Path component hashing

#define ONEBYTES        0x0101010101010101ul
#define SLASHBYTES      0x2f2f2f2f2f2f2f2ful
#define HIGHBITS        0x8080808080808080ul

/* Return the high bit set in the first byte that is a zero */
static inline unsigned long has_zero(unsigned long a)
{
        return ((a - ONEBYTES) & ~a) & HIGHBITS;
}

/*
 * Calculate the length and hash of the path component, and
 * return the beginning of the next one (or the pointer to the
 * final NUL character if none).
 */
static inline const char *hash_name(struct qstr *str, const char *name)
{
        unsigned long a, mask;
        unsigned long hash = 0;
        unsigned long len = 0;

        str->name = name;
        a = 0;
        len = -sizeof(unsigned long);
        do {
                hash = (hash + a) * 11;
                len += sizeof(unsigned long);
                a = *(unsigned long *)(name+len);
                /* Do we have any NUL or '/' bytes in this word? */
                mask = has_zero(a) | has_zero(a ^ SLASHBYTES);
        } while (!mask);

        /* The mask *below* the first high bit set */
        mask = (mask - 1) & ~mask;
        mask >>= 7;
        hash += a & mask;
        str->hash = fold_hash(hash);

        /* Get the final path component length */
        len += ffz(mask) / 8;
        str->len = len;

        /* remove trailing slashes */
        while (name[len] == '/')
                len++;

        return name+len;
}