tests/test-trunc2.c

   1 /* Test of rounding towards zero.
   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 /* 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 <stdint.h>
  28 #include <stdio.h>
  29
  30 #include "isnand-nolibm.h"
  31 #include "minus-zero.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/trunc.c.  */
  42
  43 #define DOUBLE double
  44 #define MANT_DIG DBL_MANT_DIG
  45 #define L_(literal) literal
  46
  47 /* -0.0.  See minus-zero.h.  */
  48 #define MINUS_ZERO minus_zerod
  49
  50 /* 2^(MANT_DIG-1).  */
  51 static const DOUBLE TWO_MANT_DIG =
  52   /* Assume MANT_DIG <= 5 * 31.
  53      Use the identity
  54        n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
  55   (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
  56   * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
  57   * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
  58   * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
  59   * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
  60
  61 DOUBLE
  62 trunc_reference (DOUBLE x)
  63 {
  64   /* The use of 'volatile' guarantees that excess precision bits are dropped
  65      at each addition step and before the following comparison at the caller's
  66      site.  It is necessary on x86 systems where double-floats are not IEEE
  67      compliant by default, to avoid that the results become platform and compiler
  68      option dependent.  'volatile' is a portable alternative to gcc's
  69      -ffloat-store option.  */
  70   volatile DOUBLE y = x;
  71   volatile DOUBLE z = y;
  72
  73   if (z > L_(0.0))
  74     {
  75       /* For 0 < x < 1, return +0.0 even if the current rounding mode is
  76          FE_DOWNWARD.  */
  77       if (z < L_(1.0))
  78         z = L_(0.0);
  79       /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
  80       else if (z < TWO_MANT_DIG)
  81         {
  82           /* Round to the next integer (nearest or up or down, doesn't matter).  */
  83           z += TWO_MANT_DIG;
  84           z -= TWO_MANT_DIG;
  85           /* Enforce rounding down.  */
  86           if (z > y)
  87             z -= L_(1.0);
  88         }
  89     }
  90   else if (z < L_(0.0))
  91     {
  92       /* For -1 < x < 0, return -0.0 regardless of the current rounding
  93          mode.  */
  94       if (z > L_(-1.0))
  95         z = MINUS_ZERO;
  96       /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1.  */
  97       else if (z > - TWO_MANT_DIG)
  98         {
  99           /* Round to the next integer (nearest or up or down, doesn't matter).  */
 100           z -= TWO_MANT_DIG;
 101           z += TWO_MANT_DIG;
 102           /* Enforce rounding up.  */
 103           if (z < y)
 104             z += L_(1.0);
 105         }
 106     }
 107   return z;
 108 }
 109
 110
 111 /* Test for equality.  */
 112 static int
 113 equal (DOUBLE x, DOUBLE y)
 114 {
 115   return (isnand (x) ? isnand (y) : x == y);
 116 }
 117
 118 /* Test whether the result for a given argument is correct.  */
 119 static bool
 120 correct_result_p (DOUBLE x, DOUBLE result)
 121 {
 122   return
 123     (x >= 0
 124      ? (x < 1 ? result == L_(0.0) :
 125         x - 1 < x ? result <= x && result >= x - 1 && x - result < 1 :
 126         equal (result, x))
 127      : (x > -1 ? result == L_(0.0) :
 128         x + 1 > x ? result >= x && result <= x + 1 && result - x < 1 :
 129         equal (result, x)));
 130 }
 131
 132 /* Test the function for a given argument.  */
 133 static int
 134 check (double x)
 135 {
 136   /* If the reference implementation is incorrect, bail out immediately.  */
 137   double reference = trunc_reference (x);
 138   ASSERT (correct_result_p (x, reference));
 139   /* If the actual implementation is wrong, return an error code.  */
 140   {
 141     double result = trunc (x);
 142     if (correct_result_p (x, result))
 143       return 0;
 144     else
 145       {
 146 #if GNULIB_TEST_FPRINTF_POSIX
 147         fprintf (stderr, "trunc %g(%a) = %g(%a) or %g(%a)?\n",
 148                  x, x, reference, reference, result, result);
 149 #endif
 150         return 1;
 151       }
 152   }
 153 }
 154
 155 #define NUM_HIGHBITS 13
 156 #define NUM_LOWBITS 4
 157
 158 int
 159 main ()
 160 {
 161   unsigned int highbits;
 162   unsigned int lowbits;
 163   int error = 0;
 164   for (highbits = 0; highbits < (1 << NUM_HIGHBITS); highbits++)
 165     for (lowbits = 0; lowbits < (1 << NUM_LOWBITS); lowbits++)
 166       {
 167         /* Combine highbits and lowbits into a floating-point number,
 168            sign-extending the lowbits to 32-NUM_HIGHBITS bits.  */
 169         union { double f; uint64_t i; } janus;
 170         janus.i = ((uint64_t) highbits << (64 - NUM_HIGHBITS))
 171                   | ((uint64_t) ((int64_t) ((uint64_t) lowbits << (64 - NUM_LOWBITS))
 172                                  >> (64 - NUM_LOWBITS - NUM_HIGHBITS))
 173                      >> NUM_HIGHBITS);
 174         error |= check (janus.f);
 175       }
 176   return (error ? 1 : test_exit_status);
 177 }