postgres.h

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/*-------------------------------------------------------------------------
 *
 * postgres.h
 *    Primary include file for PostgreSQL server .c files
 *
 * This should be the first file included by PostgreSQL backend modules.
 * Client-side code should include postgres_fe.h instead.
 *
 *
 * Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
 * Portions Copyright (c) 1995, Regents of the University of California
 *
 * src/include/postgres.h
 *
 *-------------------------------------------------------------------------
 */
/*
 *----------------------------------------------------------------
 *   TABLE OF CONTENTS
 *
 *      When adding stuff to this file, please try to put stuff
 *      into the relevant section, or add new sections as appropriate.
 *
 *    section   description
 *    -------   ------------------------------------------------
 *      1)      variable-length datatypes (TOAST support)
 *      2)      Datum type + support macros
 *
 *   NOTES
 *
 *  In general, this file should contain declarations that are widely needed
 *  in the backend environment, but are of no interest outside the backend.
 *
 *  Simple type definitions live in c.h, where they are shared with
 *  postgres_fe.h.  We do that since those type definitions are needed by
 *  frontend modules that want to deal with binary data transmission to or
 *  from the backend.  Type definitions in this file should be for
 *  representations that never escape the backend, such as Datum or
 *  TOASTed varlena objects.
 *
 *----------------------------------------------------------------
 */
#ifndef POSTGRES_H
#define POSTGRES_H

#include "c.h"
#include "utils/elog.h"
#include "utils/palloc.h"

/* ----------------------------------------------------------------
 *              Section 1:  variable-length datatypes (TOAST support)
 * ----------------------------------------------------------------
 */

/*
 * struct varatt_external is a traditional "TOAST pointer", that is, the
 * information needed to fetch a Datum stored out-of-line in a TOAST table.
 * The data is compressed if and only if va_extsize < va_rawsize - VARHDRSZ.
 * This struct must not contain any padding, because we sometimes compare
 * these pointers using memcmp.
 *
 * Note that this information is stored unaligned within actual tuples, so
 * you need to memcpy from the tuple into a local struct variable before
 * you can look at these fields!  (The reason we use memcmp is to avoid
 * having to do that just to detect equality of two TOAST pointers...)
 */
typedef struct varatt_external
{
    int32       va_rawsize;     /* Original data size (includes header) */
    int32       va_extsize;     /* External saved size (doesn't) */
    Oid         va_valueid;     /* Unique ID of value within TOAST table */
    Oid         va_toastrelid;  /* RelID of TOAST table containing it */
}           varatt_external;

/*
 * struct varatt_indirect is a "TOAST pointer" representing an out-of-line
 * Datum that's stored in memory, not in an external toast relation.
 * The creator of such a Datum is entirely responsible that the referenced
 * storage survives for as long as referencing pointer Datums can exist.
 *
 * Note that just as for struct varatt_external, this struct is stored
 * unaligned within any containing tuple.
 */
typedef struct varatt_indirect
{
    struct varlena *pointer;    /* Pointer to in-memory varlena */
}           varatt_indirect;

/*
 * struct varatt_expanded is a "TOAST pointer" representing an out-of-line
 * Datum that is stored in memory, in some type-specific, not necessarily
 * physically contiguous format that is convenient for computation not
 * storage.  APIs for this, in particular the definition of struct
 * ExpandedObjectHeader, are in src/include/utils/expandeddatum.h.
 *
 * Note that just as for struct varatt_external, this struct is stored
 * unaligned within any containing tuple.
 */
typedef struct ExpandedObjectHeader ExpandedObjectHeader;

typedef struct varatt_expanded
{
    ExpandedObjectHeader *eohptr;
} varatt_expanded;

/*
 * Type tag for the various sorts of "TOAST pointer" datums.  The peculiar
 * value for VARTAG_ONDISK comes from a requirement for on-disk compatibility
 * with a previous notion that the tag field was the pointer datum's length.
 */
typedef enum vartag_external
{
    VARTAG_INDIRECT = 1,
    VARTAG_EXPANDED_RO = 2,
    VARTAG_EXPANDED_RW = 3,
    VARTAG_ONDISK = 18
} vartag_external;

