mirror of https://github.com/tongzx/nt5src
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
138 lines
3.4 KiB
138 lines
3.4 KiB
page ,132
|
|
title strlen - return the length of a null-terminated string
|
|
;***
|
|
;strlen.asm - contains strlen() routine
|
|
;
|
|
; Copyright (c) 1985-2001, 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...
|
|
; 04-23-93 GJF Tuned for the 486.
|
|
; 06-16-93 GJF Added .FPO directive.
|
|
; 11-28-94 GJF New, faster version from Intel.
|
|
; 11-28-95 GJF Align main_loop on para boundary for 486 and P6
|
|
;
|
|
;*******************************************************************************
|
|
|
|
.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:
|
|
; EAX = length of the string "str", exclusive of the final null byte
|
|
;
|
|
;Uses:
|
|
; EAX, ECX, EDX
|
|
;
|
|
;Exceptions:
|
|
;
|
|
;*******************************************************************************
|
|
|
|
CODESEG
|
|
|
|
public strlen
|
|
|
|
strlen proc
|
|
|
|
.FPO ( 0, 1, 0, 0, 0, 0 )
|
|
|
|
string equ [esp + 4]
|
|
|
|
mov ecx,string ; ecx -> string
|
|
test ecx,3 ; test if string is aligned on 32 bits
|
|
je short main_loop
|
|
|
|
str_misaligned:
|
|
; simple byte loop until string is aligned
|
|
mov al,byte ptr [ecx]
|
|
inc ecx
|
|
test al,al
|
|
je short byte_3
|
|
test ecx,3
|
|
jne short str_misaligned
|
|
|
|
add eax,dword ptr 0 ; 5 byte nop to align label below
|
|
|
|
align 16 ; should be redundant
|
|
|
|
main_loop:
|
|
mov eax,dword ptr [ecx] ; read 4 bytes
|
|
mov edx,7efefeffh
|
|
add edx,eax
|
|
xor eax,-1
|
|
xor eax,edx
|
|
add ecx,4
|
|
test eax,81010100h
|
|
je short main_loop
|
|
; found zero byte in the loop
|
|
mov eax,[ecx - 4]
|
|
test al,al ; is it byte 0
|
|
je short byte_0
|
|
test ah,ah ; is it byte 1
|
|
je short byte_1
|
|
test eax,00ff0000h ; is it byte 2
|
|
je short byte_2
|
|
test eax,0ff000000h ; is it byte 3
|
|
je short byte_3
|
|
jmp short main_loop ; taken if bits 24-30 are clear and bit
|
|
; 31 is set
|
|
|
|
byte_3:
|
|
lea eax,[ecx - 1]
|
|
mov ecx,string
|
|
sub eax,ecx
|
|
ret
|
|
byte_2:
|
|
lea eax,[ecx - 2]
|
|
mov ecx,string
|
|
sub eax,ecx
|
|
ret
|
|
byte_1:
|
|
lea eax,[ecx - 3]
|
|
mov ecx,string
|
|
sub eax,ecx
|
|
ret
|
|
byte_0:
|
|
lea eax,[ecx - 4]
|
|
mov ecx,string
|
|
sub eax,ecx
|
|
ret
|
|
|
|
strlen endp
|
|
|
|
end
|