200 lines
6 KiB
NASM
200 lines
6 KiB
NASM
page ,132
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title strchr - search string for given character
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;***
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;strchr.asm - search a string for a given character
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;
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; Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; defines strchr() - search a string for a character
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;
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;Revision History:
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; 10-27-83 RN initial version
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; 05-17-88 SJM Add model-independent (large model) ifdef
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; 08-04-88 SJM convert to cruntime/ add 32-bit support
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; 08-23-88 JCR 386 cleanup
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; 10-25-88 JCR General cleanup for 386-only code
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; 03-23-90 GJF Changed to _stdcall. Also, fixed the copyright.
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; 05-10-91 GJF Back to _cdecl, sigh...
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; 09-08-94 GJF Smaller and faster.
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; 11-28-95 GJF Much faster version from Intel.
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;
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;*******************************************************************************
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.xlist
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include cruntime.inc
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.list
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page
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;***
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;char *strchr(string, chr) - search a string for a character
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;
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;Purpose:
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; Searches a string for a given character, which may be the
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; null character '\0'.
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;
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; Algorithm:
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; char *
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; strchr (string, chr)
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; char *string, chr;
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; {
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; while (*string && *string != chr)
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; string++;
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; if (*string == chr)
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; return(string);
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; return((char *)0);
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; }
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;
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;Entry:
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; char *string - string to search in
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; char chr - character to search for
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;
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;Exit:
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; returns pointer to the first occurence of c in string
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; returns NULL if chr does not occur in string
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;
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;Uses:
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;
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;Exceptions:
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;
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;*******************************************************************************
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CODESEG
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found_bx:
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lea eax,[edx - 1]
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pop ebx ; restore ebx
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ret ; _cdecl return
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align 16
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public strchr, __from_strstr_to_strchr
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strchr proc
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.FPO ( 0, 2, 0, 0, 0, 0 )
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xor eax,eax
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mov al,[esp + 8] ; al = chr (search char)
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__from_strstr_to_strchr label proc
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push ebx ; PRESERVE EBX
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mov ebx,eax ; ebx = 0/0/0/chr
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shl eax,8 ; eax = 0/0/chr/0
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mov edx,[esp + 8] ; edx = buffer
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test edx,3 ; test if string is aligned on 32 bits
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jz short main_loop_start
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str_misaligned: ; simple byte loop until string is aligned
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mov cl,[edx]
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inc edx
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cmp cl,bl
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je short found_bx
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test cl,cl
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jz short retnull_bx
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test edx,3 ; now aligned ?
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jne short str_misaligned
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main_loop_start: ; set all 4 bytes of ebx to [chr]
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or ebx,eax ; ebx = 0/0/chr/chr
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push edi ; PRESERVE EDI
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mov eax,ebx ; eax = 0/0/chr/chr
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shl ebx,10h ; ebx = chr/chr/0/0
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push esi ; PRESERVE ESI
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or ebx,eax ; ebx = all 4 bytes = [chr]
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; in the main loop (below), we are looking for chr or for EOS (end of string)
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main_loop:
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mov ecx,[edx] ; read dword (4 bytes)
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mov edi,7efefeffh ; work with edi & ecx for looking for chr
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mov eax,ecx ; eax = dword
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mov esi,edi ; work with esi & eax for looking for EOS
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xor ecx,ebx ; eax = dword xor chr/chr/chr/chr
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add esi,eax
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add edi,ecx
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xor ecx,-1
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xor eax,-1
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xor ecx,edi
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xor eax,esi
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add edx,4
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and ecx,81010100h ; test for chr
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jnz short chr_is_found ; chr probably has been found
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; chr was not found, check for EOS
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and eax,81010100h ; is any flag set ??
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jz short main_loop ; EOS was not found, go get another dword
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and eax,01010100h ; is it in high byte?
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jnz short retnull ; no, definitely found EOS, return failure
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and esi,80000000h ; check was high byte 0 or 80h
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jnz short main_loop ; it just was 80h in high byte, go get
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; another dword
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retnull:
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pop esi
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pop edi
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retnull_bx:
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pop ebx
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xor eax,eax
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ret ; _cdecl return
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chr_is_found:
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mov eax,[edx - 4] ; let's look one more time on this dword
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cmp al,bl ; is chr in byte 0?
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je short byte_0
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test al,al ; test if low byte is 0
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je retnull
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cmp ah,bl ; is it byte 1
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je short byte_1
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test ah,ah ; found EOS ?
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je retnull
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shr eax,10h ; is it byte 2
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cmp al,bl
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je short byte_2
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test al,al ; if in al some bits were set, bl!=bh
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je retnull
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cmp ah,bl
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je short byte_3
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test ah,ah
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jz retnull
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jmp short main_loop ; neither chr nor EOS found, go get
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; another dword
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byte_3:
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pop esi
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pop edi
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lea eax,[edx - 1]
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pop ebx ; restore ebx
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ret ; _cdecl return
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byte_2:
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lea eax,[edx - 2]
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pop esi
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pop edi
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pop ebx
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ret ; _cdecl return
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byte_1:
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lea eax,[edx - 3]
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pop esi
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pop edi
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pop ebx
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ret ; _cdecl return
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byte_0:
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lea eax,[edx - 4]
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pop esi ; restore esi
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pop edi ; restore edi
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pop ebx ; restore ebx
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ret ; _cdecl return
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strchr endp
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end
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