xv6/string.c

#include "types.h"
#include "x86.h"

void* memset(void *dst, int c, uint n) {
    if ((int)dst % 4 == 0 && n % 4 == 0) {
        c &= 0xFF;
        stosl(dst, (c << 24) | (c << 16) | (c << 8) | c, n / 4);
    }
    else {
        stosb(dst, c, n);
    }
    return dst;
}

int memcmp(const void *v1, const void *v2, uint n) {
    const uchar *s1, *s2;

    s1 = v1;
    s2 = v2;
    while (n-- > 0) {
        if (*s1 != *s2) {
            return *s1 - *s2;
        }
        s1++, s2++;
    }

    return 0;
}

void* memmove(void *dst, const void *src, uint n) {
    const char *s;
    char *d;

    s = src;
    d = dst;
    if (s < d && s + n > d) {
        s += n;
        d += n;
        while (n-- > 0) {
            *--d = *--s;
        }
    }
    else {
        while (n-- > 0) {
            *d++ = *s++;
        }
    }

    return dst;
}

// memcpy exists to placate GCC.  Use memmove.
void* memcpy(void *dst, const void *src, uint n) {
    return memmove(dst, src, n);
}

int strncmp(const char *p, const char *q, uint n) {
    while (n > 0 && *p && *p == *q) {
        n--, p++, q++;
    }
    if (n == 0) {
        return 0;
    }
    return (uchar) * p - (uchar) * q;
}

char* strncpy(char *s, const char *t, int n) {
    char *os;

    os = s;
    while (n-- > 0 && (*s++ = *t++) != 0) {
        ;
    }
    while (n-- > 0) {
        *s++ = 0;
    }
    return os;
}

// Like strncpy but guaranteed to NUL-terminate.
char* safestrcpy(char *s, const char *t, int n) {
    char *os;

    os = s;
    if (n <= 0) {
        return os;
    }
    while (--n > 0 && (*s++ = *t++) != 0) {
        ;
    }
    *s = 0;
    return os;
}

int strlen(const char *s) {
    int n;

    for (n = 0; s[n]; n++) {
        ;
    }
    return n;
}