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b8b2e3b2de
The latter was already the dominant use, and it's preferable because in C the convention is that intXX means XX bits. Therefore, allowing mixed use of int2, int4, int8, int16, int32 is obviously confusing. Remove the typedefs for int2 and int4 for now. They don't seem to be widely used outside of the PostgreSQL source tree, and the few uses can probably be cleaned up by the time this ships.
524 lines
14 KiB
C
524 lines
14 KiB
C
/*-------------------------------------------------------------------------
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*
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* hashfunc.c
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* Support functions for hash access method.
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*
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* Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/access/hash/hashfunc.c
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*
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* NOTES
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* These functions are stored in pg_amproc. For each operator class
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* defined for hash indexes, they compute the hash value of the argument.
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*
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* Additional hash functions appear in /utils/adt/ files for various
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* specialized datatypes.
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*
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* It is expected that every bit of a hash function's 32-bit result is
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* as random as every other; failure to ensure this is likely to lead
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* to poor performance of hash joins, for example. In most cases a hash
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* function should use hash_any() or its variant hash_uint32().
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/hash.h"
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/* Note: this is used for both "char" and boolean datatypes */
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Datum
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hashchar(PG_FUNCTION_ARGS)
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{
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return hash_uint32((int32) PG_GETARG_CHAR(0));
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}
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Datum
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hashint2(PG_FUNCTION_ARGS)
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{
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return hash_uint32((int32) PG_GETARG_INT16(0));
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}
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Datum
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hashint4(PG_FUNCTION_ARGS)
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{
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return hash_uint32(PG_GETARG_INT32(0));
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}
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Datum
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hashint8(PG_FUNCTION_ARGS)
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{
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/*
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* The idea here is to produce a hash value compatible with the values
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* produced by hashint4 and hashint2 for logically equal inputs; this is
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* necessary to support cross-type hash joins across these input types.
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* Since all three types are signed, we can xor the high half of the int8
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* value if the sign is positive, or the complement of the high half when
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* the sign is negative.
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*/
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int64 val = PG_GETARG_INT64(0);
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uint32 lohalf = (uint32) val;
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uint32 hihalf = (uint32) (val >> 32);
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lohalf ^= (val >= 0) ? hihalf : ~hihalf;
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return hash_uint32(lohalf);
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}
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Datum
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hashoid(PG_FUNCTION_ARGS)
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{
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return hash_uint32((uint32) PG_GETARG_OID(0));
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}
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Datum
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hashenum(PG_FUNCTION_ARGS)
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{
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return hash_uint32((uint32) PG_GETARG_OID(0));
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}
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Datum
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hashfloat4(PG_FUNCTION_ARGS)
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{
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float4 key = PG_GETARG_FLOAT4(0);
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float8 key8;
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/*
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* On IEEE-float machines, minus zero and zero have different bit patterns
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* but should compare as equal. We must ensure that they have the same
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* hash value, which is most reliably done this way:
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*/
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if (key == (float4) 0)
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PG_RETURN_UINT32(0);
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/*
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* To support cross-type hashing of float8 and float4, we want to return
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* the same hash value hashfloat8 would produce for an equal float8 value.
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* So, widen the value to float8 and hash that. (We must do this rather
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* than have hashfloat8 try to narrow its value to float4; that could fail
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* on overflow.)
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*/
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key8 = key;
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return hash_any((unsigned char *) &key8, sizeof(key8));
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}
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Datum
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hashfloat8(PG_FUNCTION_ARGS)
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{
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float8 key = PG_GETARG_FLOAT8(0);
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/*
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* On IEEE-float machines, minus zero and zero have different bit patterns
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* but should compare as equal. We must ensure that they have the same
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* hash value, which is most reliably done this way:
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*/
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if (key == (float8) 0)
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PG_RETURN_UINT32(0);
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return hash_any((unsigned char *) &key, sizeof(key));
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}
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Datum
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hashoidvector(PG_FUNCTION_ARGS)
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{
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oidvector *key = (oidvector *) PG_GETARG_POINTER(0);
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return hash_any((unsigned char *) key->values, key->dim1 * sizeof(Oid));
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}
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Datum
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hashint2vector(PG_FUNCTION_ARGS)
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{
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int2vector *key = (int2vector *) PG_GETARG_POINTER(0);
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return hash_any((unsigned char *) key->values, key->dim1 * sizeof(int16));
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}
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Datum
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hashname(PG_FUNCTION_ARGS)
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{
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char *key = NameStr(*PG_GETARG_NAME(0));
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int keylen = strlen(key);
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Assert(keylen < NAMEDATALEN); /* else it's not truncated correctly */
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return hash_any((unsigned char *) key, keylen);
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}
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Datum
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hashtext(PG_FUNCTION_ARGS)
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{
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text *key = PG_GETARG_TEXT_PP(0);
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Datum result;
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/*
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* Note: this is currently identical in behavior to hashvarlena, but keep
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* it as a separate function in case we someday want to do something
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* different in non-C locales. (See also hashbpchar, if so.)
