|
|
page ,132 title strstr - search for one string inside another;***;strstr.asm - search for one string inside another;; Copyright (c) 1985-2001, Microsoft Corporation. All rights reserved.;;Purpose:; defines strstr() - search for one string inside another;;Revision History:; 02-02-88 SKS Rewritten from scratch. Now works correctly with; strings > 32 KB in length. Also smaller and faster.; 03-01-88 SKS Ensure that ES = DS right away (Small/Medium models); 05-18-88 SJM Add model-independent (large model) ifdef; 08-04-88 SJM convert to cruntime/ add 32-bit support; 08-18-88 PHG Corrected return value when src is empty string; to conform with ANSI.; 08-23-88 JCR Minor 386 cleanup; 10-26-88 JCR General cleanup for 386-only code; 03-26-90 GJF Changed to _stdcall. Also, fixed the copyright.; 05-10-91 GJF Back to _cdecl, sigh...; 12-19-94 GJF Revised to improve performance a bit.; 12-04-95 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 *strstr(str1, str2) - search for str2 in str1;;Purpose:; finds the first occurrence of str2 in str1;;Entry:; char *str1 - string to search in; char *str2 - string to search for;;Exit:; returns a pointer to the first occurrence of string2 in; string1, or NULL if string2 does not occur in string1;;Uses:;;Exceptions:;;*******************************************************************************
__from_strstr_to_strchr proto
CODESEG
public strstr
strstr proc
mov ecx,[esp + 8] ; str2 (the string to be searched for)
push edi ; Preserve edi, ebx and esi push ebx push esi
mov dl,[ecx] ; dl contains first char from str2
mov edi,[esp + 10h] ; str1 (the string to be searched)
test dl,dl ; is str2 empty? jz empty_str2
mov dh,[ecx + 1] ; second char from str2 test dh,dh ; is str2 a one-character string? jz strchr_call ; if so, go use strchr code
; length of str2 is now known to be > 1 (used later); dl contains first char from str2; dh contains second char from str2; edi holds str1
findnext: mov esi,edi ; esi = edi = pointers to somewhere in str1 mov ecx,[esp + 14h] ; str2
;use edi instead of esi to eliminate AGI mov al,[edi] ; al is next char from str1
add esi,1 ; increment pointer into str1
cmp al,dl je first_char_found
test al,al ; end of str1? jz not_found ; yes, and no match has been found
loop_start: mov al,[esi] ; put next char from str1 into al add esi,1 ; increment pointer in str1in_loop: cmp al,dl je first_char_found
test al,al ; end of str1? jnz loop_start ; no, go get another char from str1
not_found: pop esi pop ebx pop edi xor eax,eax ret
; recall that dh contains the second char from str2
first_char_found: mov al,[esi] ; put next char from str1 into al add esi,1
cmp al,dh ; compare second chars jnz in_loop ; no match, continue search
two_first_chars_equal: lea edi,[esi - 1] ; store position of last read char in str1
compare_loop: mov ah,[ecx + 2] ; put next char from str2 into ah test ah,ah ; end of str2? jz match ; if so, then a match has been found
mov al,[esi] ; get next char from str1 add esi,2 ; bump pointer into str1 by 2
cmp al,ah ; are chars from str1 and str2 equal? jne findnext ; no
; do one more iteration
mov al,[ecx + 3] ; put the next char from str2 into al test al,al ; end of str2 jz match ; if so, then a match has been found
mov ah,[esi - 1] ; get next char from str1 add ecx,2 ; bump pointer in str1 by 2 cmp al,ah ; are chars from str1 and str2 equal? je compare_loop
; no match. test some more chars (to improve execution time for bad strings).
jmp findnext
; str2 string contains only one character so it's like the strchr functioin
strchr_call: xor eax,eax pop esi pop ebx pop edi mov al,dl jmp __from_strstr_to_strchr
;;; Match! Return (ebx - 1);match: lea eax,[edi - 1] pop esi pop ebx pop edi ret
empty_str2: ; empty target string, return src (ANSI mandated) mov eax,edi pop esi pop ebx pop edi ret
strstr endp end
|
