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

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

diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
index 7e47aa038e0ee8d97d8708683b818e724a92de9d..d5d2b1cfad0bfc50c7f5cecf5db11e6e28896f77 100644 (file)
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -205,6 +205,7 @@ struct NumericData
  */
 
 #define NUMERIC_DSCALE_MASK            0x3FFF
+#define NUMERIC_DSCALE_MAX         NUMERIC_DSCALE_MASK
 
 #define NUMERIC_SIGN(n) \
    (NUMERIC_IS_SHORT(n) ? \
@@ -2549,7 +2550,11 @@ numeric_mul_opt_error(Numeric num1, Numeric num2, bool *have_error)
     * 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);
@@ -2557,6 +2562,9 @@ numeric_mul_opt_error(Numeric num1, Numeric num2, bool *have_error)
    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_opt_error(&result, have_error);
 
    free_var(&result);

diff --git a/src/test/regress/expected/numeric.out b/src/test/regress/expected/numeric.out
index c05bf7b8e6a6f680fe5bc7a7861793033c9ff3cc..dbb9e4ad1f152c0c96a1dc1f8a978bf1652a95b6 100644 (file)
--- a/src/test/regress/expected/numeric.out
+++ b/src/test/regress/expected/numeric.out
@@ -1498,6 +1498,12 @@ select 4769999999999999999999999999999999999999999999999999999999999999999999999
  47699999999999999999999999999999999999999999999999999999999999999999999999999999999999985230000000000000000000000000000000000000000000000000000000000000000000000000000000000001
 (1 row)
 
+select trim_scale((0.1 - 2e-16383) * (0.1 - 3e-16383));
+ trim_scale 
+------------
+       0.01
+(1 row)
+
 --
 -- Test some corner cases for division
 --

diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sql
index 6fa8d3fcc0b06e1b64e0e218c30dd43aa053d407..3d03862b6461a34116b8bef87e0ff9c24179af0f 100644 (file)
--- a/src/test/regress/sql/numeric.sql
+++ b/src/test/regress/sql/numeric.sql
@@ -864,6 +864,8 @@ select 4770999999999999999999999999999999999999999999999999999999999999999999999
 
 select 4769999999999999999999999999999999999999999999999999999999999999999999999999999999999999 * 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999;
 
+select trim_scale((0.1 - 2e-16383) * (0.1 - 3e-16383));
+
 --
 -- Test some corner cases for division
 --