#ifndef _LINUX_HASH_H
#define _LINUX_HASH_H
+
+#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
-#ifdef __WORDSIZE
-#define BITS_PER_LONG __WORDSIZE
-#else
-#define BITS_PER_LONG 32
-#endif
-
-#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)
+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;
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;
+}
+
+static inline unsigned long hash_long(unsigned long val, unsigned int bits)
+{
/* High bits are more random, so use them. */
- return hash >> (BITS_PER_LONG - bits);
+ return __hash_long(val) >> (BITS_PER_LONG - bits);
+}
+
+static inline uint64_t __hash_u64(uint64_t val)
+{
+ return val * GOLDEN_RATIO_64;
}
static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
{
- return hash_long((unsigned long)ptr, bits);
+ return hash_long((uintptr_t)ptr, bits);
}
+
+/*
+ * Bob Jenkins jhash
+ */
+
+#define JHASH_INITVAL GOLDEN_RATIO_32
+
+static inline uint32_t rol32(uint32_t word, uint32_t shift)
+{
+ return (word << shift) | (word >> (32 - shift));
+}
+
+/* __jhash_mix -- mix 3 32-bit values reversibly. */
+#define __jhash_mix(a, b, c) \
+{ \
+ a -= c; a ^= rol32(c, 4); c += b; \
+ b -= a; b ^= rol32(a, 6); a += c; \
+ c -= b; c ^= rol32(b, 8); b += a; \
+ a -= c; a ^= rol32(c, 16); c += b; \
+ b -= a; b ^= rol32(a, 19); a += c; \
+ c -= b; c ^= rol32(b, 4); b += a; \
+}
+
+/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */
+#define __jhash_final(a, b, c) \
+{ \
+ c ^= b; c -= rol32(b, 14); \
+ a ^= c; a -= rol32(c, 11); \
+ b ^= a; b -= rol32(a, 25); \
+ c ^= b; c -= rol32(b, 16); \
+ a ^= c; a -= rol32(c, 4); \
+ b ^= a; b -= rol32(a, 14); \
+ c ^= b; c -= rol32(b, 24); \
+}
+
+static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval)
+{
+ const uint8_t *k = key;
+ uint32_t a, b, c;
+
+ /* Set up the internal state */
+ a = b = c = JHASH_INITVAL + length + initval;
+
+ /* All but the last block: affect some 32 bits of (a,b,c) */
+ while (length > 12) {
+ a += *k;
+ b += *(k + 4);
+ c += *(k + 8);
+ __jhash_mix(a, b, c);
+ length -= 12;
+ k += 12;
+ }
+
+ /* Last block: affect all 32 bits of (c) */
+ /* All the case statements fall through */
+ switch (length) {
+ 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;
+ }
+
+ return c;
+}
+
#endif /* _LINUX_HASH_H */
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