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*/
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result = hash_any((unsigned char *) VARDATA_ANY(key),
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VARSIZE_ANY_EXHDR(key));
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/* Avoid leaking memory for toasted inputs */
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PG_FREE_IF_COPY(key, 0);
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return result;
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}
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/*
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* hashvarlena() can be used for any varlena datatype in which there are
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* no non-significant bits, ie, distinct bitpatterns never compare as equal.
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*/
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Datum
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hashvarlena(PG_FUNCTION_ARGS)
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{
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struct varlena *key = PG_GETARG_VARLENA_PP(0);
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Datum result;
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result = hash_any((unsigned char *) VARDATA_ANY(key),
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VARSIZE_ANY_EXHDR(key));
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/* Avoid leaking memory for toasted inputs */
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PG_FREE_IF_COPY(key, 0);
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return result;
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}
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/*
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* This hash function was written by Bob Jenkins
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* (bob_jenkins@burtleburtle.net), and superficially adapted
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* for PostgreSQL by Neil Conway. For more information on this
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* hash function, see http://burtleburtle.net/bob/hash/doobs.html,
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* or Bob's article in Dr. Dobb's Journal, Sept. 1997.
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*
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* In the current code, we have adopted Bob's 2006 update of his hash
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* function to fetch the data a word at a time when it is suitably aligned.
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* This makes for a useful speedup, at the cost of having to maintain
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* four code paths (aligned vs unaligned, and little-endian vs big-endian).
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* It also uses two separate mixing functions mix() and final(), instead
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* of a slower multi-purpose function.
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*/
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/* Get a bit mask of the bits set in non-uint32 aligned addresses */
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#define UINT32_ALIGN_MASK (sizeof(uint32) - 1)
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/* Rotate a uint32 value left by k bits - note multiple evaluation! */
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#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
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/*----------
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* mix -- mix 3 32-bit values reversibly.
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*
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* This is reversible, so any information in (a,b,c) before mix() is
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* still in (a,b,c) after mix().
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*
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* If four pairs of (a,b,c) inputs are run through mix(), or through
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* mix() in reverse, there are at least 32 bits of the output that
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* are sometimes the same for one pair and different for another pair.
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* This was tested for:
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* * pairs that differed by one bit, by two bits, in any combination
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* of top bits of (a,b,c), or in any combination of bottom bits of
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* (a,b,c).
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* * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
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* the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
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* is commonly produced by subtraction) look like a single 1-bit
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* difference.
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* * the base values were pseudorandom, all zero but one bit set, or
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* all zero plus a counter that starts at zero.
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*
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* This does not achieve avalanche. There are input bits of (a,b,c)
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* that fail to affect some output bits of (a,b,c), especially of a. The
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* most thoroughly mixed value is c, but it doesn't really even achieve
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* avalanche in c.
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*
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* This allows some parallelism. Read-after-writes are good at doubling
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* the number of bits affected, so the goal of mixing pulls in the opposite
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* direction from the goal of parallelism. I did what I could. Rotates
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* seem to cost as much as shifts on every machine I could lay my hands on,
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* and rotates are much kinder to the top and bottom bits, so I used rotates.
