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page ,132
title strlen - return the length of a null-terminated string
;***
;strlen.asm - contains strlen() routine
;
; Copyright (c) 1985-1991, Microsoft Corporation. All rights reserved.
;
;Purpose:
; strlen returns the length of a null-terminated string,
; not including the null byte itself.
;
;Revision History:
; 04-21-87 SKS Rewritten to be fast and small, added file header
; 05-18-88 SJM Add model-independent (large model) ifdef
; 08-02-88 SJM Add 32 bit code, use cruntime vs cmacros
; 08-23-88 JCR 386 cleanup
; 10-05-88 GJF Fixed off-by-2 error.
; 10-10-88 JCR Minor improvement
; 10-25-88 JCR General cleanup for 386-only code
; 10-26-88 JCR Re-arrange regs to avoid push/pop ebx
; 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
;***
;strlen - return the length of a null-terminated string
;
;Purpose:
; Finds the length in bytes of the given string, not including
; the final null character.
;
; Algorithm:
; int strlen (const char * str)
; {
; int length = 0;
;
; while( *str++ )
; ++length;
;
; return( length );
; }
;
;Entry:
; const char * str - string whose length is to be computed
;
;Exit:
; AX = length of the string "str", exclusive of the final null byte
;
;Uses:
; CX, DX
;
;Exceptions:
;
;*******************************************************************************
CODESEG
public strlen
strlen proc \
uses edi, \
string:ptr byte
mov edi,string ; edi -> string
xor eax,eax ; null byte
or ecx,-1 ; set ecx to -1
repne scasb ; scan for null, ecx = -(1+strlen(str))
not ecx
dec ecx ; ecx = strlen(str)
mov eax,ecx ; eax = strlen(str)
ifdef _STDCALL_
ret DPSIZE ; _stdcall return
else
ret ; _cdecl return
endif
strlen endp
end
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