mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-10-27 22:51:31 +00:00
a77f9c5dcd
This reverts commite5a2c89995. Commite5a2c899introduced an alternative_call, arch_fast_hash2, that selects between __jhash2 and __intel_crc4_2_hash based on the X86_FEATURE_XMM4_2. Unfortunately, the alternative_call system does not appear to be suitable for use with C functions, as register usage is not handled properly for the called functions. The __jhash2 function in particular clobbers registers that are not preserved when called via alternative_call, resulting in a panic for direct callers of arch_fast_hash2 on older CPUs lacking sse4_2. It is possible that __intel_crc4_2_hash works merely by chance because it uses fewer registers. This commit was suggested as the source of the problem by Jesse Gross <jesse@nicira.com>. Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com> Signed-off-by: David S. Miller <davem@davemloft.net>
121 lines
3.2 KiB
C
121 lines
3.2 KiB
C
#ifndef _LINUX_HASH_H
|
|
#define _LINUX_HASH_H
|
|
/* Fast hashing routine for ints, longs and pointers.
|
|
(C) 2002 Nadia Yvette Chambers, 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.
|
|
*/
|
|
|
|
#include <asm/types.h>
|
|
#include <asm/hash.h>
|
|
#include <linux/compiler.h>
|
|
|
|
/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
|
|
#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
|
|
/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
|
|
#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL
|
|
|
|
#if BITS_PER_LONG == 32
|
|
#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_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_PRIME_64
|
|
#else
|
|
#error Wordsize not 32 or 64
|
|
#endif
|
|
|
|
static __always_inline u64 hash_64(u64 val, unsigned int bits)
|
|
{
|
|
u64 hash = val;
|
|
|
|
#if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
|
|
hash = hash * GOLDEN_RATIO_PRIME_64;
|
|
#else
|
|
/* Sigh, gcc can't optimise this alone like it does for 32 bits. */
|
|
u64 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;
|
|
#endif
|
|
|
|
/* High bits are more random, so use them. */
|
|
return hash >> (64 - bits);
|
|
}
|
|
|
|
static inline u32 hash_32(u32 val, unsigned int bits)
|
|
{
|
|
/* On some cpus multiply is faster, on others gcc will do shifts */
|
|
u32 hash = val * GOLDEN_RATIO_PRIME_32;
|
|
|
|
/* High bits are more random, so use them. */
|
|
return hash >> (32 - bits);
|
|
}
|
|
|
|
static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
|
|
{
|
|
return hash_long((unsigned long)ptr, bits);
|
|
}
|
|
|
|
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;
|
|
}
|
|
|
|
struct fast_hash_ops {
|
|
u32 (*hash)(const void *data, u32 len, u32 seed);
|
|
u32 (*hash2)(const u32 *data, u32 len, u32 seed);
|
|
};
|
|
|
|
/**
|
|
* arch_fast_hash - Caclulates a hash over a given buffer that can have
|
|
* arbitrary size. This function will eventually use an
|
|
* architecture-optimized hashing implementation if
|
|
* available, and trades off distribution for speed.
|
|
*
|
|
* @data: buffer to hash
|
|
* @len: length of buffer in bytes
|
|
* @seed: start seed
|
|
*
|
|
* Returns 32bit hash.
|
|
*/
|
|
extern u32 arch_fast_hash(const void *data, u32 len, u32 seed);
|
|
|
|
/**
|
|
* arch_fast_hash2 - Caclulates a hash over a given buffer that has a
|
|
* size that is of a multiple of 32bit words. This
|
|
* function will eventually use an architecture-
|
|
* optimized hashing implementation if available,
|
|
* and trades off distribution for speed.
|
|
*
|
|
* @data: buffer to hash (must be 32bit padded)
|
|
* @len: number of 32bit words
|
|
* @seed: start seed
|
|
*
|
|
* Returns 32bit hash.
|
|
*/
|
|
extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed);
|
|
|
|
#endif /* _LINUX_HASH_H */
|