Release 4.12 include/linux/hash.h
#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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| George Spelvin | 13 | 86.67% | 3 | 75.00% |
| Rusty Russell | 2 | 13.33% | 1 | 25.00% |
| Total | 15 | 100.00% | 4 | 100.00% |
#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);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| George Spelvin | 11 | 40.74% | 3 | 60.00% |
| Matthew Wilcox | 9 | 33.33% | 1 | 20.00% |
| Rusty Russell | 7 | 25.93% | 1 | 20.00% |
| Total | 27 | 100.00% | 5 | 100.00% |
#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
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| George Spelvin | 35 | 64.81% | 2 | 50.00% |
| Matthew Wilcox | 12 | 22.22% | 1 | 25.00% |
| Rusty Russell | 7 | 12.96% | 1 | 25.00% |
| Total | 54 | 100.00% | 4 | 100.00% |
static inline u32 hash_ptr(const void *ptr, unsigned int bits)
{
return hash_long((unsigned long)ptr, bits);
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Rusty Russell | 26 | 92.86% | 1 | 33.33% |
| George Spelvin | 1 | 3.57% | 1 | 33.33% |
| Ian Campbell | 1 | 3.57% | 1 | 33.33% |
| Total | 28 | 100.00% | 3 | 100.00% |
/* 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;
}
Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| Pavel Emelyanov | 43 | 100.00% | 1 | 100.00% |
| Total | 43 | 100.00% | 1 | 100.00% |
#endif /* _LINUX_HASH_H */
Overall Contributors
| Person | Tokens | Prop | Commits | CommitProp |
| George Spelvin | 102 | 37.23% | 3 | 30.00% |
| Rusty Russell | 73 | 26.64% | 1 | 10.00% |
| Matthew Wilcox | 43 | 15.69% | 1 | 10.00% |
| Pavel Emelyanov | 43 | 15.69% | 1 | 10.00% |
| Linus Torvalds | 8 | 2.92% | 1 | 10.00% |
| Masami Hiramatsu | 3 | 1.09% | 1 | 10.00% |
| Ian Campbell | 1 | 0.36% | 1 | 10.00% |
| Nadia Yvette Chambers | 1 | 0.36% | 1 | 10.00% |
| Total | 274 | 100.00% | 10 | 100.00% |
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