mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-15 00:34:10 +08:00
468a942852
This is just the infrastructure; there are no users yet. This is modelled on CONFIG_ARCH_RANDOM; a CONFIG_ symbol declares the existence of <asm/hash.h>. That file may define its own versions of various functions, and define HAVE_* symbols (no CONFIG_ prefix!) to suppress the generic ones. Included is a self-test (in lib/test_hash.c) that verifies the basics. It is NOT in general required that the arch-specific functions compute the same thing as the generic, but if a HAVE_* symbol is defined with the value 1, then equality is tested. Signed-off-by: George Spelvin <linux@sciencehorizons.net> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Greg Ungerer <gerg@linux-m68k.org> Cc: Andreas Schwab <schwab@linux-m68k.org> Cc: Philippe De Muyter <phdm@macq.eu> Cc: linux-m68k@lists.linux-m68k.org Cc: Alistair Francis <alistai@xilinx.com> Cc: Michal Simek <michal.simek@xilinx.com> Cc: Yoshinori Sato <ysato@users.sourceforge.jp> Cc: uclinux-h8-devel@lists.sourceforge.jp
105 lines
3.0 KiB
C
105 lines
3.0 KiB
C
#ifndef _LINUX_HASH_H
|
|
#define _LINUX_HASH_H
|
|
/* Fast hashing routine for ints, longs and pointers.
|
|
(C) 2002 Nadia Yvette Chambers, IBM */
|
|
|
|
#include <asm/types.h>
|
|
#include <linux/compiler.h>
|
|
|
|
/*
|
|
* The "GOLDEN_RATIO_PRIME" is used in ifs/btrfs/brtfs_inode.h and
|
|
* fs/inode.c. It's not actually prime any more (the previous primes
|
|
* were actively bad for hashing), but the name remains.
|
|
*/
|
|
#if BITS_PER_LONG == 32
|
|
#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_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_64
|
|
#else
|
|
#error Wordsize not 32 or 64
|
|
#endif
|
|
|
|
/*
|
|
* This hash multiplies the input by a large odd number and takes the
|
|
* high bits. Since multiplication propagates changes to the most
|
|
* significant end only, it is essential that the high bits of the
|
|
* product be used for the hash value.
|
|
*
|
|
* 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. (See Knuth vol 3, section 6.4, exercise 9.)
|
|
*
|
|
* These are the negative, (1 - phi) = phi**2 = (3 - sqrt(5))/2,
|
|
* which is very slightly easier to multiply by and makes no
|
|
* difference to the hash distribution.
|
|
*/
|
|
#define GOLDEN_RATIO_32 0x61C88647
|
|
#define GOLDEN_RATIO_64 0x61C8864680B583EBull
|
|
|
|
#ifdef CONFIG_HAVE_ARCH_HASH
|
|
/* This header may use the GOLDEN_RATIO_xx constants */
|
|
#include <asm/hash.h>
|
|
#endif
|
|
|
|
/*
|
|
* The _generic versions exist only so lib/test_hash.c can compare
|
|
* the arch-optimized versions with the generic.
|
|
*
|
|
* Note that if you change these, any <asm/hash.h> that aren't updated
|
|
* to match need to have their HAVE_ARCH_* define values updated so the
|
|
* self-test will not false-positive.
|
|
*/
|
|
#ifndef HAVE_ARCH__HASH_32
|
|
#define __hash_32 __hash_32_generic
|
|
#endif
|
|
static inline u32 __hash_32_generic(u32 val)
|
|
{
|
|
return val * GOLDEN_RATIO_32;
|
|
}
|
|
|
|
#ifndef HAVE_ARCH_HASH_32
|
|
#define hash_32 hash_32_generic
|
|
#endif
|
|
static inline u32 hash_32_generic(u32 val, unsigned int bits)
|
|
{
|
|
/* High bits are more random, so use them. */
|
|
return __hash_32(val) >> (32 - bits);
|
|
}
|
|
|
|
#ifndef HAVE_ARCH_HASH_64
|
|
#define hash_64 hash_64_generic
|
|
#endif
|
|
static __always_inline u32 hash_64_generic(u64 val, unsigned int bits)
|
|
{
|
|
#if BITS_PER_LONG == 64
|
|
/* 64x64-bit multiply is efficient on all 64-bit processors */
|
|
return val * GOLDEN_RATIO_64 >> (64 - bits);
|
|
#else
|
|
/* Hash 64 bits using only 32x32-bit multiply. */
|
|
return hash_32((u32)val ^ __hash_32(val >> 32), bits);
|
|
#endif
|
|
}
|
|
|
|
static inline u32 hash_ptr(const void *ptr, unsigned int bits)
|
|
{
|
|
return hash_long((unsigned long)ptr, bits);
|
|
}
|
|
|
|
/* This really should be called fold32_ptr; it does no hashing to speak of. */
|
|
static inline u32 hash32_ptr(const void *ptr)
|
|
{
|
|
unsigned long val = (unsigned long)ptr;
|
|
|
|
#if BITS_PER_LONG == 64
|
|
val ^= (val >> 32);
|
|
#endif
|
|
return (u32)val;
|
|
}
|
|
|
|
#endif /* _LINUX_HASH_H */
|