X-Git-Url: https://git.kernel.dk/?p=fio.git;a=blobdiff_plain;f=hash.h;h=51f0706e2cc5cc5a310efaf43b86b3417ef8d198;hp=13600f4e5e4b3602df1e59636e3d687b1ce0dc82;hb=9dc528b1638b625b5e167983a74de4e85c5859ea;hpb=a5a4fdfd44ec1b55ebab7800a931c148540a7324

diff --git a/hash.h b/hash.h
index 13600f4e..51f0706e 100644
--- a/hash.h
+++ b/hash.h
@@ -3,40 +3,31 @@
 
 #include <inttypes.h>
 #include "arch/arch.h"
+#include "compiler/compiler.h"
 
 /* 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
+ * 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.
  *
- * 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.
+ * These are the negative, (1 - phi) = (phi^2) = (3 - sqrt(5))/2.
+ * (See Knuth vol 3, section 6.4, exercise 9.)
  */
+#define GOLDEN_RATIO_32 0x61C88647
+#define GOLDEN_RATIO_64 0x61C8864680B583EBull
 
-#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
-
-#define GR_PRIME_64	0x9e37fffffffc0001UL
-
-static inline unsigned long __hash_long(unsigned long val)
+static inline unsigned long __hash_long(uint64_t val)
 {
-	unsigned long hash = val;
+	uint64_t hash = val;
 
 #if BITS_PER_LONG == 64
+	hash *= GOLDEN_RATIO_64;
+#else
 	/*  Sigh, gcc can't optimise this alone like it does for 32 bits. */
-	unsigned long n = hash;
+	uint64_t n = hash;
 	n <<= 18;
 	hash -= n;
 	n <<= 33;
@@ -49,9 +40,6 @@ static inline unsigned long __hash_long(unsigned long val)
 	hash += n;
 	n <<= 2;
 	hash += n;
-#else
-	/* On some cpus multiply is faster, on others gcc will do shifts */
-	hash *= GOLDEN_RATIO_PRIME;
 #endif
 
 	return hash;
@@ -65,7 +53,7 @@ static inline unsigned long hash_long(unsigned long val, unsigned int bits)
 
 static inline uint64_t __hash_u64(uint64_t val)
 {
-	return val * GR_PRIME_64;
+	return val * GOLDEN_RATIO_64;
 }
 	
 static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
@@ -77,7 +65,7 @@ static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
  * Bob Jenkins jhash
  */
 
-#define JHASH_INITVAL	GOLDEN_RATIO_PRIME
+#define JHASH_INITVAL	GOLDEN_RATIO_32
 
 static inline uint32_t rol32(uint32_t word, uint32_t shift)
 {
@@ -128,19 +116,20 @@ static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
 	/* Last block: affect all 32 bits of (c) */
 	/* All the case statements fall through */
 	switch (length) {
-	case 12: c += (uint32_t) k[11] << 24;
-	case 11: c += (uint32_t) k[10] << 16;
-	case 10: c += (uint32_t) k[9] << 8;
-	case 9:  c += k[8];
-	case 8:  b += (uint32_t) k[7] << 24;
-	case 7:  b += (uint32_t) k[6] << 16;
-	case 6:  b += (uint32_t) k[5] << 8;
-	case 5:  b += k[4];
-	case 4:  a += (uint32_t) k[3] << 24;
-	case 3:  a += (uint32_t) k[2] << 16;
-	case 2:  a += (uint32_t) k[1] << 8;
+	case 12: c += (uint32_t) k[11] << 24;	fio_fallthrough;
+	case 11: c += (uint32_t) k[10] << 16;	fio_fallthrough;
+	case 10: c += (uint32_t) k[9] << 8;	fio_fallthrough;
+	case 9:  c += k[8];			fio_fallthrough;
+	case 8:  b += (uint32_t) k[7] << 24;	fio_fallthrough;
+	case 7:  b += (uint32_t) k[6] << 16;	fio_fallthrough;
+	case 6:  b += (uint32_t) k[5] << 8;	fio_fallthrough;
+	case 5:  b += k[4];			fio_fallthrough;
+	case 4:  a += (uint32_t) k[3] << 24;	fio_fallthrough;
+	case 3:  a += (uint32_t) k[2] << 16;	fio_fallthrough;
+	case 2:  a += (uint32_t) k[1] << 8;	fio_fallthrough;
 	case 1:  a += k[0];
 		 __jhash_final(a, b, c);
+		 fio_fallthrough;
 	case 0: /* Nothing left to add */
 		break;
 	}