Fixing Math.pow

The Math.pow implementation relies on libm's pow. However, the ISO C
and ES5.1 standards differ on pow:
  * `x ** NAN` is NAN in ES but `+1 ** y` is 1 in C
  * `+-1 ** +-INF` is NAN in ES but 1 in C

This patch:
  * Modifies the Math.pow implementation to handle the special cases
    instead calling pow.
  * Adds a test case to jerry-test-suite as it did not test
    `Math.pow(1,NaN)`.
  * Fixes jerry-libm's pow, as it was not standard conforming, which
    helped hiding the error in Math.pow.
  * Updates the unit test for libm.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss [email protected]

Author: akosthekiss

jerry-core/ecma/builtin-objects/ecma-builtin-math.c

@@ -477,7 +477,16 @@ ecma_builtin_math_object_pow (ecma_value_t this_arg, /**< 'this' argument */
   ECMA_OP_TO_NUMBER_TRY_CATCH (x, arg1, ret_value);
   ECMA_OP_TO_NUMBER_TRY_CATCH (y, arg2, ret_value);
 
-  ret_value = ecma_make_number_value (DOUBLE_TO_ECMA_NUMBER_T (pow (x, y)));
+  if (ecma_number_is_nan (y) ||
+      (ecma_number_is_infinity (y) && (x == 1.0 || x == -1.0)))
+  {
+    /* Handle differences between ES5.1 and ISO C standards for pow. */
+    ret_value = ecma_make_number_value (ecma_number_make_nan ());
+  }
+  else
+  {
+    ret_value = ecma_make_number_value (DOUBLE_TO_ECMA_NUMBER_T (pow (x, y)));
+  }
 
   ECMA_OP_TO_NUMBER_FINALIZE (y);
   ECMA_OP_TO_NUMBER_FINALIZE (x);

jerry-libm/pow.c

@@ -39,6 +39,7 @@
  *      3. Return x**y = 2**n*exp(y'*log2)
  *
  * Special cases:
+ *      0.  +1 ** (anything) is 1
  *      1.  (anything) ** 0  is 1
  *      2.  (anything) ** 1  is itself
  *      3.  (anything) ** NAN is NAN
@@ -47,7 +48,7 @@
  *      6.  +-(|x| > 1) **  -INF is +0
  *      7.  +-(|x| < 1) **  +INF is +0
  *      8.  +-(|x| < 1) **  -INF is +INF
- *      9.  +-1         ** +-INF is NAN
+ *      9.  -1          ** +-INF is 1
  *      10. +0 ** (+anything except 0, NAN)               is +0
  *      11. -0 ** (+anything except 0, NAN, odd integer)  is +0
  *      12. +0 ** (-anything except 0, NAN)               is +INF
@@ -133,6 +134,12 @@ pow (double x, double y)
   ix = hx & 0x7fffffff;
   iy = hy & 0x7fffffff;
 
+  /* x == one: 1**y = 1 */
+  if (((hx - 0x3ff00000) | lx) == 0)
+  {
+    return one;
+  }
+
   /* y == zero: x**0 = 1 */
   if ((iy | ly) == 0)
   {
@@ -184,9 +191,9 @@ pow (double x, double y)
   {
     if (iy == 0x7ff00000) /* y is +-inf */
     {
-      if (((ix - 0x3ff00000) | lx) == 0) /* inf**+-1 is NaN */
+      if (((ix - 0x3ff00000) | lx) == 0) /* +-1**+-inf is 1 */
       {
-        return y - y;
+        return one;
       }
       else if (ix >= 0x3ff00000) /* (|x|>1)**+-inf = inf,0 */
       {

tests/jerry-test-suite/15/15.08/15.08.02/15.08.02.13/15.08.02.13-031.js

@@ -0,0 +1,16 @@
+// Copyright 2016 Samsung Electronics Co., Ltd.
+// Copyright 2016 University of Szeged
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+assert(isNaN(Math.pow(1, NaN)));

tests/unit/test-libm.inc.h

@@ -330,6 +330,11 @@ check_double ("pow (1.0, 1.0)", pow (1.0, 1.0), 1.00000000000000000000E+00);
 check_double ("pow (1.0, -1.0)", pow (1.0, -1.0), 1.00000000000000000000E+00);
 check_double ("pow (-1.0, 1.0)", pow (-1.0, 1.0), -1.00000000000000000000E+00);
 check_double ("pow (-1.0, -1.0)", pow (-1.0, -1.0), -1.00000000000000000000E+00);
+check_double ("pow (1.0, INFINITY)", pow (1.0, INFINITY), 1.00000000000000000000E+00);
+check_double ("pow (1.0, -INFINITY)", pow (1.0, -INFINITY), 1.00000000000000000000E+00);
+check_double ("pow (-1.0, INFINITY)", pow (-1.0, INFINITY), 1.00000000000000000000E+00);
+check_double ("pow (-1.0, -INFINITY)", pow (-1.0, -INFINITY), 1.00000000000000000000E+00);
+check_double ("pow (1.0, NAN)", pow (1.0, NAN), 1.00000000000000000000E+00);
 check_double ("pow (-1.0, NAN)", pow (-1.0, NAN), NAN);
 check_double ("pow (INFINITY, 0.0)", pow (INFINITY, 0.0), 1.00000000000000000000E+00);
 check_double ("pow (INFINITY, -0.0)", pow (INFINITY, -0.0), 1.00000000000000000000E+00);

tools/unit-tests/gen-test-libm.c

@@ -465,13 +465,11 @@ main (int argc, char **args)
   GEN_DBL_TEST (pow (1.0, -1.0));
   GEN_DBL_TEST (pow (-1.0, 1.0));
   GEN_DBL_TEST (pow (-1.0, -1.0));
-  /* SKIPPED: reference libm implementation seems to (incorrectly?) result 1.0 instead of NAN
   GEN_DBL_TEST (pow (1.0, INFINITY));
   GEN_DBL_TEST (pow (1.0, -INFINITY));
   GEN_DBL_TEST (pow (-1.0, INFINITY));
   GEN_DBL_TEST (pow (-1.0, -INFINITY));
   GEN_DBL_TEST (pow (1.0, NAN));
-  */
   GEN_DBL_TEST (pow (-1.0, NAN));
   GEN_DBL_TEST (pow (INFINITY, 0.0));
   GEN_DBL_TEST (pow (INFINITY, -0.0));