一些常用的C函数实现（转）

来自http://blog.chinaunix.net/u3/107272/showart.php?id=2135346，谢谢该网友分享……

搞嵌入式开发的时候，为了节省存储资源，只想用到几个函数，于是不用动用stdio/stdlib，大家可以自己积累一些常用函数的简单实现办法<这些来自于伟大的网，可惜忘了是从哪位神那儿偷来的，实在抱歉>：  //定义一个宏，比较两个数a、b的大小，不能使用大于、小于、if语句
#define max(a,b) (abs(a-b)-(a-b))?b:a

int strcmp2(const char *s1, const char*s2)
{
    int ret;
    for( ; *s1++==*s2++; ret=*s1-*s2 )
    {
        if(*s1=='\0')
            break;
    }
    if(ret<0)
        ret = -1;
    else if(ret>0)
        ret = 1;

    return ret;
}

int strcmp3( char *src, char *sub )
{
    int ret;
    while( !(ret=*src -*sub) && *sub )
    {
        ++src;
        ++sub;
    }
    if(ret<0)
        ret = -1;
    else if(ret>0)
        ret = 1;

    return ret;
}

char *strncpy2( char *dest, const char *src, size_t count )
{
    char *str=dest;
    for( ; (count>0)&&(*dest=*src); count--,dest++,src++ )
        ;
    return str;
}

char * strncpy1( char *dest, const char *src, size_t count )
{
    char *address = dest;
    assert( (dest!=NULL && src!=NULL && count>1) );
    while( count-->0 && (*dest++ = *src++)!='\0' );
    return address;
}

char * strcpy1( char *strDest, const char *strSrc )

{
    char *address = strDest;
    assert( (strDest != NULL) && (strSrc != NULL) );

    printf("1=%s 2=%s\n", strDest, strSrc);
    while( (*strDest++ = * strSrc++)!='\0' )
    {
        printf("1=%s 2=%s\n", strDest, strSrc);
    }

    printf("function str=%s\n", address);
    return address;
}

int strlen1( const char *str ) //输入参数const

{
    int len=0;
    assert( str != NULL ); //断言字符串地址非0



    while( (*str++) != '\0' )
    {
        printf("len=%d str=%s\n", len, str);
        len++;
    }

    printf("\n\nlen=%d str=%s\n", len, str);
    return len;

}


int strlen2( const char *src )
{
    int len=0;
    assert( src!=NULL );
    while( *src++!='\0' )
    {
        len++;
    }
    return len;
}

int mystrlen( const char *p)
{
    int t;
        printf("p=[%s]\n", p);
        if(*p)
        {
            t = mystrlen(p+1)+1;
                printf("t=%d\n",t);
                
                return t;
        }
    printf("last!!!!!!!!\n");
        return 0;
}

int mystrlen1( const char *p)
{
    printf("\nfirst=0x%x last=0x%x\n", p, strchr(p,'\0') );
    return strchr(p,'\0')-p;
}

int mystrlen2( const char *p)
{
    return (printf("%s",p));
}

int mystrlen3( const char *p)
{
    if( 0==p[0] ) return 0;
    if( 0==p[1] ) return 1;
    if( 0==p[2] ) return 2;
    if( 0==p[3] ) return 3;
    for(*(int*)p=4;'\0'!=p[*(int*)p]; ++(*(int*)p))
    {
    }
    return *(int*)p;
}


int x(int n)
{
    if(n<=3)
    {
        printf("laset n=%d\n", n);
        return 1;
    }
    else
    {
        printf("n=%d \n", n);
        return x(n-2)+x(n-4)+1;
    }
}


int calcone(unsigned char s)
{
    int ret=0;
    while (s)
    {
        ret++;
        s&=s-1;
    }
    return ret;
}

size_t func( unsigned char x )
{
    printf("0x=0x%x >>1=0x%x\n",x, x>>1);
    x = (x & 0x55) + ((x>>1) & 0x55);
    printf("0x=0x%x >>2=0x%x\n",x, x>>2);
    x = (x & 0x33) + ((x>>2) & 0x33);
    printf("0x33=0x%x\n",x);
    x = (x & 0x0f) + ((x>>4) & 0x0f);
    printf("0x0f=0x%x\n",x);
    return x;
}

int MaxSub(const int A[], int N)
{
    int ThisSum=0;
    int MaxSum=0;
    int i;

    for(i=0;i<N;i++)
    {
        ThisSum += A[i];

        if(ThisSum > MaxSum)
            MaxSum = ThisSum;
        else if(ThisSum < 0)
            ThisSum = 0;
    }
    return MaxSum;
}

void shuzu( int a[], int b[][2] )
{
    printf("a=%d b=%d!\n", a[0], b[0][0]);
    return;
}


int count(int n)
{
    if(1==n)
    {
        printf("1\n");
        return 1;
    }
    else if(2==n)
    {
        printf("2\n");
        return 2;
    }
    else
    {
        printf("%d%d%d\n", n, n, n);
        return count(n-1)+count(n-2);
    }
}


char * ReverseStringSlow(char * aStr)
{
    int i,j;
    int len = strlen(aStr);
    char * ptemp = (char*) malloc (len);
    for ( i = len - 1, j = 0; i >= 0; --i, ++j)
    {
        ptemp[j] = aStr[i];
    }
    strncpy(aStr, ptemp, len);
    free(ptemp);
    return aStr;
}


char * ReverseStringFast(char * aStr)
{
    int i;
    int len = strlen(aStr);
    char temp = '\0';
    for( i = 0; i < len/2; ++i)
    {
        printf("i=%d len-i-1=%d\n", i, len-i-1);
        temp = aStr[i];
        aStr[i] = aStr[len-i-1];
        aStr[len-i-1] = temp;
    }
    return aStr;
}