windows-nt/Source/XPSP1/NT/base/crts/crtw32/string/i386/strstr.asm

184 lines
5.3 KiB
NASM
Raw Permalink Normal View History

2020-09-26 03:20:57 -05:00
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.
;
;*******************************************************************************
.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
inc esi ; 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
inc esi ; increment pointer in str1
in_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
inc esi
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