tests/test-cbrt.h

   1 /* Test of cbrt*() function family.
   2    Copyright (C) 2012-2024 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 static void
  18 test_function (void)
  19 {
  20   int i;
  21   int j;
  22   const DOUBLE TWO_MANT_DIG =
  23     /* Assume MANT_DIG <= 5 * 31.
  24        Use the identity
  25          n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
  26     (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
  27     * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
  28     * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
  29     * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
  30     * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
  31
  32   /* Randomized tests.  */
  33   for (i = 0; i < SIZEOF (RANDOM); i++)
  34     {
  35       DOUBLE x = L_(32.0) * RANDOM[i] - L_(16.0); /* -16.0 <= x <= 16.0 */
  36       DOUBLE y = CBRT (x);
  37       DOUBLE err = y * y * y - x;
  38       ASSERT (err > - L_(4.0) * L_(16.0) / TWO_MANT_DIG
  39               && err < L_(4.0) * L_(16.0) / TWO_MANT_DIG);
  40     }
  41
  42   for (i = 0; i < SIZEOF (RANDOM) / 5; i++)
  43     for (j = 0; j < SIZEOF (RANDOM) / 5; j++)
  44       {
  45         DOUBLE x = L_(32.0) * RANDOM[i] - L_(16.0); /* -16.0 <= x <= 16.0 */
  46         DOUBLE y = L_(32.0) * RANDOM[j] - L_(16.0); /* -16.0 <= y <= 16.0 */
  47         if (x != L_(0.0) && y != L_(0.0))
  48           {
  49             DOUBLE z = L_(1.0) / (x * y);
  50             /* Approximately  x * y * z = 1.  */
  51             DOUBLE p = CBRT (x) * CBRT (y) * CBRT (z);
  52             ASSERT (p > L_(1.0) - L_(8.0) / TWO_MANT_DIG
  53                     && p < L_(1.0) + L_(8.0) / TWO_MANT_DIG);
  54           }
  55       }
  56 }
  57
  58 volatile DOUBLE x;
  59 DOUBLE y;