cregit-Linux how code gets into the kernel

Release 4.12 include/linux/hash.h

Directory: include/linux
#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

PersonTokensPropCommitsCommitProp
George Spelvin1386.67%375.00%
Rusty Russell213.33%125.00%
Total15100.00%4100.00%

#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

PersonTokensPropCommitsCommitProp
George Spelvin1140.74%360.00%
Matthew Wilcox933.33%120.00%
Rusty Russell725.93%120.00%
Total27100.00%5100.00%

#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

PersonTokensPropCommitsCommitProp
George Spelvin3564.81%250.00%
Matthew Wilcox1222.22%125.00%
Rusty Russell712.96%125.00%
Total54100.00%4100.00%


static inline u32 hash_ptr(const void *ptr, unsigned int bits) { return hash_long((unsigned long)ptr, bits); }

Contributors

PersonTokensPropCommitsCommitProp
Rusty Russell2692.86%133.33%
George Spelvin13.57%133.33%
Ian Campbell13.57%133.33%
Total28100.00%3100.00%

/* 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

PersonTokensPropCommitsCommitProp
Pavel Emelyanov43100.00%1100.00%
Total43100.00%1100.00%

#endif /* _LINUX_HASH_H */

Overall Contributors

PersonTokensPropCommitsCommitProp
George Spelvin10237.23%330.00%
Rusty Russell7326.64%110.00%
Matthew Wilcox4315.69%110.00%
Pavel Emelyanov4315.69%110.00%
Linus Torvalds82.92%110.00%
Masami Hiramatsu31.09%110.00%
Ian Campbell10.36%110.00%
Nadia Yvette Chambers10.36%110.00%
Total274100.00%10100.00%
Directory: include/linux
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