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/* Test of modf*() function family.
   Copyright (C) 2012-2025 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;
  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));

  /* Randomized tests.  */
  for (i = 0; i < SIZEOF (RANDOM); i++)
    {
      DOUBLE x = RANDOM[i]; /* 0.0 <= x < 1.0 */
      DOUBLE y;
      DOUBLE z;

      y = MODF (x, &z);
      ASSERT (z == L_(0.0));
      ASSERT (y == x);

      y = MODF (- x, &z);
      ASSERT (z == L_(0.0));
      ASSERT (y == - x);

      y = MODF (L_(1.0) + x, &z);
      ASSERT (z == L_(1.0));
      y -= x;
      ASSERT (y >= - L_(1.0) / TWO_MANT_DIG);
      ASSERT (y <= L_(1.0) / TWO_MANT_DIG);

      y = MODF (- L_(1.0) - x, &z);
      ASSERT (z == - L_(1.0));
      y -= - x;
      ASSERT (y >= - L_(1.0) / TWO_MANT_DIG);
      ASSERT (y <= L_(1.0) / TWO_MANT_DIG);
    }
}

volatile DOUBLE x;
DOUBLE y;
DOUBLE z;
kc3-lang/gnulib/tests/test-modf.h

Commit

tests/test-modf.h
