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


char *strpbrk(const char *s1, const char *s2)
{
    while(*s1)
        if(strchr(s2, *s1++))
            return (char*)--s1;
    return 0;
}


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


int strspn_custom(const char *p, const char *s)
{
    int i, j;

    for (i = 0; p[i]; i++) {
        for (j = 0; s[j]; j++) {
            if (s[j] == p[i])
                break;
        }
        if (!s[j])
            break;
    }
    return (i);
}

char * strtok(char *s1, const char *delimit)
{
    static char *lastToken = NULL; /* UNSAFE SHARED STATE! */
    char *tmp;

    /* Skip leading delimiters if new string. */
    if ( s1 == NULL ) {
        s1 = lastToken;
        if (s1 == NULL)         /* End of story? */
            return NULL;
    } else {
        s1 += strspn_custom(s1, delimit);
    }

    /* Find end of segment */
    tmp = strpbrk(s1, delimit);
    if (tmp) {
        /* Found another delimiter, split string and save state. */
        *tmp = '\0';
        lastToken = tmp + 1;
    } else {
        /* Last segment, remember that. */
        lastToken = NULL;
    }

    return s1;
}