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Fix numeric_mul() overflow due to too many digits after decimal point.

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This fixes an overflow error when using the numeric * operator if the
result has more than 16383 digits after the decimal point by rounding
the result. Overflow errors should only occur if the result has too
many digits *before* the decimal point.

Discussion: https://postgr.es/m/CAEZATCUmeFWCrq2dNzZpRj5+6LfN85jYiDoqm+ucSXhb9U2TbA@mail.gmail.com
This commit is contained in:
Dean Rasheed 2021-07-10 12:50:05 +01:00
parent 56533fce73
commit 54a0ec1bd6
3 changed files with 17 additions and 1 deletions
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10
src/backend/utils/adt/numeric.c
View File

@ -202,6 +202,7 @@ struct NumericData
*/
#define NUMERIC_DSCALE_MASK 0x3FFF
#define NUMERIC_DSCALE_MAX NUMERIC_DSCALE_MASK
#define NUMERIC_SIGN(n) \
(NUMERIC_IS_SHORT(n) ? \
@ -2341,7 +2342,11 @@ numeric_mul(PG_FUNCTION_ARGS)
* Unlike add_var() and sub_var(), mul_var() will round its result. In the
* case of numeric_mul(), which is invoked for the * operator on numerics,
* we request exact representation for the product (rscale = sum(dscale of
* arg1, dscale of arg2)).
* arg1, dscale of arg2)). If the exact result has more digits after the
* decimal point than can be stored in a numeric, we round it. Rounding
* after computing the exact result ensures that the final result is
* correctly rounded (rounding in mul_var() using a truncated product
* would not guarantee this).
*/
init_var_from_num(num1, &arg1);
init_var_from_num(num2, &arg2);
@ -2349,6 +2354,9 @@ numeric_mul(PG_FUNCTION_ARGS)
init_var(&result);
mul_var(&arg1, &arg2, &result, arg1.dscale + arg2.dscale);
if (result.dscale > NUMERIC_DSCALE_MAX)
round_var(&result, NUMERIC_DSCALE_MAX);
res = make_result(&result);
free_var(&result);

6
src/test/regress/expected/numeric.out
View File

@ -1381,6 +1381,12 @@ select 4769999999999999999999999999999999999999999999999999999999999999999999999
47699999999999999999999999999999999999999999999999999999999999999999999999999999999999985230000000000000000000000000000000000000000000000000000000000000000000000000000000000001
(1 row)
select (0.1 - 2e-16383) * (0.1 - 3e-16383) = 0.01 as rounds_to_point_zero_one;
rounds_to_point_zero_one
--------------------------
t
(1 row)
--
-- Test some corner cases for division
--

2
src/test/regress/sql/numeric.sql
View File

@ -841,6 +841,8 @@ select 4770999999999999999999999999999999999999999999999999999999999999999999999
select 4769999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
select (0.1 - 2e-16383) * (0.1 - 3e-16383) = 0.01 as rounds_to_point_zero_one;
--
-- Test some corner cases for division
--