tupmacs.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * tupmacs.h
 *    Tuple macros used by both index tuples and heap tuples.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/access/tupmacs.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef TUPMACS_H
#define TUPMACS_H
 
#include "catalog/pg_type_d.h"  /* for TYPALIGN macros */
#include "port/pg_bitutils.h"
#include "port/pg_bswap.h"
#include "varatt.h"
 
/*
 * Check a tuple's null bitmap to determine whether the attribute is null.
 * Note that a 0 in the null bitmap indicates a null, while 1 indicates
 * non-null.
 */
static inline bool
att_isnull(int ATT, const uint8 *BITS)
{
    return !(BITS[ATT >> 3] & (1 << (ATT & 0x07)));
}
 
/*
 * populate_isnull_array
 *      Transform a tuple's null bitmap into a boolean array.
 *
 * Caller must ensure that the isnull array is sized so it contains
 * at least as many elements as there are bits in the 'bits' array.
 * Callers should be aware that isnull is populated 8 elements at a time,
 * effectively as if natts is rounded up to the next multiple of 8.
 */
static inline void
populate_isnull_array(const uint8 *bits, int natts, bool *isnull)
{
    int         nbytes = (natts + 7) >> 3;
 
    /*
     * Multiplying the inverted NULL bitmap byte by this value results in the
     * lowest bit in each byte being set the same as each bit of the inverted
     * byte.  We perform this as 2 32-bit operations rather than a single
     * 64-bit operation as multiplying by the required value to do this in
     * 64-bits would result in overflowing a uint64 in some cases.
     *
     * XXX if we ever require BMI2 (-march=x86-64-v3), then this could be done
     * more efficiently on most X86-64 CPUs with the PDEP instruction.  Beware
     * that some chips (e.g. AMD's Zen2) are horribly inefficient at PDEP.
     */
#define SPREAD_BITS_MULTIPLIER_32 0x204081U
 
    for (int i = 0; i < nbytes; i++, isnull += 8)
    {
        uint64      isnull_8;
        uint8       nullbyte = ~bits[i];
 
        /* Convert the lower 4 bits of NULL bitmap word into a 64 bit int */
        isnull_8 = (nullbyte & 0xf) * SPREAD_BITS_MULTIPLIER_32;
 
        /*
         * Convert the upper 4 bits of NULL bitmap word into a 64 bit int,
         * shift into the upper 32 bit and bitwise-OR with the result of the
         * lower 4 bits.
         */
        isnull_8 |= ((uint64) ((nullbyte >> 4) * SPREAD_BITS_MULTIPLIER_32)) << 32;
 
        /* Mask out all other bits apart from the lowest bit of each byte. */
        isnull_8 &= UINT64CONST(0x0101010101010101);
 
#ifdef WORDS_BIGENDIAN
 
        /*
         * Fix byte order on big-endian machines before copying to the array.
         */
        isnull_8 = pg_bswap64(isnull_8);
#endif
        memcpy(isnull, &isnull_8, sizeof(uint64));
    }
}
 
#ifndef FRONTEND
/*
 * Given an attbyval and an attlen from either a Form_pg_attribute or
 * CompactAttribute and a pointer into a tuple's data area, return the
 * correct value or pointer.
 *
 * We return a Datum value in all cases.  If attbyval is false,  we return the
 * same pointer into the tuple data area that we're passed.  Otherwise, we
 * return the correct number of bytes fetched from the data area and extended
 * to Datum form.
 *
 * Note that T must already be properly aligned for this to work correctly.
 */
#define fetchatt(A,T) fetch_att(T, (A)->attbyval, (A)->attlen)
 
/*
 * Same, but work from byval/len parameters rather than Form_pg_attribute.
 */
static inline Datum
fetch_att(const void *T, bool attbyval, int attlen)
{
    if (attbyval)
    {
        switch (attlen)
        {
            case sizeof(char):
                return CharGetDatum(*((const char *) T));
            case sizeof(int16):
                return Int16GetDatum(*((const int16 *) T));
            case sizeof(int32):
                return Int32GetDatum(*((const int32 *) T));
            case sizeof(int64):
                return Int64GetDatum(*((const int64 *) T));
            default:
                elog(ERROR, "unsupported byval length: %d", attlen);
                return 0;
        }
    }
    else
        return PointerGetDatum(T);
}
 
