CRT源码-字符串处理

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目录:
C/C++

CRT的 源码分为3部分:

  1. c C语言
  2. cpp c++
  3. 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 */
  • }
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 );
  • }
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
        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 );
  • }
size_t __cdecl strlen (
        const char * str
        )
{
        const char *eos = str;

        while( *eos++ ) ;

        return( eos - str - 1 );
}
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