/* this test relies on the specific tag values above */
#define VARTAG_IS_EXPANDED(tag) \
    (((tag) & ~1) == VARTAG_EXPANDED_RO)

#define VARTAG_SIZE(tag) \
    ((tag) == VARTAG_INDIRECT ? sizeof(varatt_indirect) : \
     VARTAG_IS_EXPANDED(tag) ? sizeof(varatt_expanded) : \
     (tag) == VARTAG_ONDISK ? sizeof(varatt_external) : \
     TrapMacro(true, "unrecognized TOAST vartag"))

/*
 * These structs describe the header of a varlena object that may have been
 * TOASTed.  Generally, don't reference these structs directly, but use the
 * macros below.
 *
 * We use separate structs for the aligned and unaligned cases because the
 * compiler might otherwise think it could generate code that assumes
 * alignment while touching fields of a 1-byte-header varlena.
 */
typedef union
{
    struct                      /* Normal varlena (4-byte length) */
    {
        uint32      va_header;
        char        va_data[FLEXIBLE_ARRAY_MEMBER];
    }           va_4byte;
    struct                      /* Compressed-in-line format */
    {
        uint32      va_header;
        uint32      va_rawsize; /* Original data size (excludes header) */
        char        va_data[FLEXIBLE_ARRAY_MEMBER]; /* Compressed data */
    }           va_compressed;
} varattrib_4b;

typedef struct
{
    uint8       va_header;
    char        va_data[FLEXIBLE_ARRAY_MEMBER]; /* Data begins here */
} varattrib_1b;

/* TOAST pointers are a subset of varattrib_1b with an identifying tag byte */
typedef struct
{
    uint8       va_header;      /* Always 0x80 or 0x01 */
    uint8       va_tag;         /* Type of datum */
    char        va_data[FLEXIBLE_ARRAY_MEMBER]; /* Type-specific data */
} varattrib_1b_e;

/*
 * Bit layouts for varlena headers on big-endian machines:
 *
 * 00xxxxxx 4-byte length word, aligned, uncompressed data (up to 1G)
 * 01xxxxxx 4-byte length word, aligned, *compressed* data (up to 1G)
 * 10000000 1-byte length word, unaligned, TOAST pointer
 * 1xxxxxxx 1-byte length word, unaligned, uncompressed data (up to 126b)
 *
 * Bit layouts for varlena headers on little-endian machines:
 *
 * xxxxxx00 4-byte length word, aligned, uncompressed data (up to 1G)
 * xxxxxx10 4-byte length word, aligned, *compressed* data (up to 1G)
 * 00000001 1-byte length word, unaligned, TOAST pointer
 * xxxxxxx1 1-byte length word, unaligned, uncompressed data (up to 126b)
 *
 * The "xxx" bits are the length field (which includes itself in all cases).
 * In the big-endian case we mask to extract the length, in the little-endian
 * case we shift.  Note that in both cases the flag bits are in the physically
 * first byte.  Also, it is not possible for a 1-byte length word to be zero;
 * this lets us disambiguate alignment padding bytes from the start of an
 * unaligned datum.  (We now *require* pad bytes to be filled with zero!)
 *
 * In TOAST pointers the va_tag field (see varattrib_1b_e) is used to discern
 * the specific type and length of the pointer datum.
 */

/*
 * Endian-dependent macros.  These are considered internal --- use the
 * external macros below instead of using these directly.
 *
 * Note: IS_1B is true for external toast records but VARSIZE_1B will return 0
 * for such records. Hence you should usually check for IS_EXTERNAL before
 * checking for IS_1B.
 */

