CRT源码-字符串处理
CRT的 源码分为3部分:
- c C语言
- cpp c++
- asm 性能优化汇编版本
strcat
char * __cdecl strcat (
char * dst,
const char * src
)
{
char * cp = dst;
while( *cp )
cp++; /* find end of dst */
while( *cp++ = *src++ ) ; /* Copy src to end of dst */
return( dst ); /* return dst */
}
strcmp
int __cdecl strcmp (
const char * src,
const char * dst
)
{
int ret = 0 ;
while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
++src, ++dst;
if ( ret < 0 )
ret = -1 ;
else if ( ret > 0 )
ret = 1 ;
return( ret );
}
strcmp asm 版本
page ,132
title strcmp.asm - compare two strings
;***
;strcmp.asm - routine to compare two strings (for equal, less, or greater)
;
; Copyright (c) Microsoft Corporation. All rights reserved.
;
;Purpose:
; STRCMP compares two strings and returns an integer
; to indicate whether the first is less than the second, the two are
; equal, or whether the first is greater than the second, respectively.
; Comparison is done byte by byte on an UNSIGNED basis, which is to
; say that Null (0) is less than any other character (1-255).
;
;*******************************************************************************
.xlist
include cruntime.inc
.list
page
;***
;strcmp - compare two strings, returning less than, equal to, or greater than
;
;Purpose:
; Compares two string, determining their lexical order. Unsigned
; comparison is used.
;
; Base Algorithm:
; int strcmp ( const char *str1, const char *str2 )
; {
; const unsigned char *src1 = (const unsigned char *)str1;
; const unsigned char *src2 = (const unsigned char *)str2;
; int ret = 0 ;
;
; while( ! (ret = *src1 - *src2) && *src2)
; ++src1, ++src2;
;
; if ( ret < 0 )
; ret = -1 ;
; else if ( ret > 0 )
; ret = 1 ;
;
; return( ret );
; }
;
;Entry:
; const char * src1 - string for left-hand side of comparison
; const char * src2 - string for right-hand side of comparison
;
;Exit:
; EAX < 0, 0, or >0, indicating whether the first string is
; Less than, Equal to, or Greater than the second string.
;
;Uses:
; ECX, EDX
;
;Exceptions:
;
;*******************************************************************************
CODESEG
public strcmp
strcmp proc \
str1:ptr byte, \
str2:ptr byte
OPTION PROLOGUE:NONE, EPILOGUE:NONE
; .FPO (cdwLocals, cdwParams, cbProlog, cbRegs, fUseBP, cbFrame)
.FPO ( 0, 2, 0, 0, 0, 0 )
mov edx,[esp + 4] ; edx = src
mov ecx,[esp + 8] ; ecx = dst
test edx,3
jnz short dopartial
align 4
dodwords:
mov eax,[edx]
cmp al,[ecx]
jne short donene
test al,al
jz short doneeq
cmp ah,[ecx + 1]
jne short donene
test ah,ah
jz short doneeq
shr eax,16
cmp al,[ecx + 2]
jne short donene
test al,al
jz short doneeq
cmp ah,[ecx + 3]
jne short donene
add ecx,4
add edx,4
test ah,ah
jnz short dodwords
align 4
doneeq:
xor eax,eax
ret
align 8
donene:
; The instructions below should place -1 in eax if src < dst,
; and 1 in eax if src > dst.
sbb eax,eax
or eax,1
ret
align 16
dopartial:
test edx,1
jz short doword
mov al,[edx]
add edx,1
cmp al,[ecx]
jne short donene
add ecx,1
test al,al
jz short doneeq
test edx,2
jz short dodwords
align 4
doword:
mov ax,[edx]
add edx,2
cmp al,[ecx]
jne short donene
test al,al
jz short doneeq
cmp ah,[ecx + 1]
jne short donene
test ah,ah
jz short doneeq
add ecx,2
jmp short dodwords
strcmp endp
end
strlen
size_t __cdecl strlen (
const char * str
)
{
const char *eos = str;
while( *eos++ ) ;
return( eos - str - 1 );
}