X-Git-Url: https://git.kernel.dk/?p=fio.git;a=blobdiff_plain;f=hash.h;h=d227b938a246881229ab5d5e304427da8f03cff3;hp=73f961b73ac77975bd7a86eb8c7b49d995e05408;hb=e97412c38bedc4f365bdf4abe1ff8f6694587a86;hpb=daaa166fb4d4869882885094d8b8ad44f6d159ce

diff --git a/hash.h b/hash.h
index 73f961b7..d227b938 100644
--- a/hash.h
+++ b/hash.h
@@ -1,6 +1,7 @@
 #ifndef _LINUX_HASH_H
 #define _LINUX_HASH_H
 
+#include <inttypes.h>
 #include "arch/arch.h"
 
 /* Fast hashing routine for a long.
@@ -27,13 +28,31 @@
 #error Define GOLDEN_RATIO_PRIME for your wordsize.
 #endif
 
-static inline unsigned long hash_long(unsigned long val, unsigned int bits)
+/*
+ * 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.
+ *
+ * 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
+
+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;
@@ -46,17 +65,100 @@ static inline unsigned long hash_long(unsigned long val, unsigned int bits)
 	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;
+	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 1:  a += k[0];
+		 __jhash_final(a, b, c);
+	case 0: /* Nothing left to add */
+		break;
+	}
+
+	return c;
+}
+
 #endif /* _LINUX_HASH_H */