#ifdef WORDS_BIGENDIAN

#define VARATT_IS_4B(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0x80) == 0x00)
#define VARATT_IS_4B_U(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0xC0) == 0x00)
#define VARATT_IS_4B_C(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0xC0) == 0x40)
#define VARATT_IS_1B(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0x80) == 0x80)
#define VARATT_IS_1B_E(PTR) \
    ((((varattrib_1b *) (PTR))->va_header) == 0x80)
#define VARATT_NOT_PAD_BYTE(PTR) \
    (*((uint8 *) (PTR)) != 0)

/* VARSIZE_4B() should only be used on known-aligned data */
#define VARSIZE_4B(PTR) \
    (((varattrib_4b *) (PTR))->va_4byte.va_header & 0x3FFFFFFF)
#define VARSIZE_1B(PTR) \
    (((varattrib_1b *) (PTR))->va_header & 0x7F)
#define VARTAG_1B_E(PTR) \
    (((varattrib_1b_e *) (PTR))->va_tag)

#define SET_VARSIZE_4B(PTR,len) \
    (((varattrib_4b *) (PTR))->va_4byte.va_header = (len) & 0x3FFFFFFF)
#define SET_VARSIZE_4B_C(PTR,len) \
    (((varattrib_4b *) (PTR))->va_4byte.va_header = ((len) & 0x3FFFFFFF) | 0x40000000)
#define SET_VARSIZE_1B(PTR,len) \
    (((varattrib_1b *) (PTR))->va_header = (len) | 0x80)
#define SET_VARTAG_1B_E(PTR,tag) \
    (((varattrib_1b_e *) (PTR))->va_header = 0x80, \
     ((varattrib_1b_e *) (PTR))->va_tag = (tag))
#else                           /* !WORDS_BIGENDIAN */

#define VARATT_IS_4B(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0x01) == 0x00)
#define VARATT_IS_4B_U(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0x03) == 0x00)
#define VARATT_IS_4B_C(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0x03) == 0x02)
#define VARATT_IS_1B(PTR) \
    ((((varattrib_1b *) (PTR))->va_header & 0x01) == 0x01)
#define VARATT_IS_1B_E(PTR) \
    ((((varattrib_1b *) (PTR))->va_header) == 0x01)
#define VARATT_NOT_PAD_BYTE(PTR) \
    (*((uint8 *) (PTR)) != 0)

/* VARSIZE_4B() should only be used on known-aligned data */
#define VARSIZE_4B(PTR) \
    ((((varattrib_4b *) (PTR))->va_4byte.va_header >> 2) & 0x3FFFFFFF)
#define VARSIZE_1B(PTR) \
    ((((varattrib_1b *) (PTR))->va_header >> 1) & 0x7F)
#define VARTAG_1B_E(PTR) \
    (((varattrib_1b_e *) (PTR))->va_tag)

#define SET_VARSIZE_4B(PTR,len) \
    (((varattrib_4b *) (PTR))->va_4byte.va_header = (((uint32) (len)) << 2))
#define SET_VARSIZE_4B_C(PTR,len) \
    (((varattrib_4b *) (PTR))->va_4byte.va_header = (((uint32) (len)) << 2) | 0x02)
#define SET_VARSIZE_1B(PTR,len) \
    (((varattrib_1b *) (PTR))->va_header = (((uint8) (len)) << 1) | 0x01)
#define SET_VARTAG_1B_E(PTR,tag) \
    (((varattrib_1b_e *) (PTR))->va_header = 0x01, \
     ((varattrib_1b_e *) (PTR))->va_tag = (tag))
#endif                          /* WORDS_BIGENDIAN */

#define VARHDRSZ_SHORT          offsetof(varattrib_1b, va_data)
#define VARATT_SHORT_MAX        0x7F
#define VARATT_CAN_MAKE_SHORT(PTR) \
    (VARATT_IS_4B_U(PTR) && \
     (VARSIZE(PTR) - VARHDRSZ + VARHDRSZ_SHORT) <= VARATT_SHORT_MAX)
#define VARATT_CONVERTED_SHORT_SIZE(PTR) \
    (VARSIZE(PTR) - VARHDRSZ + VARHDRSZ_SHORT)

