如何优化这个自写的strcmp函数
老师讲，还可以进一步优化，请各位指点一下思路
int my_strcmp(const char *s1, const char *s2){ while(*s1 == *s2){ if(*s1 == '\0'){ return 0; } s1++; s2++; } return *s1 - *s2; } 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 .listpage;***;strcmp - compare two strings, returning less than, equal to, or greater than;;Purpose:; Compares two string, determining their lexical order. Unsigned; comparison is used.;; Algorithm:; int strcmp ( src , dst ); unsigned char *src;; unsigned char *dst;; {; int ret = 0 ;;; while( ! (ret = *src - *dst) && *dst); ++src, ++dst;;; if ( ret < 0 ); ret = -1 ;; else if ( ret > 0 ); ret = 1 ;;; return( ret );; };;Entry:; const char * src - string for left-hand side of comparison; const char * dst - string for right-hand side of comparison;;Exit:; AX < 0, 0, or >0, indicating whether the first string is; Less than, Equal to, or Greater than the second string.;;Uses:; CX, DX;;Exceptions:;;******************************************************************************* CODESEG public strcmpstrcmp proc \ str1:ptr byte, \ str2:ptr byte OPTION PROLOGUE:NONE, EPILOGUE:NONE .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 4dodwords: mov eax,[edx] cmp al,[ecx] jne short donene or al,al jz short doneeq cmp ah,[ecx + 1] jne short donene or ah,ah jz short doneeq shr eax,16 cmp al,[ecx + 2] jne short donene or al,al jz short doneeq cmp ah,[ecx + 3] jne short donene add ecx,4 add edx,4 or ah,ah jnz short dodwords align 4doneeq: xor eax,eax ret align 4donene: ; The instructions below should place -1 in eax if src < dst, ; and 1 in eax if src > dst. sbb eax,eax sal eax,1 add eax,1 ret align 4dopartial: test edx,1 jz short doword mov al,[edx] add edx,1 cmp al,[ecx] jne short donene add ecx,1 or al,al jz short doneeq test edx,2 jz short dodwords align 4doword: mov ax,[edx] add edx,2 cmp al,[ecx] jne short donene or al,al jz short doneeq cmp ah,[ecx + 1] jne short donene or ah,ah jz short doneeq add ecx,2 jmp short dodwordsstrcmp endp end
[解决办法]
int my_strcmp(const char *s1, const char *s2){ while(*s1 == *s2){ // if(*s1 == '\0'){ 注释掉这3句，就是在你代码效率基础上进一步优化 // return 0; // } s1++; s2++; } return *s1 - *s2; } 也可以这样 int my_strcmp(const char *s1, const char *s2){ while （*s1++ == *s2++） { } return *s1 - *s2;}这是对你代码进行优化，第二个只是对代码进行精简。