hash: add explicit u32 and u64 versions of hash
The 32-bit version is more efficient (and apparently gives better hash
results than the 64-bit version), so users who are only hashing a 32-bit
quantity can now opt to use the 32-bit version explicitly, rather than
promoting to a long.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: William Lee Irwin III <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/hash.h b/include/linux/hash.h
index acf17bb..06d25c1 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -1,6 +1,6 @@
#ifndef _LINUX_HASH_H
#define _LINUX_HASH_H
-/* Fast hashing routine for a long.
+/* Fast hashing routine for ints, longs and pointers.
(C) 2002 William Lee Irwin III, IBM */
/*
@@ -13,23 +13,30 @@
* them can use shifts and additions instead of multiplications for
* machines where multiplications are slow.
*/
-#if BITS_PER_LONG == 32
+
+#include <asm/types.h>
+
/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
-#define GOLDEN_RATIO_PRIME 0x9e370001UL
-#elif BITS_PER_LONG == 64
+#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
-#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
+#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL
+
+#if BITS_PER_LONG == 32
+#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_32
+#define hash_long(val, bits) hash_32(val, bits)
+#elif BITS_PER_LONG == 64
+#define hash_long(val, bits) hash_64(val, bits)
+#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_64
#else
-#error Define GOLDEN_RATIO_PRIME for your wordsize.
+#error Wordsize not 32 or 64
#endif
-static inline unsigned long hash_long(unsigned long val, unsigned int bits)
+static inline u64 hash_64(u64 val, unsigned int bits)
{
- unsigned long hash = val;
+ u64 hash = val;
-#if BITS_PER_LONG == 64
/* Sigh, gcc can't optimise this alone like it does for 32 bits. */
- unsigned long n = hash;
+ u64 n = hash;
n <<= 18;
hash -= n;
n <<= 33;
@@ -42,15 +49,20 @@
hash += n;
n <<= 2;
hash += n;
-#else
- /* On some cpus multiply is faster, on others gcc will do shifts */
- hash *= GOLDEN_RATIO_PRIME;
-#endif
/* High bits are more random, so use them. */
- return hash >> (BITS_PER_LONG - bits);
+ return hash >> (64 - bits);
}
-
+
+static inline u32 hash_32(u32 val, unsigned int bits)
+{
+ /* On some cpus multiply is faster, on others gcc will do shifts */
+ u32 hash = val * GOLDEN_RATIO_PRIME_32;
+
+ /* High bits are more random, so use them. */
+ return hash >> (32 - bits);
+}
+
static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
{
return hash_long((unsigned long)ptr, bits);