hash: cleanups

- Use __hash_u64() for __fill_random_buffer()
- Convert rdma to use GOLDEN_RATIO_64

That's the last user of GOLDEN_RATIO_PRIME, which due to bit sparseness
isn't really useful for our purposes.

Signed-off-by: Jens Axboe <[email protected]>

Author: axboe

engines/rdma.c

@@ -1389,7 +1389,7 @@ static int fio_rdmaio_setup(struct thread_data *td)
 		rd = malloc(sizeof(*rd));
 
 		memset(rd, 0, sizeof(*rd));
-		init_rand_seed(&rd->rand_state, (unsigned int) GOLDEN_RATIO_PRIME, 0);
+		init_rand_seed(&rd->rand_state, (unsigned int) GOLDEN_RATIO_64, 0);
 		td->io_ops_data = rd;
 	}
 

hash.h

@@ -9,32 +9,6 @@
    (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
-
-/*
- * The above primes are actively bad for hashing, since they are
- * too sparse. The 32-bit one is mostly ok, the 64-bit one causes
- * real problems. Besides, the "prime" part is pointless for the
- * multiplicative hash.
- *
  * Although a random odd number will do, it turns out that the golden
  * ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
  * properties.

lib/rand.c

@@ -103,7 +103,7 @@ void __fill_random_buf(void *buf, unsigned int len, uint64_t seed)
 
 	for (; b != e; ++b) {
 		*b = seed;
-		seed *= GOLDEN_RATIO_64;
+		seed = __hash_u64(seed);
 	}
 
 	if (fio_unlikely(rest))