/*
 * Same as fetch_att, but no error checking for invalid attlens for byval
 * types.  This is safe to use when attlen comes from CompactAttribute as we
 * validate the length when populating that struct.
 */
static inline Datum
fetch_att_noerr(const void *T, bool attbyval, int attlen)
{
    if (attbyval)
    {
        switch (attlen)
        {
            case sizeof(int32):
                return Int32GetDatum(*((const int32 *) T));
            case sizeof(int16):
                return Int16GetDatum(*((const int16 *) T));
            case sizeof(char):
                return CharGetDatum(*((const char *) T));
            default:
                Assert(attlen == sizeof(int64));
                return Int64GetDatum(*((const int64 *) T));
        }
    }
    else
        return PointerGetDatum(T);
}
 
 
/*
 * align_fetch_then_add
 *      Applies all the functionality of att_pointer_alignby(),
 *      fetch_att_noerr() and att_addlength_pointer(), resulting in the *off
 *      pointer to the perhaps unaligned number of bytes into 'tupptr', ready
 *      to deform the next attribute.
 *
 * tupptr: pointer to the beginning of the tuple, after the header and any
 * NULL bitmask.
 * off: offset in bytes for reading tuple data, possibly unaligned.
 * attbyval, attlen and attalignby are values from CompactAttribute.
 */
static inline Datum
align_fetch_then_add(const char *tupptr, uint32 *off, bool attbyval, int attlen,
                     uint8 attalignby)
{
    Datum       res;
 
    if (attlen > 0)
    {
        const char *offset_ptr;
 
        *off = TYPEALIGN(attalignby, *off);
        offset_ptr = tupptr + *off;
        *off += attlen;
        if (attbyval)
        {
            switch (attlen)
            {
                case sizeof(char):
                    return CharGetDatum(*((const char *) offset_ptr));
                case sizeof(int16):
                    return Int16GetDatum(*((const int16 *) offset_ptr));
                case sizeof(int32):
                    return Int32GetDatum(*((const int32 *) offset_ptr));
                default:
 
                    /*
                     * populate_compact_attribute_internal() should have
                     * checked
                     */
                    Assert(attlen == sizeof(int64));
                    return Int64GetDatum(*((const int64 *) offset_ptr));
            }
        }
        return PointerGetDatum(offset_ptr);
    }
    else if (attlen == -1)
    {
        if (!VARATT_IS_SHORT(tupptr + *off))
            *off = TYPEALIGN(attalignby, *off);
 
        res = PointerGetDatum(tupptr + *off);
        *off += VARSIZE_ANY(DatumGetPointer(res));
        return res;
    }
    else
    {
        Assert(attlen == -2);
        *off = TYPEALIGN(attalignby, *off);
        res = PointerGetDatum(tupptr + *off);
        *off += strlen(tupptr + *off) + 1;
        return res;
    }
}
 
/*
 * first_null_attr
 *      Inspect a NULL bitmap from a tuple and return the 0-based attnum of the
 *      first NULL attribute.  Returns natts if no NULLs were found.
 *
 * This is coded to expect that 'bits' contains at least one 0 bit somewhere
 * in the array, but not necessarily < natts.  Note that natts may be passed
 * as a value lower than the number of bits physically stored in the tuple's
 * NULL bitmap, in which case we may not find a NULL and return natts.
 *
 * The reason we require at least one 0 bit somewhere in the NULL bitmap is
 * that the for loop that checks 0xFF bytes would loop to the last byte in
 * the array if all bytes were 0xFF, and the subsequent code that finds the
 * right-most 0 bit would access the first byte beyond the bitmap.  Provided
 * we find a 0 bit before then, that won't happen.  Since tuples which have no
 * NULLs don't have a NULL bitmap, this function won't get called for that
 * case.
 */
static inline int
first_null_attr(const uint8 *bits, int natts)
{
    int         nattByte = natts >> 3;
    int         bytenum;
    int         res;
 
#ifdef USE_ASSERT_CHECKING
    int         firstnull_check = natts;
 
