tests/test-floor2.c

   1 /* Test of rounding towards negative infinity.
   2    Copyright (C) 2007-2020 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 /* When this test fails on some platform, build it together with the gnulib
  20    module 'fprintf-posix' for optimal debugging output.  */
  21
  22 #include <config.h>
  23
  24 #include <math.h>
  25
  26 #include <float.h>
  27 #include <stdbool.h>
  28 #include <stdint.h>
  29 #include <stdio.h>
  30
  31 #include "isnand-nolibm.h"
  32 #include "macros.h"
  33
  34 /* MSVC with option -fp:strict refuses to compile constant initializers that
  35    contain floating-point operations.  Pacify this compiler.  */
  36 #if defined _MSC_VER && !defined __clang__
  37 # pragma fenv_access (off)
  38 #endif
  39
  40
  41 /* The reference implementation, taken from lib/floor.c.  */
  42
  43 #define DOUBLE double
  44 #define MANT_DIG DBL_MANT_DIG
  45 #define L_(literal) literal
  46
  47 /* 2^(MANT_DIG-1).  */
  48 static const DOUBLE TWO_MANT_DIG =
  49   /* Assume MANT_DIG <= 5 * 31.
  50      Use the identity
  51        n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
  52   (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
  53   * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
  54   * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
  55   * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
  56   * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
  57
  58 DOUBLE
  59 floor_reference (DOUBLE x)
  60 {
  61   /* The use of 'volatile' guarantees that excess precision bits are dropped
  62      at each addition step and before the following comparison at the caller's
  63      site.  It is necessary on x86 systems where double-floats are not IEEE
  64      compliant by default, to avoid that the results become platform and compiler
  65      option dependent.  'volatile' is a portable alternative to gcc's
  66      -ffloat-store option.  */
  67   volatile DOUBLE y = x;
  68   volatile DOUBLE z = y;
  69
  70   if (z > L_(0.0))
  71     {
  72       /* For 0 < x < 1, return +0.0 even if the current rounding mode is
  73          FE_DOWNWARD.  */
  74       if (z < L_(1.0))
  75         z = L_(0.0);
  76       /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
  77       else if (z < TWO_MANT_DIG)
  78         {
  79           /* Round to the next integer (nearest or up or down, doesn't matter).  */
  80           z += TWO_MANT_DIG;
  81           z -= TWO_MANT_DIG;
  82           /* Enforce rounding down.  */
  83           if (z > y)
  84             z -= L_(1.0);
  85         }
  86     }
  87   else if (z < L_(0.0))
  88     {
  89       /* Work around ICC's desire to optimize denormal floats to 0.  */
  90       if (z > -DBL_MIN)
  91         return L_(-1.0);
  92       /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1.  */
  93       if (z > - TWO_MANT_DIG)
  94         {
  95           /* Round to the next integer (nearest or up or down, doesn't matter).  */
  96           z -= TWO_MANT_DIG;
  97           z += TWO_MANT_DIG;
  98           /* Enforce rounding down.  */
  99           if (z > y)
 100             z -= L_(1.0);
 101         }
 102     }
 103   return z;
 104 }
 105
 106
 107 /* Test for equality.  */
 108 static int
 109 equal (DOUBLE x, DOUBLE y)
 110 {
 111   return (isnand (x) ? isnand (y) : x == y);
 112 }
 113
 114 /* Test whether the result for a given argument is correct.  */
 115 static bool
 116 correct_result_p (DOUBLE x, DOUBLE result)
 117 {
 118   return
 119     (x < 0 && x >= -1 ? result == - L_(1.0) :
 120      x - 1 < x ? result <= x && result >= x - 1 && x - result < 1 :
 121      equal (result, x));
 122 }
 123
 124 /* Test the function for a given argument.  */
 125 static int
 126 check (double x)
 127 {
 128   /* If the reference implementation is incorrect, bail out immediately.  */
 129   double reference = floor_reference (x);
 130   ASSERT (correct_result_p (x, reference));
 131   /* If the actual implementation is wrong, return an error code.  */
 132   {
 133     double result = floor (x);
 134     if (correct_result_p (x, result))
 135       return 0;
 136     else
 137       {
 138 #if GNULIB_TEST_FPRINTF_POSIX
 139         fprintf (stderr, "floor %g(%a) = %g(%a) or %g(%a)?\n",
 140                  x, x, reference, reference, result, result);
 141 #endif
 142         return 1;
 143       }
 144   }
 145 }
 146
 147 #define NUM_HIGHBITS 15
 148 #define NUM_LOWBITS 4
 149
 150 int
 151 main ()
 152 {
 153 #ifdef UINT64_MAX
 154   unsigned int highbits;
 155   unsigned int lowbits;
 156   int error = 0;
 157   for (highbits = 0; highbits < (1 << NUM_HIGHBITS); highbits++)
 158     for (lowbits = 0; lowbits < (1 << NUM_LOWBITS); lowbits++)
 159       {
 160         /* Combine highbits and lowbits into a floating-point number,
 161            sign-extending the lowbits to 64-NUM_HIGHBITS bits.  */
 162         union { double f; uint64_t i; } janus;
 163         janus.i = ((uint64_t) highbits << (64 - NUM_HIGHBITS))
 164                   | ((uint64_t) ((int64_t) ((uint64_t) lowbits << (64 - NUM_LOWBITS))
 165                                  >> (64 - NUM_LOWBITS - NUM_HIGHBITS))
 166                      >> NUM_HIGHBITS);
 167         error |= check (janus.f);
 168       }
 169   return (error ? 1 : 0);
 170 #else
 171   fprintf (stderr, "Skipping test: no 64-bit integer type available\n");
 172   return 77;
 173 #endif
 174 }