gnulib/tests/test-hypot.h

/* Test of hypot*() function family.
   Copyright (C) 2012-2020 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

static void
test_function (void)
{
  int i;
  int j;
  const DOUBLE TWO_MANT_DIG =
    /* Assume MANT_DIG <= 5 * 31.
       Use the identity
         n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
    (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
    * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
    * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
    * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
    * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));

  {
    volatile DOUBLE x;
    volatile DOUBLE y;
    volatile DOUBLE z;

    /* Overflow.  */
    x = MAX;
    y = MAX * L_(0.5);
    z = HYPOT (x, y);
    ASSERT (z == HUGEVAL);

    /* No underflow.  */
    x = MIN;
    y = L_(0.0);
    z = HYPOT (x, y);
    ASSERT (z == MIN);

    /* No underflow.  */
    x = MIN * L_(2.0);
    y = MIN * L_(3.0);
    z = HYPOT (x, y);
    ASSERT (z >= MIN * L_(2.0) && z <= MIN * L_(4.0));
  }

  /* Randomized tests.  */
  for (i = 0; i < SIZEOF (RANDOM) / 5; i++)
    for (j = 0; j < SIZEOF (RANDOM) / 5;j++)
      {
        DOUBLE x = L_(16.0) * RANDOM[i]; /* 0.0 <= x <= 16.0 */
        DOUBLE y = L_(16.0) * RANDOM[j]; /* 0.0 <= y <= 16.0 */
        DOUBLE z = HYPOT (x, y);
        DOUBLE err = z * z - (x * x + y * y);
        ASSERT (z >= L_(0.0));
        ASSERT (err >= - L_(4.0) * L_(16.0) * L_(16.0) / TWO_MANT_DIG
                && err <= L_(4.0) * L_(16.0) * L_(16.0) / TWO_MANT_DIG);
      }
}

volatile DOUBLE x;
volatile DOUBLE y;
DOUBLE z;