    /* Do it the slow way and check we get the same answer. */
    for (int i = 0; i < natts; i++)
    {
        if (att_isnull(i, bits))
        {
            firstnull_check = i;
            break;
        }
    }
#endif
 
    /* Process all bytes up to just before the byte for the natts attribute */
    for (bytenum = 0; bytenum < nattByte; bytenum++)
    {
        /* break if there's any NULL attrs (a 0 bit) */
        if (bits[bytenum] != 0xFF)
            break;
    }
 
    /*
     * Look for the highest 0-bit in the 'bytenum' element.  To do this, we
     * promote the uint8 to uint32 before performing the bitwise NOT and
     * looking for the first 1-bit.  This works even when the byte is 0xFF, as
     * the bitwise NOT of 0xFF in 32 bits is 0xFFFFFF00, in which case
     * pg_rightmost_one_pos32() will return 8.  We may end up with a value
     * higher than natts here, but we'll fix that with the Min() below.
     */
    res = bytenum << 3;
    res += pg_rightmost_one_pos32(~((uint32) bits[bytenum]));
 
    /*
     * Since we did no masking to mask out bits beyond the natts'th bit, we
     * may have found a bit higher than natts, so we must cap res to natts
     */
    res = Min(res, natts);
 
    /* Ensure we got the same answer as the att_isnull() loop got */
    Assert(res == firstnull_check);
 
    return res;
}
#endif                          /* FRONTEND */
 
/*
 * typalign_to_alignby: map a TYPALIGN_xxx value to the numeric alignment
 * value it represents.  (We store TYPALIGN_xxx codes not the real alignment
 * values mainly so that initial catalog contents can be machine-independent.)
 */
static inline uint8
typalign_to_alignby(char typalign)
{
    uint8       alignby;
 
    switch (typalign)
    {
        case TYPALIGN_CHAR:
            alignby = sizeof(char);
            break;
        case TYPALIGN_SHORT:
            alignby = ALIGNOF_SHORT;
            break;
        case TYPALIGN_INT:
            alignby = ALIGNOF_INT;
            break;
        case TYPALIGN_DOUBLE:
            alignby = ALIGNOF_DOUBLE;
            break;
        default:
#ifndef FRONTEND
            elog(ERROR, "invalid typalign value: %c", typalign);
#else
            fprintf(stderr, "invalid typalign value: %c\n", typalign);
            exit(1);
#endif
            alignby = 0;
            break;
    }
    return alignby;
}
 
/*
 * att_align_datum aligns the given offset as needed for a datum of alignment
 * requirement attalign and typlen attlen.  attdatum is the Datum variable
 * we intend to pack into a tuple (it's only accessed if we are dealing with
 * a varlena type).  Note that this assumes the Datum will be stored as-is;
 * callers that are intending to convert non-short varlena datums to short
 * format have to account for that themselves.
 */
#define att_align_datum(cur_offset, attalign, attlen, attdatum) \
( \
    ((attlen) == -1 && VARATT_IS_SHORT(DatumGetPointer(attdatum))) ? \
    (uintptr_t) (cur_offset) : \
    att_align_nominal(cur_offset, attalign) \
)
 
/*
 * Similar to att_align_datum, but accepts a number of bytes, typically from
 * CompactAttribute.attalignby to align the Datum by.
 */
#define att_datum_alignby(cur_offset, attalignby, attlen, attdatum) \
    ( \
    ((attlen) == -1 && VARATT_IS_SHORT(DatumGetPointer(attdatum))) ? \
    (uintptr_t) (cur_offset) : \
    TYPEALIGN(attalignby, cur_offset))
 
/*
 * att_align_pointer performs the same calculation as att_align_datum,
 * but is used when walking a tuple.  attptr is the current actual data
 * pointer; when accessing a varlena field we have to "peek" to see if we
 * are looking at a pad byte or the first byte of a 1-byte-header datum.
 * (A zero byte must be either a pad byte, or the first byte of a correctly
 * aligned 4-byte length word; in either case we can align safely.  A non-zero
 * byte must be either a 1-byte length word, or the first byte of a correctly
 * aligned 4-byte length word; in either case we need not align.)
 *
 * Note: some callers pass a "char *" pointer for cur_offset.  This is
 * a bit of a hack but should work all right as long as uintptr_t is the
 * correct width.
 */
#define att_align_pointer(cur_offset, attalign, attlen, attptr) \
( \
    ((attlen) == -1 && VARATT_NOT_PAD_BYTE(attptr)) ? \
    (uintptr_t) (cur_offset) : \
    att_align_nominal(cur_offset, attalign) \
)
 
