/* Fast hashing routine for a long.
   (C) 2002 William Lee Irwin III, IBM */

/*
 * Knuth recommends primes in approximately golden ratio to the maximum
 * integer representable by a machine word for multiplicative hashing.
 * Chuck Lever verified the effectiveness of this technique:
 * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
 *
 * These primes are chosen to be bit-sparse, that is operations on
 * them can use shifts and additions instead of multiplications for
 * machines where multiplications are slow.
 */
#if BITS_PER_LONG == 32
/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
#define GOLDEN_RATIO_PRIME 0x9e370001UL
#elif BITS_PER_LONG == 64
/*  2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
#else
#error Define GOLDEN_RATIO_PRIME for your wordsize.
#endif

static inline unsigned long hash_long(unsigned long val, unsigned int bits)
{
	unsigned long hash = val;

#if BITS_PER_LONG == 64
	/*  Sigh, gcc can't optimise this alone like it does for 32 bits. */
	unsigned long n = hash;
	n <<= 18;
	hash -= n;
	n <<= 33;
	hash -= n;
	n <<= 3;
	hash += n;
	n <<= 3;
	hash -= n;
	n <<= 4;
	hash += n;
	n <<= 2;
	hash += n;
#else
	/* On some cpus multiply is faster, on others gcc will do shifts */
	hash *= GOLDEN_RATIO_PRIME;
#endif

	/* High bits are more random, so use them. */
	return hash >> (BITS_PER_LONG - bits);
}
	
static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
{
	return hash_long((unsigned long)ptr, bits);
}

static inline unsigned long hash_str(char *name, int bits)
{
	unsigned long hash = 0;
	unsigned long l = 0;
	int len = 0;
	unsigned char c;
	do {
		if (!(c = *name++)) {
			c = (char)len; len = -1;
		}
		l = (l << 8) | c;
		len++;
		if ((len & (BITS_PER_LONG/8-1))==0)
			hash = hash_long(hash^l, BITS_PER_LONG);
	} while (len);
	return hash >> (BITS_PER_LONG - bits);
}

static inline unsigned long hash_mem(char *buf, int length, int bits)
{
	unsigned long hash = 0;
	unsigned long l = 0;
	int len = 0;
	unsigned char c;
	do {
		if (len == length) {
			c = (char)len; len = -1;
		} else
			c = *buf++;
		l = (l << 8) | c;
		len++;
		if ((len & (BITS_PER_LONG/8-1))==0)
			hash = hash_long(hash^l, BITS_PER_LONG);
	} while (len);
	return hash >> (BITS_PER_LONG - bits);
}
