cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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hash.h (2998B)

      1#ifndef _LINUX_HASH_H
      2#define _LINUX_HASH_H
      3/* Fast hashing routine for ints,  longs and pointers.
      4   (C) 2002 Nadia Yvette Chambers, IBM */
      5
      6#include <asm/types.h>
      7#include <linux/compiler.h>
      8
      9/*
     10 * The "GOLDEN_RATIO_PRIME" is used in ifs/btrfs/brtfs_inode.h and
     11 * fs/inode.c.  It's not actually prime any more (the previous primes
     12 * were actively bad for hashing), but the name remains.
     13 */
     14#if BITS_PER_LONG == 32
     15#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_32
     16#define hash_long(val, bits) hash_32(val, bits)
     17#elif BITS_PER_LONG == 64
     18#define hash_long(val, bits) hash_64(val, bits)
     19#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_64
     20#else
     21#error Wordsize not 32 or 64
     22#endif
     23
     24/*
     25 * This hash multiplies the input by a large odd number and takes the
     26 * high bits.  Since multiplication propagates changes to the most
     27 * significant end only, it is essential that the high bits of the
     28 * product be used for the hash value.
     29 *
     30 * Chuck Lever verified the effectiveness of this technique:
     31 * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
     32 *
     33 * Although a random odd number will do, it turns out that the golden
     34 * ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
     35 * properties.  (See Knuth vol 3, section 6.4, exercise 9.)
     36 *
     37 * These are the negative, (1 - phi) = phi**2 = (3 - sqrt(5))/2,
     38 * which is very slightly easier to multiply by and makes no
     39 * difference to the hash distribution.
     40 */
     41#define GOLDEN_RATIO_32 0x61C88647
     42#define GOLDEN_RATIO_64 0x61C8864680B583EBull
     43
     44#ifdef CONFIG_HAVE_ARCH_HASH
     45/* This header may use the GOLDEN_RATIO_xx constants */
     46#include <asm/hash.h>
     47#endif
     48
     49/*
     50 * The _generic versions exist only so lib/test_hash.c can compare
     51 * the arch-optimized versions with the generic.
     52 *
     53 * Note that if you change these, any <asm/hash.h> that aren't updated
     54 * to match need to have their HAVE_ARCH_* define values updated so the
     55 * self-test will not false-positive.
     56 */
     57#ifndef HAVE_ARCH__HASH_32
     58#define __hash_32 __hash_32_generic
     59#endif
     60static inline u32 __hash_32_generic(u32 val)
     61{
     62	return val * GOLDEN_RATIO_32;
     63}
     64
     65static inline u32 hash_32(u32 val, unsigned int bits)
     66{
     67	/* High bits are more random, so use them. */
     68	return __hash_32(val) >> (32 - bits);
     69}
     70
     71#ifndef HAVE_ARCH_HASH_64
     72#define hash_64 hash_64_generic
     73#endif
     74static __always_inline u32 hash_64_generic(u64 val, unsigned int bits)
     75{
     76#if BITS_PER_LONG == 64
     77	/* 64x64-bit multiply is efficient on all 64-bit processors */
     78	return val * GOLDEN_RATIO_64 >> (64 - bits);
     79#else
     80	/* Hash 64 bits using only 32x32-bit multiply. */
     81	return hash_32((u32)val ^ __hash_32(val >> 32), bits);
     82#endif
     83}
     84
     85static inline u32 hash_ptr(const void *ptr, unsigned int bits)
     86{
     87	return hash_long((unsigned long)ptr, bits);
     88}
     89
     90/* This really should be called fold32_ptr; it does no hashing to speak of. */
     91static inline u32 hash32_ptr(const void *ptr)
     92{
     93	unsigned long val = (unsigned long)ptr;
     94
     95#if BITS_PER_LONG == 64
     96	val ^= (val >> 32);
     97#endif
     98	return (u32)val;
     99}
    100
    101#endif /* _LINUX_HASH_H */