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*----------
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*/
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#define mix(a,b,c) \
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{ \
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a -= c; a ^= rot(c, 4); c += b; \
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b -= a; b ^= rot(a, 6); a += c; \
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c -= b; c ^= rot(b, 8); b += a; \
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a -= c; a ^= rot(c,16); c += b; \
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b -= a; b ^= rot(a,19); a += c; \
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c -= b; c ^= rot(b, 4); b += a; \
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}
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/*----------
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* final -- final mixing of 3 32-bit values (a,b,c) into c
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*
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* Pairs of (a,b,c) values differing in only a few bits will usually
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* produce values of c that look totally different. This was tested for
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* * pairs that differed by one bit, by two bits, in any combination
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* of top bits of (a,b,c), or in any combination of bottom bits of
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* (a,b,c).
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* * "differ" is defined as +, -, ^, or ~^. For + and -, I transformed
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* the output delta to a Gray code (a^(a>>1)) so a string of 1's (as
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* is commonly produced by subtraction) look like a single 1-bit
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* difference.
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* * the base values were pseudorandom, all zero but one bit set, or
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* all zero plus a counter that starts at zero.
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*
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* The use of separate functions for mix() and final() allow for a
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* substantial performance increase since final() does not need to
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* do well in reverse, but is does need to affect all output bits.
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* mix(), on the other hand, does not need to affect all output
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* bits (affecting 32 bits is enough). The original hash function had
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* a single mixing operation that had to satisfy both sets of requirements
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* and was slower as a result.
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*----------
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*/
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#define final(a,b,c) \
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{ \
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c ^= b; c -= rot(b,14); \
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a ^= c; a -= rot(c,11); \
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b ^= a; b -= rot(a,25); \
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c ^= b; c -= rot(b,16); \
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a ^= c; a -= rot(c, 4); \
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b ^= a; b -= rot(a,14); \
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c ^= b; c -= rot(b,24); \
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}
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/*
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* hash_any() -- hash a variable-length key into a 32-bit value
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* k : the key (the unaligned variable-length array of bytes)
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* len : the length of the key, counting by bytes
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*
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* Returns a uint32 value. Every bit of the key affects every bit of
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* the return value. Every 1-bit and 2-bit delta achieves avalanche.
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* About 6*len+35 instructions. The best hash table sizes are powers
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* of 2. There is no need to do mod a prime (mod is sooo slow!).
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* If you need less than 32 bits, use a bitmask.
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*
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* Note: we could easily change this function to return a 64-bit hash value
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* by using the final values of both b and c. b is perhaps a little less
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* well mixed than c, however.
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*/
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Datum
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hash_any(register const unsigned char *k, register int keylen)
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{
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register uint32 a,
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b,
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c,
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len;
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/* Set up the internal state */
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len = keylen;
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a = b = c = 0x9e3779b9 + len + 3923095;
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/* If the source pointer is word-aligned, we use word-wide fetches */
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if (((intptr_t) k & UINT32_ALIGN_MASK) == 0)
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{
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/* Code path for aligned source data */
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register const uint32 *ka = (const uint32 *) k;
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/* handle most of the key */
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while (len >= 12)
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{
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a += ka[0];
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b += ka[1];
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c += ka[2];
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mix(a, b, c);
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ka += 3;
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len -= 12;
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}
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/* handle the last 11 bytes */
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k = (const unsigned char *) ka;
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#ifdef WORDS_BIGENDIAN
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 8);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 24);
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/* the lowest byte of c is reserved for the length */
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/* fall through */
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case 8:
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b += ka[1];
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a += ka[0];
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break;
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case 7:
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b += ((uint32) k[6] << 8);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 16);
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/* fall through */
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case 5:
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b += ((uint32) k[4] << 24);
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/* fall through */
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case 4:
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a += ka[0];
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break;
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case 3:
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a += ((uint32) k[2] << 8);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 16);
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/* fall through */
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case 1:
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a += ((uint32) k[0] << 24);
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/* case 0: nothing left to add */
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}
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#else /* !WORDS_BIGENDIAN */
