hashfunc.c

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/*-------------------------------------------------------------------------
 *
 * hashfunc.c
 *    Support functions for hash access method.
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/access/hash/hashfunc.c
 *
 * NOTES
 *    These functions are stored in pg_amproc.  For each operator class
 *    defined for hash indexes, they compute the hash value of the argument.
 *
 *    Additional hash functions appear in /utils/adt/ files for various
 *    specialized datatypes.
 *
 *    It is expected that every bit of a hash function's 32-bit result is
 *    as random as every other; failure to ensure this is likely to lead
 *    to poor performance of hash joins, for example.  In most cases a hash
 *    function should use hash_any() or its variant hash_uint32().
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "access/hash.h"
#include "catalog/pg_collation.h"
#include "common/hashfn.h"
#include "utils/builtins.h"
#include "utils/float.h"
#include "utils/pg_locale.h"
#include "varatt.h"
 
/*
 * Datatype-specific hash functions.
 *
 * These support both hash indexes and hash joins.
 *
 * NOTE: some of these are also used by catcache operations, without
 * any direct connection to hash indexes.  Also, the common hash_any
 * routine is also used by dynahash tables.
 */
 
/* Note: this is used for both "char" and boolean datatypes */
Datum
hashchar(PG_FUNCTION_ARGS)
{
    return hash_uint32((int32) PG_GETARG_CHAR(0));
}
 
Datum
hashcharextended(PG_FUNCTION_ARGS)
{
    return hash_uint32_extended((int32) PG_GETARG_CHAR(0), PG_GETARG_INT64(1));
}
 
Datum
hashint2(PG_FUNCTION_ARGS)
{
    return hash_uint32((int32) PG_GETARG_INT16(0));
}
 
Datum
hashint2extended(PG_FUNCTION_ARGS)
{
    return hash_uint32_extended((int32) PG_GETARG_INT16(0), PG_GETARG_INT64(1));
}
 
Datum
hashint4(PG_FUNCTION_ARGS)
{
    return hash_uint32(PG_GETARG_INT32(0));
}
 
Datum
hashint4extended(PG_FUNCTION_ARGS)
{
    return hash_uint32_extended(PG_GETARG_INT32(0), PG_GETARG_INT64(1));
}
 
Datum
hashint8(PG_FUNCTION_ARGS)
{
    /*
     * The idea here is to produce a hash value compatible with the values
     * produced by hashint4 and hashint2 for logically equal inputs; this is
     * necessary to support cross-type hash joins across these input types.
     * Since all three types are signed, we can xor the high half of the int8
     * value if the sign is positive, or the complement of the high half when
     * the sign is negative.
     */
    int64       val = PG_GETARG_INT64(0);
    uint32      lohalf = (uint32) val;
    uint32      hihalf = (uint32) (val >> 32);
 
    lohalf ^= (val >= 0) ? hihalf : ~hihalf;
 
    return hash_uint32(lohalf);
}
 
Datum
hashint8extended(PG_FUNCTION_ARGS)
{
    /* Same approach as hashint8 */
    int64       val = PG_GETARG_INT64(0);
    uint32      lohalf = (uint32) val;
    uint32      hihalf = (uint32) (val >> 32);
 
    lohalf ^= (val >= 0) ? hihalf : ~hihalf;
 
    return hash_uint32_extended(lohalf, PG_GETARG_INT64(1));
}
 
Datum
hashoid(PG_FUNCTION_ARGS)
{
    return hash_uint32((uint32) PG_GETARG_OID(0));
}
 
Datum
hashoidextended(PG_FUNCTION_ARGS)
{
    return hash_uint32_extended((uint32) PG_GETARG_OID(0), PG_GETARG_INT64(1));
}
 
Datum
hashenum(PG_FUNCTION_ARGS)
{
    return hash_uint32((uint32) PG_GETARG_OID(0));
}
 
Datum
hashenumextended(PG_FUNCTION_ARGS)
{
    return hash_uint32_extended((uint32) PG_GETARG_OID(0), PG_GETARG_INT64(1));
}
 
