tests/test-printf-frexp.c

   1 /* Test of splitting a double into fraction and mantissa.
   2    Copyright (C) 2007-2024 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 /* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
  18
  19 #include <config.h>
  20
  21 #include "printf-frexp.h"
  22
  23 #include <float.h>
  24
  25 #include "macros.h"
  26
  27 static double
  28 my_ldexp (double x, int d)
  29 {
  30   for (; d > 0; d--)
  31     x *= 2.0;
  32   for (; d < 0; d++)
  33     x *= 0.5;
  34   return x;
  35 }
  36
  37 int
  38 main ()
  39 {
  40   int i;
  41   /* The use of 'volatile' guarantees that excess precision bits are dropped
  42      when dealing with denormalized numbers.  It is necessary on x86 systems
  43      where double-floats are not IEEE compliant by default, to avoid that the
  44      results become platform and compiler option dependent.  'volatile' is a
  45      portable alternative to gcc's -ffloat-store option.  */
  46   volatile double x;
  47
  48   for (i = 1, x = 1.0; i <= DBL_MAX_EXP; i++, x *= 2.0)
  49     {
  50       int exp = -9999;
  51       double mantissa = printf_frexp (x, &exp);
  52       ASSERT (exp == i - 1);
  53       ASSERT (mantissa == 1.0);
  54     }
  55   for (i = 1, x = 1.0; i >= DBL_MIN_EXP; i--, x *= 0.5)
  56     {
  57       int exp = -9999;
  58       double mantissa = printf_frexp (x, &exp);
  59       ASSERT (exp == i - 1);
  60       ASSERT (mantissa == 1.0);
  61     }
  62   for (; i >= DBL_MIN_EXP - 100 && x > 0.0; i--, x *= 0.5)
  63     {
  64       int exp = -9999;
  65       double mantissa = printf_frexp (x, &exp);
  66       ASSERT (exp == DBL_MIN_EXP - 1);
  67       ASSERT (mantissa == my_ldexp (1.0, i - DBL_MIN_EXP));
  68     }
  69
  70   for (i = 1, x = 1.01; i <= DBL_MAX_EXP; i++, x *= 2.0)
  71     {
  72       int exp = -9999;
  73       double mantissa = printf_frexp (x, &exp);
  74       ASSERT (exp == i - 1);
  75       ASSERT (mantissa == 1.01);
  76     }
  77   for (i = 1, x = 1.01; i >= DBL_MIN_EXP; i--, x *= 0.5)
  78     {
  79       int exp = -9999;
  80       double mantissa = printf_frexp (x, &exp);
  81       ASSERT (exp == i - 1);
  82       ASSERT (mantissa == 1.01);
  83     }
  84   for (; i >= DBL_MIN_EXP - 100 && x > 0.0; i--, x *= 0.5)
  85     {
  86       int exp = -9999;
  87       double mantissa = printf_frexp (x, &exp);
  88       ASSERT (exp == DBL_MIN_EXP - 1);
  89       ASSERT (mantissa >= my_ldexp (1.0, i - DBL_MIN_EXP));
  90       ASSERT (mantissa <= my_ldexp (2.0, i - DBL_MIN_EXP));
  91       ASSERT (mantissa == my_ldexp (x, - exp));
  92     }
  93
  94   for (i = 1, x = 1.73205; i <= DBL_MAX_EXP; i++, x *= 2.0)
  95     {
  96       int exp = -9999;
  97       double mantissa = printf_frexp (x, &exp);
  98       ASSERT (exp == i - 1);
  99       ASSERT (mantissa == 1.73205);
 100     }
 101   for (i = 1, x = 1.73205; i >= DBL_MIN_EXP; i--, x *= 0.5)
 102     {
 103       int exp = -9999;
 104       double mantissa = printf_frexp (x, &exp);
 105       ASSERT (exp == i - 1);
 106       ASSERT (mantissa == 1.73205);
 107     }
 108   for (; i >= DBL_MIN_EXP - 100 && x > 0.0; i--, x *= 0.5)
 109     {
 110       int exp = -9999;
 111       double mantissa = printf_frexp (x, &exp);
 112       ASSERT (exp == DBL_MIN_EXP - 1);
 113       ASSERT (mantissa >= my_ldexp (1.0, i - DBL_MIN_EXP));
 114       ASSERT (mantissa <= my_ldexp (2.0, i - DBL_MIN_EXP));
 115       ASSERT (mantissa == my_ldexp (x, - exp));
 116     }
 117
 118   return test_exit_status;
 119 }