#define VARHDRSZ_EXTERNAL       offsetof(varattrib_1b_e, va_data)

#define VARDATA_4B(PTR)     (((varattrib_4b *) (PTR))->va_4byte.va_data)
#define VARDATA_4B_C(PTR)   (((varattrib_4b *) (PTR))->va_compressed.va_data)
#define VARDATA_1B(PTR)     (((varattrib_1b *) (PTR))->va_data)
#define VARDATA_1B_E(PTR)   (((varattrib_1b_e *) (PTR))->va_data)

#define VARRAWSIZE_4B_C(PTR) \
    (((varattrib_4b *) (PTR))->va_compressed.va_rawsize)

/* Externally visible macros */

/*
 * In consumers oblivious to data alignment, call PG_DETOAST_DATUM_PACKED(),
 * VARDATA_ANY(), VARSIZE_ANY() and VARSIZE_ANY_EXHDR().  Elsewhere, call
 * PG_DETOAST_DATUM(), VARDATA() and VARSIZE().  Directly fetching an int16,
 * int32 or wider field in the struct representing the datum layout requires
 * aligned data.  memcpy() is alignment-oblivious, as are most operations on
 * datatypes, such as text, whose layout struct contains only char fields.
 *
 * Code assembling a new datum should call VARDATA() and SET_VARSIZE().
 * (Datums begin life untoasted.)
 *
 * Other macros here should usually be used only by tuple assembly/disassembly
 * code and code that specifically wants to work with still-toasted Datums.
 */
#define VARDATA(PTR)                        VARDATA_4B(PTR)
#define VARSIZE(PTR)                        VARSIZE_4B(PTR)

#define VARSIZE_SHORT(PTR)                  VARSIZE_1B(PTR)
#define VARDATA_SHORT(PTR)                  VARDATA_1B(PTR)

#define VARTAG_EXTERNAL(PTR)                VARTAG_1B_E(PTR)
#define VARSIZE_EXTERNAL(PTR)               (VARHDRSZ_EXTERNAL + VARTAG_SIZE(VARTAG_EXTERNAL(PTR)))
#define VARDATA_EXTERNAL(PTR)               VARDATA_1B_E(PTR)

#define VARATT_IS_COMPRESSED(PTR)           VARATT_IS_4B_C(PTR)
#define VARATT_IS_EXTERNAL(PTR)             VARATT_IS_1B_E(PTR)
#define VARATT_IS_EXTERNAL_ONDISK(PTR) \
    (VARATT_IS_EXTERNAL(PTR) && VARTAG_EXTERNAL(PTR) == VARTAG_ONDISK)
#define VARATT_IS_EXTERNAL_INDIRECT(PTR) \
    (VARATT_IS_EXTERNAL(PTR) && VARTAG_EXTERNAL(PTR) == VARTAG_INDIRECT)
#define VARATT_IS_EXTERNAL_EXPANDED_RO(PTR) \
    (VARATT_IS_EXTERNAL(PTR) && VARTAG_EXTERNAL(PTR) == VARTAG_EXPANDED_RO)
#define VARATT_IS_EXTERNAL_EXPANDED_RW(PTR) \
    (VARATT_IS_EXTERNAL(PTR) && VARTAG_EXTERNAL(PTR) == VARTAG_EXPANDED_RW)
#define VARATT_IS_EXTERNAL_EXPANDED(PTR) \
    (VARATT_IS_EXTERNAL(PTR) && VARTAG_IS_EXPANDED(VARTAG_EXTERNAL(PTR)))
#define VARATT_IS_EXTERNAL_NON_EXPANDED(PTR) \
    (VARATT_IS_EXTERNAL(PTR) && !VARTAG_IS_EXPANDED(VARTAG_EXTERNAL(PTR)))
#define VARATT_IS_SHORT(PTR)                VARATT_IS_1B(PTR)
#define VARATT_IS_EXTENDED(PTR)             (!VARATT_IS_4B_U(PTR))