Datum
hashfloat4(PG_FUNCTION_ARGS)
{
    float4      key = PG_GETARG_FLOAT4(0);
    float8      key8;
 
    /*
     * On IEEE-float machines, minus zero and zero have different bit patterns
     * but should compare as equal.  We must ensure that they have the same
     * hash value, which is most reliably done this way:
     */
    if (key == (float4) 0)
        PG_RETURN_UINT32(0);
 
    /*
     * To support cross-type hashing of float8 and float4, we want to return
     * the same hash value hashfloat8 would produce for an equal float8 value.
     * So, widen the value to float8 and hash that.  (We must do this rather
     * than have hashfloat8 try to narrow its value to float4; that could fail
     * on overflow.)
     */
    key8 = key;
 
    /*
     * Similarly, NaNs can have different bit patterns but they should all
     * compare as equal.  For backwards-compatibility reasons we force them to
     * have the hash value of a standard float8 NaN.  (You'd think we could
     * replace key with a float4 NaN and then widen it; but on some old
     * platforms, that way produces a different bit pattern.)
     */
    if (isnan(key8))
        key8 = get_float8_nan();
 
    return hash_any((unsigned char *) &key8, sizeof(key8));
}
 
Datum
hashfloat4extended(PG_FUNCTION_ARGS)
{
    float4      key = PG_GETARG_FLOAT4(0);
    uint64      seed = PG_GETARG_INT64(1);
    float8      key8;
 
    /* Same approach as hashfloat4 */
    if (key == (float4) 0)
        PG_RETURN_UINT64(seed);
    key8 = key;
    if (isnan(key8))
        key8 = get_float8_nan();
 
    return hash_any_extended((unsigned char *) &key8, sizeof(key8), seed);
}
 
Datum
hashfloat8(PG_FUNCTION_ARGS)
{
    float8      key = PG_GETARG_FLOAT8(0);
 
    /*
     * On IEEE-float machines, minus zero and zero have different bit patterns
     * but should compare as equal.  We must ensure that they have the same
     * hash value, which is most reliably done this way:
     */
    if (key == (float8) 0)
        PG_RETURN_UINT32(0);
 
    /*
     * Similarly, NaNs can have different bit patterns but they should all
     * compare as equal.  For backwards-compatibility reasons we force them to
     * have the hash value of a standard NaN.
     */
    if (isnan(key))
        key = get_float8_nan();
 
    return hash_any((unsigned char *) &key, sizeof(key));
}
 
Datum
hashfloat8extended(PG_FUNCTION_ARGS)
{
    float8      key = PG_GETARG_FLOAT8(0);
    uint64      seed = PG_GETARG_INT64(1);
 
    /* Same approach as hashfloat8 */
    if (key == (float8) 0)
        PG_RETURN_UINT64(seed);
    if (isnan(key))
        key = get_float8_nan();
 
    return hash_any_extended((unsigned char *) &key, sizeof(key), seed);
}
 
Datum
hashoidvector(PG_FUNCTION_ARGS)
{
    oidvector  *key = (oidvector *) PG_GETARG_POINTER(0);
 
    return hash_any((unsigned char *) key->values, key->dim1 * sizeof(Oid));
}
 
Datum
hashoidvectorextended(PG_FUNCTION_ARGS)
{
    oidvector  *key = (oidvector *) PG_GETARG_POINTER(0);
 
    return hash_any_extended((unsigned char *) key->values,
                             key->dim1 * sizeof(Oid),
                             PG_GETARG_INT64(1));
}
 
Datum
hashname(PG_FUNCTION_ARGS)
{
    char       *key = NameStr(*PG_GETARG_NAME(0));
 
    return hash_any((unsigned char *) key, strlen(key));
}
 
Datum
hashnameextended(PG_FUNCTION_ARGS)
{
    char       *key = NameStr(*PG_GETARG_NAME(0));
 
    return hash_any_extended((unsigned char *) key, strlen(key),
                             PG_GETARG_INT64(1));
}
 
