt;
; {
; while (cnt && *buf++ != c)
; cnt--;
; return(cnt ? --buf : NULL);
; }
;
;Entry:
; char *buf - memory buffer to be searched
; char chr - character to search for
; unsigned cnt - max number of bytes to search
;
;Exit:
; returns pointer to first occurence of chr in buf
; returns NULL if chr not found in the first cnt bytes
;
;Uses:
;
;Exceptions:
;
;*******************************************************************************
CODESEG
public memchr
memchr proc \
buf:ptr, \
chr:byte, \
cnt:IWORD
xor eax,eax ; return NULL if cnt == 0
mov ecx,(cnt) ; cx = count
jecxz short empty
push edi ; Preserve DI
mov edi,buf ; di = buffer
mov al,chr ; al = search char
repne scasb ; scan for byte
mov eax,0 ; assume not found (ax=NULL)
jne short done ; not found -- return NULL
lea eax,[edi-1] ; found - return address of matching byte
done:
pop edi ; Restore DI
empty:
ifdef _STDCALL_
ret DPSIZE + 2*ISIZE ; _stdcall return
else
ret ; _cdecl return
endif
memchr endp
end
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