From dadf66c5240716a61f3861c29bebf97f29b1ea96 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 6 Oct 2011 12:37:10 +0200
Subject: [PATCH] Add jhash (Jenkins hash) and use that for file names

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 filehash.c |  4 +--
 hash.h     | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 79 insertions(+), 2 deletions(-)

diff --git a/filehash.c b/filehash.c
index 1df7db0c..1bb1eb23 100644
--- a/filehash.c
+++ b/filehash.c
@@ -3,7 +3,7 @@
 
 #include "fio.h"
 #include "flist.h"
-#include "crc/crc16.h"
+#include "hash.h"
 
 #define HASH_BUCKETS	512
 #define HASH_MASK	(HASH_BUCKETS - 1)
@@ -15,7 +15,7 @@ static struct fio_mutex *hash_lock;
 
 static unsigned short hash(const char *name)
 {
-	return crc16((const unsigned char *) name, strlen(name)) & HASH_MASK;
+	return jhash(name, strlen(name), 0) & HASH_MASK;
 }
 
 void remove_file_hash(struct fio_file *f)
diff --git a/hash.h b/hash.h
index 73f961b7..0c3cdda7 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.
@@ -59,4 +60,80 @@ static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
 {
 	return hash_long((unsigned long)ptr, bits);
 }
+
+/*
+ * Bob Jenkins jhash
+ */
+
+#define JHASH_INITVAL	GOLDEN_RATIO_PRIME
+
+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 */
-- 
2.25.1