Numeric x^y is supported for x < 0 if y is an integer, but this
currently fails if y is outside the range of an int32:
SELECT (-1.0) ^ 2147483647;
?column?
---------------------
-1.0000000000000000
(1 row)
SELECT (-1.0) ^ 2147483648;
ERROR: cannot take logarithm of a negative number
because only the power_var_int() code path in power_var() handles
negative bases correctly. Attached is a patch to fix that.
Regards,
Dean
diff --git a/src/backend/utils/adt/numeric.c b/src/backend/utils/adt/numeric.c
new file mode 100644
index eb78f0b..3eb0d90
--- a/src/backend/utils/adt/numeric.c
+++ b/src/backend/utils/adt/numeric.c
@@ -3934,11 +3934,6 @@ numeric_power(PG_FUNCTION_ARGS)
(errcode(ERRCODE_INVALID_ARGUMENT_FOR_POWER_FUNCTION),
errmsg("zero raised to a negative power is undefined")));
- if (sign1 < 0 && !numeric_is_integral(num2))
- ereport(ERROR,
- (errcode(ERRCODE_INVALID_ARGUMENT_FOR_POWER_FUNCTION),
- errmsg("a negative number raised to a non-integer power yields a complex result")));
-
/*
* Initialize things
*/
@@ -10138,6 +10133,8 @@ log_var(const NumericVar *base, const Nu
static void
power_var(const NumericVar *base, const NumericVar *exp, NumericVar *result)
{
+ int res_sign;
+ NumericVar abs_base;
NumericVar ln_base;
NumericVar ln_num;
int ln_dweight;
@@ -10181,9 +10178,37 @@ power_var(const NumericVar *base, const
return;
}
+ init_var(&abs_base);
init_var(&ln_base);
init_var(&ln_num);
+ /*
+ * If base is negative, insist that exp be an integer. The result is then
+ * positive if exp is even and negative if exp is odd.
+ */
+ if (base->sign == NUMERIC_NEG)
+ {
+ /* digits after the decimal point? */
+ if (exp->ndigits > 0 && exp->ndigits > exp->weight + 1)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_ARGUMENT_FOR_POWER_FUNCTION),
+ errmsg("a negative number raised to a non-integer power yields a complex result")));
+
+ /* odd exponent? */
+ if (exp->ndigits > 0 && exp->ndigits == exp->weight + 1 &&
+ (exp->digits[exp->ndigits - 1] & 1))
+ res_sign = NUMERIC_NEG;
+ else
+ res_sign = NUMERIC_POS;
+
+ /* work with abs(base) */
+ set_var_from_var(base, &abs_base);
+ abs_base.sign = NUMERIC_POS;
+ base = &abs_base;
+ }
+ else
+ res_sign = NUMERIC_POS;
+
/*----------
* Decide on the scale for the ln() calculation. For this we need an
* estimate of the weight of the result, which we obtain by doing an
@@ -10240,9 +10265,12 @@ power_var(const NumericVar *base, const
mul_var(&ln_base, exp, &ln_num, local_rscale);
exp_var(&ln_num, result, rscale);
+ if (res_sign == NUMERIC_NEG && result->ndigits > 0)
+ result->sign = NUMERIC_NEG;
free_var(&ln_num);
free_var(&ln_base);
+ free_var(&abs_base);
}
/*
diff --git a/src/test/regress/expected/numeric.out b/src/test/regress/expected/numeric.out
new file mode 100644
index 30a5642..94bc773
--- a/src/test/regress/expected/numeric.out
+++ b/src/test/regress/expected/numeric.out
@@ -2340,6 +2340,37 @@ select 0.5678 ^ (-85);
782333637740774446257.7719390061997396
(1 row)
+-- negative base to integer powers
+select (-1.0) ^ 2147483646;
+ ?column?
+--------------------
+ 1.0000000000000000
+(1 row)
+
+select (-1.0) ^ 2147483647;
+ ?column?
+---------------------
+ -1.0000000000000000
+(1 row)
+
+select (-1.0) ^ 2147483648;
+ ?column?
+--------------------
+ 1.0000000000000000
+(1 row)
+
+select (-1.0) ^ 1000000000000000;
+ ?column?
+--------------------
+ 1.0000000000000000
+(1 row)
+
+select (-1.0) ^ 1000000000000001;
+ ?column?
+---------------------
+ -1.0000000000000000
+(1 row)
+
--
-- Tests for raising to non-integer powers
--
diff --git a/src/test/regress/sql/numeric.sql b/src/test/regress/sql/numeric.sql
new file mode 100644
index db812c8..58c1c69
--- a/src/test/regress/sql/numeric.sql
+++ b/src/test/regress/sql/numeric.sql
@@ -1095,6 +1095,13 @@ select 1.000000000123 ^ (-2147483648);
select 0.12 ^ (-25);
select 0.5678 ^ (-85);
+-- negative base to integer powers
+select (-1.0) ^ 2147483646;
+select (-1.0) ^ 2147483647;
+select (-1.0) ^ 2147483648;
+select (-1.0) ^ 1000000000000000;
+select (-1.0) ^ 1000000000000001;
+
--
-- Tests for raising to non-integer powers
--
