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Fix numeric_maximum_size() calculation.

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The old computation can sometimes underestimate the necessary space
by 2 bytes; however we're not back-patching this, because this result
isn't used for anything critical.  Per discussion with Tom Lane,
make the typmod test in this function match the ones in numeric()
and apply_typmod() exactly.
This commit is contained in:
Robert Haas
2010-08-04 17:33:09 +00:00
parent ba19b23676
commit 97f38001ac
1 changed files with 25 additions and 6 deletions
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31
src/backend/utils/adt/numeric.c
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@ -14,7 +14,7 @@
* Copyright (c) 1998-2010, PostgreSQL Global Development Group * Copyright (c) 1998-2010, PostgreSQL Global Development Group
* *
* IDENTIFICATION * IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/adt/numeric.c,v 1.125 2010/08/03 23:09:29 rhaas Exp $ * $PostgreSQL: pgsql/src/backend/utils/adt/numeric.c,v 1.126 2010/08/04 17:33:09 rhaas Exp $
* *
*------------------------------------------------------------------------- *-------------------------------------------------------------------------
*/ */
@ -565,18 +565,37 @@ numeric_is_nan(Numeric num)
* Maximum size of a numeric with given typmod, or -1 if unlimited/unknown. * Maximum size of a numeric with given typmod, or -1 if unlimited/unknown.
*/ */
int32 int32
numeric_maximum_size(int32 typemod) numeric_maximum_size(int32 typmod)
{ {
int precision; int precision;
int numeric_digits;
if (typemod <= VARHDRSZ) if (typmod < (int32) (VARHDRSZ))
return -1; return -1;
/* precision (ie, max # of digits) is in upper bits of typmod */ /* precision (ie, max # of digits) is in upper bits of typmod */
precision = ((typemod - VARHDRSZ) >> 16) & 0xffff; precision = ((typmod - VARHDRSZ) >> 16) & 0xffff;
/* Numeric stores 2 decimal digits/byte, plus header */ /*
return (precision + 1) / 2 + NUMERIC_HDRSZ; * This formula computes the maximum number of NumericDigits we could
* need in order to store the specified number of decimal digits.
* Because the weight is stored as a number of NumericDigits rather
* than a number of decimal digits, it's possible that the first
* NumericDigit will contain only a single decimal digit. Thus, the
* first two decimal digits can require two NumericDigits to store,
* but it isn't until we reach DEC_DIGITS + 2 decimal digits that we
* potentially need a third NumericDigit.
*/
numeric_digits = (precision + 2 * (DEC_DIGITS - 1)) / DEC_DIGITS;
/*
* In most cases, the size of a numeric will be smaller than the value
* computed below, because the varlena header will typically get toasted
* down to a single byte before being stored on disk, and it may also
* be possible to use a short numeric header. But our job here is to
* compute the worst case.
*/
return NUMERIC_HDRSZ + (numeric_digits * sizeof(NumericDigit));
} }
/* /*