#define SET_VARSIZE(PTR, len)               SET_VARSIZE_4B(PTR, len)
#define SET_VARSIZE_SHORT(PTR, len)         SET_VARSIZE_1B(PTR, len)
#define SET_VARSIZE_COMPRESSED(PTR, len)    SET_VARSIZE_4B_C(PTR, len)

#define SET_VARTAG_EXTERNAL(PTR, tag)       SET_VARTAG_1B_E(PTR, tag)

#define VARSIZE_ANY(PTR) \
    (VARATT_IS_1B_E(PTR) ? VARSIZE_EXTERNAL(PTR) : \
     (VARATT_IS_1B(PTR) ? VARSIZE_1B(PTR) : \
      VARSIZE_4B(PTR)))

/* Size of a varlena data, excluding header */
#define VARSIZE_ANY_EXHDR(PTR) \
    (VARATT_IS_1B_E(PTR) ? VARSIZE_EXTERNAL(PTR)-VARHDRSZ_EXTERNAL : \
     (VARATT_IS_1B(PTR) ? VARSIZE_1B(PTR)-VARHDRSZ_SHORT : \
      VARSIZE_4B(PTR)-VARHDRSZ))

/* caution: this will not work on an external or compressed-in-line Datum */
/* caution: this will return a possibly unaligned pointer */
#define VARDATA_ANY(PTR) \
     (VARATT_IS_1B(PTR) ? VARDATA_1B(PTR) : VARDATA_4B(PTR))


/* ----------------------------------------------------------------
 *              Section 2:  Datum type + support macros
 * ----------------------------------------------------------------
 */

/*
 * A Datum contains either a value of a pass-by-value type or a pointer to a
 * value of a pass-by-reference type.  Therefore, we require:
 *
 * sizeof(Datum) == sizeof(void *) == 4 or 8
 *
 * The macros below and the analogous macros for other types should be used to
 * convert between a Datum and the appropriate C type.
 */

typedef uintptr_t Datum;

#define SIZEOF_DATUM SIZEOF_VOID_P

/*
 * DatumGetBool
 *      Returns boolean value of a datum.
 *
 * Note: any nonzero value will be considered true.
 */

#define DatumGetBool(X) ((bool) ((X) != 0))

/*
 * BoolGetDatum
 *      Returns datum representation for a boolean.
 *
 * Note: any nonzero value will be considered true.
 */

#define BoolGetDatum(X) ((Datum) ((X) ? 1 : 0))

/*
 * DatumGetChar
 *      Returns character value of a datum.
 */

#define DatumGetChar(X) ((char) (X))

/*
 * CharGetDatum
 *      Returns datum representation for a character.
 */

#define CharGetDatum(X) ((Datum) (X))

/*
 * Int8GetDatum
 *      Returns datum representation for an 8-bit integer.
 */

#define Int8GetDatum(X) ((Datum) (X))

/*
 * DatumGetUInt8
 *      Returns 8-bit unsigned integer value of a datum.
 */

#define DatumGetUInt8(X) ((uint8) (X))

/*
 * UInt8GetDatum
 *      Returns datum representation for an 8-bit unsigned integer.
 */

#define UInt8GetDatum(X) ((Datum) (X))

/*
 * DatumGetInt16
 *      Returns 16-bit integer value of a datum.
 */

#define DatumGetInt16(X) ((int16) (X))

/*
 * Int16GetDatum
 *      Returns datum representation for a 16-bit integer.
 */

#define Int16GetDatum(X) ((Datum) (X))

/*
 * DatumGetUInt16
 *      Returns 16-bit unsigned integer value of a datum.
 */

#define DatumGetUInt16(X) ((uint16) (X))

/*
 * UInt16GetDatum
 *      Returns datum representation for a 16-bit unsigned integer.
 */

#define UInt16GetDatum(X) ((Datum) (X))

/*
 * DatumGetInt32
 *      Returns 32-bit integer value of a datum.
 */

#define DatumGetInt32(X) ((int32) (X))

/*
 * Int32GetDatum
 *      Returns datum representation for a 32-bit integer.
 */

