kc3-lang/gnulib/tests/test-log2.h

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• Hash : 32a72f45
  Author :
  Date : 2023-01-01T01:14:21
  

  maint: run 'make update-copyright'
  

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• tests/test-log2.h

• /* Test of log2*() function family.
     Copyright (C) 2012-2023 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));
  
    /* Pole.  */
    ASSERT (LOG2 (L_(0.0)) == - HUGEVAL);
    ASSERT (LOG2 (MINUS_ZERO) == - HUGEVAL);
  
    /* Integral values.  */
    {
      DOUBLE x = L_(1.0);
      DOUBLE y = LOG2 (x);
      ASSERT (y == L_(0.0));
    }
    {
      int e;
      DOUBLE x;
      DOUBLE y;
      for (e = 0, x = L_(0.0), y = L_(1.0);
           e <= MAX_EXP - 1;
           e++, x = x + L_(1.0), y = y * L_(2.0))
        {
          /* Invariant: x = e, y = 2^e.  */
          DOUBLE z = LOG2 (y);
          ASSERT (z == x);
        }
    }
    {
      int e;
      DOUBLE x;
      DOUBLE y;
      for (e = 0, x = L_(0.0), y = L_(1.0);
           e >= MIN_EXP - 1;
           e--, x = x - L_(1.0), y = y * L_(0.5))
        {
          /* Invariant: x = e, y = 2^e.  */
          DOUBLE z = LOG2 (y);
          ASSERT (z == x);
        }
    }
  
    /* Randomized tests.  */
    {
      /* Error bound, in ulps.  */
      const DOUBLE err_bound =
        (sizeof (DOUBLE) > sizeof (double) ?
  #if defined __i386__ && defined __FreeBSD__
         /* On FreeBSD/x86 6.4, the 'long double' type really has only 53 bits of
            precision in the compiler but 64 bits of precision at runtime.  See
            <https://lists.gnu.org/r/bug-gnulib/2008-07/msg00063.html>.
            The compiler has truncated all 'long double' literals in log2l.c to
            53 bits of precision.  */
         L_(8193.0)
  #else
         L_(5.0)
  #endif
         : L_(5.0));
  
      for (i = 0; i < SIZEOF (RANDOM); i++)
        {
          DOUBLE x = L_(16.0) * RANDOM[i] + L_(1.0); /* 1.0 <= x <= 17.0 */
          DOUBLE y = LOG2 (x);
          DOUBLE z = LOG2 (L_(1.0) / x);
          DOUBLE err = y + z;
          ASSERT (y >= L_(0.0));
          ASSERT (z <= L_(0.0));
          ASSERT (err > - err_bound / TWO_MANT_DIG
                  && err < err_bound / TWO_MANT_DIG);
        }
    }
  
    {
      /* Error bound, in ulps.  */
      const DOUBLE err_bound =
        (sizeof (DOUBLE) > sizeof (double) ?
  #if defined __i386__ && defined __FreeBSD__
         /* On FreeBSD/x86 6.4, the 'long double' type really has only 53 bits of
            precision in the compiler but 64 bits of precision at runtime.  See
            <https://lists.gnu.org/r/bug-gnulib/2008-07/msg00063.html>.
            The compiler has truncated all 'long double' literals in log2l.c to
            53 bits of precision.  */
         L_(8193.0)
  #else
         L_(9.0)
  #endif
         : L_(9.0));
  
      for (i = 0; i < SIZEOF (RANDOM) / 5; i++)
        for (j = 0; j < SIZEOF (RANDOM) / 5; j++)
          {
            DOUBLE x = L_(17.0) / (L_(16.0) - L_(15.0) * RANDOM[i]) - L_(1.0);
            DOUBLE y = L_(17.0) / (L_(16.0) - L_(15.0) * RANDOM[j]) - L_(1.0);
            /* 1/16 <= x,y <= 16 */
            DOUBLE z = L_(1.0) / (x * y);
            /* Approximately  x * y * z = 1.  */
            DOUBLE err = LOG2 (x) + LOG2 (y) + LOG2 (z);
            ASSERT (err > - err_bound / TWO_MANT_DIG
                    && err < err_bound / TWO_MANT_DIG);
          }
    }
  }
  
  volatile DOUBLE x;
  DOUBLE y;
  

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