[Xen-changelog] [xen-unstable] [IA64] linux/include/linux/hash.h.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User awilliam@xxxxxxxxxxx
# Node ID 435e2275ea62428ac60c27b1af585656d67ac6bb
# Parent  c8fa605f131fa9422d90f286445c909e63fd6f7a
[IA64] linux/include/linux/hash.h.

Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
---
 xen/include/asm-ia64/linux/README.origin |    1 
 xen/include/asm-ia64/linux/hash.h        |   58 +++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff -r c8fa605f131f -r 435e2275ea62 xen/include/asm-ia64/linux/README.origin
--- a/xen/include/asm-ia64/linux/README.origin  Sat Oct 14 16:34:41 2006 -0600
+++ b/xen/include/asm-ia64/linux/README.origin  Sat Oct 14 16:42:15 2006 -0600
@@ -7,6 +7,7 @@ bcd.h                   -> linux/include/linux/bcd.h
 bcd.h                  -> linux/include/linux/bcd.h
 bitmap.h               -> linux/include/linux/bitmap.h
 bitops.h               -> linux/include/linux/bitops.h
+hash.h                 -> linux/include/linux/hash.h
 initrd.h               -> linux/include/linux/initrd.h
 jiffies.h              -> linux/include/linux/jiffies.h
 kmalloc_sizes.h                -> linux/include/linux/kmalloc_sizes.h
diff -r c8fa605f131f -r 435e2275ea62 xen/include/asm-ia64/linux/hash.h
--- /dev/null   Thu Jan 01 00:00:00 1970 +0000
+++ b/xen/include/asm-ia64/linux/hash.h Sat Oct 14 16:42:15 2006 -0600
@@ -0,0 +1,58 @@
+#ifndef _LINUX_HASH_H
+#define _LINUX_HASH_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
+ *
+ * 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.
+ */
+#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)
+{
+       unsigned long hash = val;
+
+#if BITS_PER_LONG == 64
+       /*  Sigh, gcc can't optimise this alone like it does for 32 bits. */
+       unsigned long n = hash;
+       n <<= 18;
+       hash -= n;
+       n <<= 33;
+       hash -= n;
+       n <<= 3;
+       hash += n;
+       n <<= 3;
+       hash -= n;
+       n <<= 4;
+       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);
+}
+       
+static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
+{
+       return hash_long((unsigned long)ptr, bits);
+}
+#endif /* _LINUX_HASH_H */

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