#define Int32GetDatum(X) ((Datum) (X))

/*
 * DatumGetUInt32
 *      Returns 32-bit unsigned integer value of a datum.
 */

#define DatumGetUInt32(X) ((uint32) (X))

/*
 * UInt32GetDatum
 *      Returns datum representation for a 32-bit unsigned integer.
 */

#define UInt32GetDatum(X) ((Datum) (X))

/*
 * DatumGetObjectId
 *      Returns object identifier value of a datum.
 */

#define DatumGetObjectId(X) ((Oid) (X))

/*
 * ObjectIdGetDatum
 *      Returns datum representation for an object identifier.
 */

#define ObjectIdGetDatum(X) ((Datum) (X))

/*
 * DatumGetTransactionId
 *      Returns transaction identifier value of a datum.
 */

#define DatumGetTransactionId(X) ((TransactionId) (X))

/*
 * TransactionIdGetDatum
 *      Returns datum representation for a transaction identifier.
 */

#define TransactionIdGetDatum(X) ((Datum) (X))

/*
 * MultiXactIdGetDatum
 *      Returns datum representation for a multixact identifier.
 */

#define MultiXactIdGetDatum(X) ((Datum) (X))

/*
 * DatumGetCommandId
 *      Returns command identifier value of a datum.
 */

#define DatumGetCommandId(X) ((CommandId) (X))

/*
 * CommandIdGetDatum
 *      Returns datum representation for a command identifier.
 */

#define CommandIdGetDatum(X) ((Datum) (X))

/*
 * DatumGetPointer
 *      Returns pointer value of a datum.
 */

#define DatumGetPointer(X) ((Pointer) (X))

/*
 * PointerGetDatum
 *      Returns datum representation for a pointer.
 */

#define PointerGetDatum(X) ((Datum) (X))

/*
 * DatumGetCString
 *      Returns C string (null-terminated string) value of a datum.
 *
 * Note: C string is not a full-fledged Postgres type at present,
 * but type input functions use this conversion for their inputs.
 */

#define DatumGetCString(X) ((char *) DatumGetPointer(X))

/*
 * CStringGetDatum
 *      Returns datum representation for a C string (null-terminated string).
 *
 * Note: C string is not a full-fledged Postgres type at present,
 * but type output functions use this conversion for their outputs.
 * Note: CString is pass-by-reference; caller must ensure the pointed-to
 * value has adequate lifetime.
 */

#define CStringGetDatum(X) PointerGetDatum(X)

/*
 * DatumGetName
 *      Returns name value of a datum.
 */

#define DatumGetName(X) ((Name) DatumGetPointer(X))

/*
 * NameGetDatum
 *      Returns datum representation for a name.
 *
 * Note: Name is pass-by-reference; caller must ensure the pointed-to
 * value has adequate lifetime.
 */

#define NameGetDatum(X) CStringGetDatum(NameStr(*(X)))

/*
 * DatumGetInt64
 *      Returns 64-bit integer value of a datum.
 *
 * Note: this macro hides whether int64 is pass by value or by reference.
 */

#ifdef USE_FLOAT8_BYVAL
#define DatumGetInt64(X) ((int64) (X))
#else
#define DatumGetInt64(X) (* ((int64 *) DatumGetPointer(X)))
#endif

/*
 * Int64GetDatum
 *      Returns datum representation for a 64-bit integer.
 *
 * Note: if int64 is pass by reference, this function returns a reference
 * to palloc'd space.
 */

#ifdef USE_FLOAT8_BYVAL
#define Int64GetDatum(X) ((Datum) (X))
#else
extern Datum Int64GetDatum(int64 X);
#endif

/*
 * DatumGetUInt64
 *      Returns 64-bit unsigned integer value of a datum.
 *
 * Note: this macro hides whether int64 is pass by value or by reference.
 */

#ifdef USE_FLOAT8_BYVAL
#define DatumGetUInt64(X) ((uint64) (X))
#else
#define DatumGetUInt64(X) (* ((uint64 *) DatumGetPointer(X)))
#endif