Datum
hashtext(PG_FUNCTION_ARGS)
{
    text       *key = PG_GETARG_TEXT_PP(0);
    Oid         collid = PG_GET_COLLATION();
    pg_locale_t mylocale = 0;
    Datum       result;
 
    if (!collid)
        ereport(ERROR,
                (errcode(ERRCODE_INDETERMINATE_COLLATION),
                 errmsg("could not determine which collation to use for string hashing"),
                 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
    if (!lc_collate_is_c(collid))
        mylocale = pg_newlocale_from_collation(collid);
 
    if (pg_locale_deterministic(mylocale))
    {
        result = hash_any((unsigned char *) VARDATA_ANY(key),
                          VARSIZE_ANY_EXHDR(key));
    }
    else
    {
        Size        bsize,
                    rsize;
        char       *buf;
        const char *keydata = VARDATA_ANY(key);
        size_t      keylen = VARSIZE_ANY_EXHDR(key);
 
 
        bsize = pg_strnxfrm(NULL, 0, keydata, keylen, mylocale);
        buf = palloc(bsize + 1);
 
        rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
        if (rsize != bsize)
            elog(ERROR, "pg_strnxfrm() returned unexpected result");
 
        /*
         * In principle, there's no reason to include the terminating NUL
         * character in the hash, but it was done before and the behavior must
         * be preserved.
         */
        result = hash_any((uint8_t *) buf, bsize + 1);
 
        pfree(buf);
    }
 
    /* Avoid leaking memory for toasted inputs */
    PG_FREE_IF_COPY(key, 0);
 
    return result;
}
 
Datum
hashtextextended(PG_FUNCTION_ARGS)
{
    text       *key = PG_GETARG_TEXT_PP(0);
    Oid         collid = PG_GET_COLLATION();
    pg_locale_t mylocale = 0;
    Datum       result;
 
    if (!collid)
        ereport(ERROR,
                (errcode(ERRCODE_INDETERMINATE_COLLATION),
                 errmsg("could not determine which collation to use for string hashing"),
                 errhint("Use the COLLATE clause to set the collation explicitly.")));
 
    if (!lc_collate_is_c(collid))
        mylocale = pg_newlocale_from_collation(collid);
 
    if (pg_locale_deterministic(mylocale))
    {
        result = hash_any_extended((unsigned char *) VARDATA_ANY(key),
                                   VARSIZE_ANY_EXHDR(key),
                                   PG_GETARG_INT64(1));
    }
    else
    {
        Size        bsize,
                    rsize;
        char       *buf;
        const char *keydata = VARDATA_ANY(key);
        size_t      keylen = VARSIZE_ANY_EXHDR(key);
 
        bsize = pg_strnxfrm(NULL, 0, keydata, keylen, mylocale);
        buf = palloc(bsize + 1);
 
        rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
        if (rsize != bsize)
            elog(ERROR, "pg_strnxfrm() returned unexpected result");
 
        /*
         * In principle, there's no reason to include the terminating NUL
         * character in the hash, but it was done before and the behavior must
         * be preserved.
         */
        result = hash_any_extended((uint8_t *) buf, bsize + 1,
                                   PG_GETARG_INT64(1));
 
        pfree(buf);
    }
 
    PG_FREE_IF_COPY(key, 0);
 
    return result;
}
 
/*
 * hashvarlena() can be used for any varlena datatype in which there are
 * no non-significant bits, ie, distinct bitpatterns never compare as equal.
 */
Datum
hashvarlena(PG_FUNCTION_ARGS)
{
    struct varlena *key = PG_GETARG_VARLENA_PP(0);
    Datum       result;
 
    result = hash_any((unsigned char *) VARDATA_ANY(key),
                      VARSIZE_ANY_EXHDR(key));
 
    /* Avoid leaking memory for toasted inputs */
    PG_FREE_IF_COPY(key, 0);
 
    return result;
}
 
Datum
hashvarlenaextended(PG_FUNCTION_ARGS)
{
    struct varlena *key = PG_GETARG_VARLENA_PP(0);
    Datum       result;
 
    result = hash_any_extended((unsigned char *) VARDATA_ANY(key),
                               VARSIZE_ANY_EXHDR(key),
                               PG_GETARG_INT64(1));
 
    PG_FREE_IF_COPY(key, 0);
 
    return result;
}