string.c

#include <string.h>

int strncmp(const char *s1, const char *s2, size_t n)
{
     unsigned char uc1, uc2;
     /* Nothing to compare?  Return zero.  */
     if (n == 0)
         return 0;
     /* Loop, comparing bytes.  */
     while (n-- > 0 && *s1 == *s2) {
         /* If we've run out of bytes or hit a null, return zero
            since we already know *s1 == *s2.  */
         if (n == 0 || *s1 == '\0')
             return 0;
         s1++;
         s2++;
     }
     uc1 = (*(unsigned char *) s1);
     uc2 = (*(unsigned char *) s2);
     return ((uc1 < uc2) ? -1 : (uc1 > uc2));
}

char *strncpy(char *dest, const char *src, size_t n)
{
    char *ret = dest;
    do {
        if (!n--)
            return ret;
    } while ((*dest++ = *src++));
    while (n--)
        *dest++ = 0;
    return ret;
}
int strlen(const char *s)
{
    size_t i;
    for (i = 0; s[i] != '\0'; i++) ;
    return i;
}

char *strchr(const char *s, int c)
{
    while (*s != (char)c)
        if (!*s++)
            return 0;
    return (char *)s;
}

char *strcat(char *dest, const char *src)
{
    char *ret = dest;
    while (*dest)
        dest++;
    while ((*dest++ = *src++))
        ;
    return ret;
}

char *strcpy(char * dest, const char * src)
{
    char *ret = dest;
    while ((*dest++ = *src++))
        ;
    return ret;
}

void *memmove(void *dest, const void *src, size_t n)
{
    unsigned char *pd = dest;
    const unsigned char *ps = src;
    if (ps < pd)
        for (pd += n, ps += n; n--;)
            *--pd = *--ps;
    else
        while(n--)
            *pd++ = *ps++;
    return dest;
}

void *memset(void *s, int c, size_t n)
{
    unsigned char* p=s;
    while(n--)
        *p++ = (unsigned char)c;
    return s;
}

void *memcpy(void *dest, const void *src, size_t n)
{
    char *dp = dest;
    const char *sp = src;
    while (n--)
        *dp++ = *sp++;
    return dest;
}

int memcmp(const void *s1, const void *s2, size_t n)
 {
     const unsigned char *us1 = (const unsigned char *) s1;
     const unsigned char *us2 = (const unsigned char *) s2;
     while (n-- != 0) {
         if (*us1 != *us2)
             return (*us1 < *us2) ? -1 : +1;
         us1++;
         us2++;
     }
     return 0;
 }