/*
 * UInt64GetDatum
 *      Returns datum representation for a 64-bit unsigned integer.
 *
 * Note: if int64 is pass by reference, this function returns a reference
 * to palloc'd space.
 */

#ifdef USE_FLOAT8_BYVAL
#define UInt64GetDatum(X) ((Datum) (X))
#else
#define UInt64GetDatum(X) Int64GetDatum((int64) (X))
#endif

/*
 * Float <-> Datum conversions
 *
 * These have to be implemented as inline functions rather than macros, when
 * passing by value, because many machines pass int and float function
 * parameters/results differently; so we need to play weird games with unions.
 */

/*
 * DatumGetFloat4
 *      Returns 4-byte floating point value of a datum.
 *
 * Note: this macro hides whether float4 is pass by value or by reference.
 */

#ifdef USE_FLOAT4_BYVAL
static inline float4
DatumGetFloat4(Datum X)
{
    union
    {
        int32       value;
        float4      retval;
    }           myunion;

    myunion.value = DatumGetInt32(X);
    return myunion.retval;
}
#else
#define DatumGetFloat4(X) (* ((float4 *) DatumGetPointer(X)))
#endif

/*
 * Float4GetDatum
 *      Returns datum representation for a 4-byte floating point number.
 *
 * Note: if float4 is pass by reference, this function returns a reference
 * to palloc'd space.
 */
#ifdef USE_FLOAT4_BYVAL
static inline Datum
Float4GetDatum(float4 X)
{
    union
    {
        float4      value;
        int32       retval;
    }           myunion;

    myunion.value = X;
    return Int32GetDatum(myunion.retval);
}
#else
extern Datum Float4GetDatum(float4 X);
#endif

/*
 * DatumGetFloat8
 *      Returns 8-byte floating point value of a datum.
 *
 * Note: this macro hides whether float8 is pass by value or by reference.
 */

#ifdef USE_FLOAT8_BYVAL
static inline float8
DatumGetFloat8(Datum X)
{
    union
    {
        int64       value;
        float8      retval;
    }           myunion;

    myunion.value = DatumGetInt64(X);
    return myunion.retval;
}
#else
#define DatumGetFloat8(X) (* ((float8 *) DatumGetPointer(X)))
#endif

/*
 * Float8GetDatum
 *      Returns datum representation for an 8-byte floating point number.
 *
 * Note: if float8 is pass by reference, this function returns a reference
 * to palloc'd space.
 */

#ifdef USE_FLOAT8_BYVAL
static inline Datum
Float8GetDatum(float8 X)
{
    union
    {
        float8      value;
        int64       retval;
    }           myunion;

    myunion.value = X;
    return Int64GetDatum(myunion.retval);
}
#else
extern Datum Float8GetDatum(float8 X);
#endif


/*
 * Int64GetDatumFast
 * Float8GetDatumFast
 * Float4GetDatumFast
 *
 * These macros are intended to allow writing code that does not depend on
 * whether int64, float8, float4 are pass-by-reference types, while not
 * sacrificing performance when they are.  The argument must be a variable
 * that will exist and have the same value for as long as the Datum is needed.
 * In the pass-by-ref case, the address of the variable is taken to use as
 * the Datum.  In the pass-by-val case, these will be the same as the non-Fast
 * macros.
 */

#ifdef USE_FLOAT8_BYVAL
#define Int64GetDatumFast(X)  Int64GetDatum(X)
#define Float8GetDatumFast(X) Float8GetDatum(X)
#else
#define Int64GetDatumFast(X)  PointerGetDatum(&(X))
#define Float8GetDatumFast(X) PointerGetDatum(&(X))
#endif

#ifdef USE_FLOAT4_BYVAL
#define Float4GetDatumFast(X) Float4GetDatum(X)
#else
#define Float4GetDatumFast(X) PointerGetDatum(&(X))
#endif

#endif                          /* POSTGRES_H */