No. 0
[include/linux/hash.h]
#ifndef _LINUX_HASH_H
#define _LINUX_HASH_H
/* Fast hashing routine for ints, longs and pointers.
(C) 2002 William Lee Irwin III, 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>
/* 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 inline u64 hash_64(u64 val, unsigned int bits)
{
u64 hash = val;
/* 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;
/* 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(void *ptr, unsigned int bits)
{
return hash_long((unsigned long)ptr, bits);
}
#endif /* _LINUX_HASH_H */No. 1
[/arch/ia64/kernel/unwind.c]
static inline unw_hash_index_t
hash (unsigned long ip)
{
#define hashmagic 0x9e3779b97f4a7c16UL /* based on (sqrt(5)/2-1)*2^64 */
return (ip >> 4)*hashmagic >> (64 - UNW_LOG_HASH_SIZE);
#undef hashmagic
}
#define UNW_LOG_CACHE_SIZE 7 /* each unw_script is ~256 bytes in size */
#define UNW_CACHE_SIZE (1 << UNW_LOG_CACHE_SIZE)
#define UNW_LOG_HASH_SIZE (UNW_LOG_CACHE_SIZE + 1)
#define UNW_HASH_SIZE (1 << UNW_LOG_HASH_SIZE)
No. 2
[/fs/block_dev.c]
#define MINORBITS 20
#define MINORMASK ((1U << MINORBITS) - 1)
#define MAJOR(dev) ((unsigned int) ((dev) >> MINORBITS))
#define MINOR(dev) ((unsigned int) ((dev) & MINORMASK))
/*
* Most likely _very_ bad one - but then it's hardly critical for small
* /dev and can be fixed when somebody will need really large one.
* Keep in mind that it will be fed through icache hash function too.
*/
static inline unsigned long hash(dev_t dev)
{
return MAJOR(dev)+MINOR(dev);
}No. 3
static inline unsigned long hash(struct super_block *sb, unsigned long hashval)
{
unsigned long tmp;
tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
L1_CACHE_BYTES;
tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> I_HASHBITS);
return tmp & I_HASHMASK;
}
/*
* 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.
*/
#if BITS_PER_LONG == 32
/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
#define GOLDEN_RATIO_PRIME 0x9e370001UL
#elif BITS_PER_LONG == 64
/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
#else
#error Define GOLDEN_RATIO_PRIME for your wordsize.
#endif
/*
* Inode lookup is no longer as critical as it used to be:
* most of the lookups are going to be through the dcache.
*/
#define I_HASHBITS i_hash_shift
#define I_HASHMASK i_hash_mask
static unsigned int i_hash_mask;
static unsigned int i_hash_shift;
/* L1 cache line size */
#define L1_CACHE_SHIFT (CONFIG_X86_L1_CACHE_SHIFT)
#define L1_CACHE_BYTES (1 << L1_CACHE_SHIFT)No. 4
/* Borrowed from buffer.c: this is a tried and tested block hash function */
static inline int hash(journal_t *journal, unsigned long block)
{
struct jbd_revoke_table_s *table = journal->j_revoke;
int hash_shift = table->hash_shift;
return ((block << (hash_shift - 6)) ^
(block >> 13) ^
(block << (hash_shift - 12))) & (table->hash_size - 1);
}No. 5
[/fs/namespace.c]
static int hash_mask, hash_bits;
static kmem_cache_t *mnt_cache;
static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
unsigned long tmp = ((unsigned long) mnt / L1_CACHE_BYTES);
tmp += ((unsigned long) dentry / L1_CACHE_BYTES);
tmp = tmp + (tmp >> hash_bits);
return tmp & hash_mask;
}No. 6
[/init/initramfs.c]
static inline int hash(int major, int minor, int ino)
{
unsigned long tmp = ino + minor + (major << 3);
tmp += tmp >> 5;
return tmp & 31;
}No. 7
[/net/tipc/name_table.c]
static int tipc_nametbl_size = 1024; /* must be a power of 2 */
static int hash(int x)
{
return x & (tipc_nametbl_size - 1);
}