libc.c

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#include <stddef.h>

void *memcpy(void *dst, const void *src, size_t n)
{
    char *d = dst;
    const char *s = src;
 
    while (n--)
        *d++ = *s++;
 
    return dst;
}

void *memset(void *dst, int c, size_t n)
{
    char *d = dst;
 
    while (n--)
        *d++ = (char) c;
 
    return dst;
}

void *memmove(void *dst, const void *src, size_t n)
{
    char *d = dst;
    const char *s = src;
 
    if (d < s) {
        while (n--)
            *d++ = *s++;
    } else {
        while (n--)
            d[n] = s[n];
    }
 
    return dst;
}

int memcmp(const void *a, const void *b, size_t n)
{
    const unsigned char *x = a, *y = b;
 
    for (; n--; ++x, ++y)
        if (*x != *y)
            return *x - *y;
 
    return 0;
}