Avoid wrong results for power() with NaN input on more platforms.

Buildfarm results show that the modern POSIX rule that 1 ^ NaN = 1 is not
honored on *BSD until relatively recently, and really old platforms don't
believe that NaN ^ 0 = 1 either.  (This is unsurprising, perhaps, since
SUSv2 doesn't require either behavior.)  In hopes of getting to platform
independent behavior, let's deal with all the NaN-input cases explicitly
in dpow().

Note that numeric_power() doesn't know either of these special cases.
But since that behavior is platform-independent, I think it should be
addressed separately, and probably not back-patched.

Discussion: https://postgr.es/m/75DB81BEEA95B445AE6D576A0A5C9E936A73E741@BPXM05GP.gisp.nec.co.jp

diff --git a/src/backend/utils/adt/float.c b/src/backend/utils/adt/float.c
index 9f4afaa08b9e60de98ca8a10a61ab22c0ef57750..45a62f261615d9c88e97b1a72f10b97ac5bb224e 100644 (file)
--- a/src/backend/utils/adt/float.c
+++ b/src/backend/utils/adt/float.c
@@ -1461,6 +1461,25 @@ dpow(PG_FUNCTION_ARGS)
        float8          arg2 = PG_GETARG_FLOAT8(1);
        float8          result;
 
+       /*
+        * The POSIX spec says that NaN ^ 0 = 1, and 1 ^ NaN = 1, while all other
+        * cases with NaN inputs yield NaN (with no error).  Many older platforms
+        * get one or more of these cases wrong, so deal with them via explicit
+        * logic rather than trusting pow(3).
+        */
+       if (isnan(arg1))
+       {
+               if (isnan(arg2) || arg2 != 0.0)
+                       PG_RETURN_FLOAT8(get_float8_nan());
+               PG_RETURN_FLOAT8(1.0);
+       }
+       if (isnan(arg2))
+       {
+               if (arg1 != 1.0)
+                       PG_RETURN_FLOAT8(get_float8_nan());
+               PG_RETURN_FLOAT8(1.0);
+       }
+
        /*
         * The SQL spec requires that we emit a particular SQLSTATE error code for
         * certain error conditions.  Specifically, we don't return a
@@ -1482,12 +1501,11 @@ dpow(PG_FUNCTION_ARGS)
         * and result == NaN for negative arg1 and very large arg2 (they must be
         * using something different from our floor() test to decide it's
         * invalid).  Other platforms (HPPA) return errno == ERANGE and a large
-        * (HUGE_VAL) but finite result to signal overflow.  Also, some versions
-        * of MSVC return errno == EDOM and result == NaN for NaN inputs.
+        * (HUGE_VAL) but finite result to signal overflow.
         */
        errno = 0;
        result = pow(arg1, arg2);
-       if (errno == EDOM && isnan(result) && !isnan(arg1) && !isnan(arg2))
+       if (errno == EDOM && isnan(result))
        {
                if ((fabs(arg1) > 1 && arg2 >= 0) || (fabs(arg1) < 1 && arg2 < 0))
                        /* The sign of Inf is not significant in this case. */

diff --git a/src/test/regress/expected/float8-exp-three-digits-win32.out b/src/test/regress/expected/float8-exp-three-digits-win32.out
index 3fe50b4bf008ee7478a9698a73be7f22b2cfb9c2..3896cdec7216296b19a796884f6242d8b6499219 100644 (file)
--- a/src/test/regress/expected/float8-exp-three-digits-win32.out
+++ b/src/test/regress/expected/float8-exp-three-digits-win32.out
@@ -358,6 +358,12 @@ SELECT power(float8 'NaN', float8 'NaN');
    NaN
 (1 row)
 
+SELECT power(float8 '-1', float8 'NaN');
+ power 
+-------
+   NaN
+(1 row)
+
 SELECT power(float8 '1', float8 'NaN');
  power 
 -------

diff --git a/src/test/regress/expected/float8-small-is-zero.out b/src/test/regress/expected/float8-small-is-zero.out
index 46adbe1c4ba9a35be65b47c72247486f11f18013..f8e09390f518c054569594db469e110788de2d6d 100644 (file)
--- a/src/test/regress/expected/float8-small-is-zero.out
+++ b/src/test/regress/expected/float8-small-is-zero.out
@@ -362,6 +362,12 @@ SELECT power(float8 'NaN', float8 'NaN');
    NaN
 (1 row)
 
+SELECT power(float8 '-1', float8 'NaN');
+ power 
+-------
+   NaN
+(1 row)
+
 SELECT power(float8 '1', float8 'NaN');
  power 
 -------

diff --git a/src/test/regress/expected/float8-small-is-zero_1.out b/src/test/regress/expected/float8-small-is-zero_1.out
index f215eede103817684cb856c5a189aa362a5a3569..ebfec4cdb6899ba5a53834751c014e999a5dafee 100644 (file)
--- a/src/test/regress/expected/float8-small-is-zero_1.out
+++ b/src/test/regress/expected/float8-small-is-zero_1.out
@@ -362,6 +362,12 @@ SELECT power(float8 'NaN', float8 'NaN');
    NaN
 (1 row)
 
+SELECT power(float8 '-1', float8 'NaN');
+ power 
+-------
+   NaN
+(1 row)
+
 SELECT power(float8 '1', float8 'NaN');
  power 
 -------

diff --git a/src/test/regress/expected/float8.out b/src/test/regress/expected/float8.out
index 7159e78d4a7d440c28398b794a42f61b56772042..b05831d45c954918bc65f0f168fb6f711a6fd4d9 100644 (file)
--- a/src/test/regress/expected/float8.out
+++ b/src/test/regress/expected/float8.out
@@ -358,6 +358,12 @@ SELECT power(float8 'NaN', float8 'NaN');
    NaN
 (1 row)
 
+SELECT power(float8 '-1', float8 'NaN');
+ power 
+-------
+   NaN
+(1 row)
+
 SELECT power(float8 '1', float8 'NaN');
  power 
 -------

diff --git a/src/test/regress/sql/float8.sql b/src/test/regress/sql/float8.sql
index 5510fe9d3456cd171e9b24439b26c18322e718ad..eeebddd4b78d334ee73a777403b55060475c101a 100644 (file)
--- a/src/test/regress/sql/float8.sql
+++ b/src/test/regress/sql/float8.sql
@@ -111,6 +111,7 @@ SELECT power(float8 '144', float8 '0.5');
 SELECT power(float8 'NaN', float8 '0.5');
 SELECT power(float8 '144', float8 'NaN');
 SELECT power(float8 'NaN', float8 'NaN');
+SELECT power(float8 '-1', float8 'NaN');
 SELECT power(float8 '1', float8 'NaN');
 SELECT power(float8 'NaN', float8 '0');