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switch (len)
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{
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case 11:
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c += ((uint32) k[10] << 24);
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/* fall through */
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case 10:
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c += ((uint32) k[9] << 16);
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/* fall through */
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case 9:
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c += ((uint32) k[8] << 8);
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/* the lowest byte of c is reserved for the length */
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/* fall through */
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case 8:
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b += ka[1];
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a += ka[0];
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break;
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case 7:
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b += ((uint32) k[6] << 16);
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/* fall through */
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case 6:
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b += ((uint32) k[5] << 8);
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/* fall through */
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case 5:
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b += k[4];
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/* fall through */
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case 4:
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a += ka[0];
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break;
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case 3:
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a += ((uint32) k[2] << 16);
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/* fall through */
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case 2:
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a += ((uint32) k[1] << 8);
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/* fall through */
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case 1:
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a += k[0];
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/* case 0: nothing left to add */
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}
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#endif /* WORDS_BIGENDIAN */
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}
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else
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{
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/* Code path for non-aligned source data */
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/* handle most of the key */
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while (len >= 12)
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{
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#ifdef WORDS_BIGENDIAN
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a += (k[3] + ((uint32) k[2] << 8) + ((uint32) k[1] << 16) + ((uint32) k[0] << 24));
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b += (k[7] + ((uint32) k[6] << 8) + ((uint32) k[5] << 16) + ((uint32) k[4] << 24));
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c += (k[11] + ((uint32) k[10] << 8) + ((uint32) k[9] << 16) + ((uint32) k[8] << 24));
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#else /* !WORDS_BIGENDIAN */
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a += (k[0] + ((uint32) k[1] << 8) + ((uint32) k[2] << 16) + ((uint32) k[3] << 24));
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b += (k[4] + ((uint32) k[5] << 8) + ((uint32) k[6] << 16) + ((uint32) k[7] << 24));
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c += (k[8] + ((uint32) k[9] << 8) + ((uint32) k[10] << 16) + ((uint32) k[11] << 24));
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#endif /* WORDS_BIGENDIAN */
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mix(a, b, c);
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k += 12;
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len -= 12;
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}
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/* handle the last 11 bytes */
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#ifdef WORDS_BIGENDIAN
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switch (len) /* all the case statements fall through */
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{
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case 11:
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c += ((uint32) k[10] << 8);
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case 10:
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c += ((uint32) k[9] << 16);
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case 9:
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c += ((uint32) k[8] << 24);
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/* the lowest byte of c is reserved for the length */
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case 8:
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b += k[7];
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case 7:
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b += ((uint32) k[6] << 8);
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case 6:
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b += ((uint32) k[5] << 16);
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case 5:
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b += ((uint32) k[4] << 24);
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case 4:
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a += k[3];
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case 3:
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a += ((uint32) k[2] << 8);
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case 2:
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a += ((uint32) k[1] << 16);
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case 1:
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a += ((uint32) k[0] << 24);
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/* case 0: nothing left to add */
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}
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#else /* !WORDS_BIGENDIAN */
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switch (len) /* all the case statements fall through */
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{
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case 11:
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c += ((uint32) k[10] << 24);
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case 10:
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c += ((uint32) k[9] << 16);
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case 9:
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c += ((uint32) k[8] << 8);
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/* the lowest byte of c is reserved for the length */
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case 8:
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b += ((uint32) k[7] << 24);
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case 7:
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b += ((uint32) k[6] << 16);
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case 6:
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b += ((uint32) k[5] << 8);
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case 5:
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b += k[4];
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case 4:
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a += ((uint32) k[3] << 24);
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case 3:
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a += ((uint32) k[2] << 16);
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case 2:
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a += ((uint32) k[1] << 8);
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case 1:
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a += k[0];
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/* case 0: nothing left to add */
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}
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#endif /* WORDS_BIGENDIAN */
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}
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final(a, b, c);
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/* report the result */
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return UInt32GetDatum(c);
|
|
}
|
|
|
|
/*
|
|
* hash_uint32() -- hash a 32-bit value
|
|
*
|
|
* This has the same result as
|
|
* hash_any(&k, sizeof(uint32))
|
|
* but is faster and doesn't force the caller to store k into memory.
|
|
*/
|
|
Datum
|
|
hash_uint32(uint32 k)
|
|
{
|
|
register uint32 a,
|
|
b,
|
|
c;
|
|
|
|
a = b = c = 0x9e3779b9 + (uint32) sizeof(uint32) + 3923095;
|
|
a += k;
|
|
|
|
final(a, b, c);
|
|
|
|
/* report the result */
|
|
return UInt32GetDatum(c);
|
|
}
|