diff options
Diffstat (limited to 'src/backend/utils/adt/numeric.c')
| -rw-r--r-- | src/backend/utils/adt/numeric.c | 31 |
1 files changed, 25 insertions, 6 deletions
diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c index 8398bb90e4f..0b2a1b16737 100644 --- a/src/backend/utils/adt/numeric.c +++ b/src/backend/utils/adt/numeric.c @@ -14,7 +14,7 @@ * Copyright (c) 1998-2010, PostgreSQL Global Development Group * * 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. */ int32 -numeric_maximum_size(int32 typemod) +numeric_maximum_size(int32 typmod) { int precision; + int numeric_digits; - if (typemod <= VARHDRSZ) + if (typmod < (int32) (VARHDRSZ)) return -1; /* precision (ie, max # of digits) is in upper bits of typmod */ - precision = ((typemod - VARHDRSZ) >> 16) & 0xffff; + precision = ((typmod - VARHDRSZ) >> 16) & 0xffff; + + /* + * 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; - /* Numeric stores 2 decimal digits/byte, plus header */ - return (precision + 1) / 2 + NUMERIC_HDRSZ; + /* + * 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)); } /* |