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page ,132 title strchr - search string for given character;***;strchr.asm - search a string for a given character;; Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.;;Purpose:; defines strchr() - search a string for a character;;Revision History:; 10-27-83 RN initial version; 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...; 09-08-94 GJF Smaller and faster.; 11-28-95 GJF Much faster version from Intel.; 06-12-01 PML inc->add 1, dec->sub 1 for Pentium 4 perf (vs7#267015);;*******************************************************************************
.xlist include cruntime.inc .list
page;***;char *strchr(string, chr) - search a string for a character;;Purpose:; Searches a string for a given character, which may be the; null character '\0'.;; Algorithm:; char *; strchr (string, chr); char *string, chr;; {; while (*string && *string != chr); string++;; if (*string == chr); return(string);; return((char *)0);; };;Entry:; char *string - string to search in; char chr - character to search for;;Exit:; returns pointer to the first occurence of c in string; returns NULL if chr does not occur in string;;Uses:;;Exceptions:;;*******************************************************************************
CODESEG
found_bx: lea eax,[edx - 1] pop ebx ; restore ebx ret ; _cdecl return
align 16 public strchr, __from_strstr_to_strchrstrchr proc
.FPO ( 0, 2, 0, 0, 0, 0 )
xor eax,eax mov al,[esp + 8] ; al = chr (search char)
__from_strstr_to_strchr label proc
push ebx ; PRESERVE EBX mov ebx,eax ; ebx = 0/0/0/chr shl eax,8 ; eax = 0/0/chr/0 mov edx,[esp + 8] ; edx = buffer test edx,3 ; test if string is aligned on 32 bits jz short main_loop_start
str_misaligned: ; simple byte loop until string is aligned mov cl,[edx] add edx,1 cmp cl,bl je short found_bx test cl,cl jz short retnull_bx test edx,3 ; now aligned ? jne short str_misaligned
main_loop_start: ; set all 4 bytes of ebx to [chr] or ebx,eax ; ebx = 0/0/chr/chr push edi ; PRESERVE EDI mov eax,ebx ; eax = 0/0/chr/chr shl ebx,10h ; ebx = chr/chr/0/0 push esi ; PRESERVE ESI or ebx,eax ; ebx = all 4 bytes = [chr]
; in the main loop (below), we are looking for chr or for EOS (end of string)
main_loop: mov ecx,[edx] ; read dword (4 bytes) mov edi,7efefeffh ; work with edi & ecx for looking for chr
mov eax,ecx ; eax = dword mov esi,edi ; work with esi & eax for looking for EOS
xor ecx,ebx ; eax = dword xor chr/chr/chr/chr add esi,eax
add edi,ecx xor ecx,-1
xor eax,-1 xor ecx,edi
xor eax,esi add edx,4
and ecx,81010100h ; test for chr jnz short chr_is_found ; chr probably has been found
; chr was not found, check for EOS
and eax,81010100h ; is any flag set ?? jz short main_loop ; EOS was not found, go get another dword
and eax,01010100h ; is it in high byte? jnz short retnull ; no, definitely found EOS, return failure
and esi,80000000h ; check was high byte 0 or 80h jnz short main_loop ; it just was 80h in high byte, go get ; another dwordretnull: pop esi pop ediretnull_bx: pop ebx xor eax,eax ret ; _cdecl return
chr_is_found: mov eax,[edx - 4] ; let's look one more time on this dword cmp al,bl ; is chr in byte 0? je short byte_0 test al,al ; test if low byte is 0 je retnull cmp ah,bl ; is it byte 1 je short byte_1 test ah,ah ; found EOS ? je retnull shr eax,10h ; is it byte 2 cmp al,bl je short byte_2 test al,al ; if in al some bits were set, bl!=bh je retnull cmp ah,bl je short byte_3 test ah,ah jz retnull jmp short main_loop ; neither chr nor EOS found, go get ; another dwordbyte_3: pop esi pop edi lea eax,[edx - 1] pop ebx ; restore ebx ret ; _cdecl return
byte_2: lea eax,[edx - 2] pop esi pop edi pop ebx ret ; _cdecl return
byte_1: lea eax,[edx - 3] pop esi pop edi pop ebx ret ; _cdecl return
byte_0: lea eax,[edx - 4] pop esi ; restore esi pop edi ; restore edi pop ebx ; restore ebx ret ; _cdecl return
strchr endp end
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