/*
 * Similar to att_align_pointer, but accepts a number of bytes, typically from
 * CompactAttribute.attalignby to align the pointer by.
 */
#define att_pointer_alignby(cur_offset, attalignby, attlen, attptr) \
    ( \
    ((attlen) == -1 && VARATT_NOT_PAD_BYTE(attptr)) ? \
    (uintptr_t) (cur_offset) : \
    TYPEALIGN(attalignby, cur_offset))
 
/*
 * att_align_nominal aligns the given offset as needed for a datum of alignment
 * requirement attalign, ignoring any consideration of packed varlena datums.
 * There are three main use cases for using this macro directly:
 *  * we know that the att in question is not varlena (attlen != -1);
 *    in this case it is cheaper than the above macros and just as good.
 *  * we need to estimate alignment padding cost abstractly, ie without
 *    reference to a real tuple.  We must assume the worst case that
 *    all varlenas are aligned.
 *  * within arrays and multiranges, we unconditionally align varlenas (XXX this
 *    should be revisited, probably).
 *
 * In performance-critical loops, avoid using this macro; instead use
 * att_nominal_alignby with a pre-computed alignby value.
 */
#define att_align_nominal(cur_offset, attalign) \
    att_nominal_alignby(cur_offset, typalign_to_alignby(attalign))
 
/*
 * Similar to att_align_nominal, but accepts a number of bytes, typically from
 * CompactAttribute.attalignby to align the offset by.
 */
#define att_nominal_alignby(cur_offset, attalignby) \
    TYPEALIGN(attalignby, cur_offset)
 
/*
 * att_addlength_datum increments the given offset by the space needed for
 * the given Datum variable.  attdatum is only accessed if we are dealing
 * with a variable-length attribute.
 */
#define att_addlength_datum(cur_offset, attlen, attdatum) \
    att_addlength_pointer(cur_offset, attlen, DatumGetPointer(attdatum))
 
/*
 * att_addlength_pointer performs the same calculation as att_addlength_datum,
 * but is used when walking a tuple --- attptr is the pointer to the field
 * within the tuple.
 *
 * Note: some callers pass a "char *" pointer for cur_offset.  This is
 * actually perfectly OK, but probably should be cleaned up along with
 * the same practice for att_align_pointer.
 */
#define att_addlength_pointer(cur_offset, attlen, attptr) \
( \
    ((attlen) > 0) ? \
    ( \
        (cur_offset) + (attlen) \
    ) \
    : (((attlen) == -1) ? \
    ( \
        (cur_offset) + VARSIZE_ANY(attptr) \
    ) \
    : \
    ( \
        AssertMacro((attlen) == -2), \
        (cur_offset) + (strlen((const char *) (attptr)) + 1) \
    )) \
)
 
#ifndef FRONTEND
/*
 * store_att_byval is a partial inverse of fetch_att: store a given Datum
 * value into a tuple data area at the specified address.  However, it only
 * handles the byval case, because in typical usage the caller needs to
 * distinguish by-val and by-ref cases anyway, and so a do-it-all function
 * wouldn't be convenient.
 */
static inline void
store_att_byval(void *T, Datum newdatum, int attlen)
{
    switch (attlen)
    {
        case sizeof(char):
            *(char *) T = DatumGetChar(newdatum);
            break;
        case sizeof(int16):
            *(int16 *) T = DatumGetInt16(newdatum);
            break;
        case sizeof(int32):
            *(int32 *) T = DatumGetInt32(newdatum);
            break;
        case sizeof(int64):
            *(int64 *) T = DatumGetInt64(newdatum);
            break;
        default:
            elog(ERROR, "unsupported byval length: %d", attlen);
    }
}
#endif                          /* FRONTEND */
 
#endif                          /* TUPMACS_H */