tests/test-truncf2.c

   1 /* Test of rounding towards zero.
   2    Copyright (C) 2007-2021 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 "isnanf-nolibm.h"
  32 #include "minus-zero.h"
  33 #include "macros.h"
  34
  35 /* MSVC with option -fp:strict refuses to compile constant initializers that
  36    contain floating-point operations.  Pacify this compiler.  */
  37 #if defined _MSC_VER && !defined __clang__
  38 # pragma fenv_access (off)
  39 #endif
  40
  41
  42 /* The reference implementation, taken from lib/trunc.c.  */
  43
  44 #define DOUBLE float
  45 #define MANT_DIG FLT_MANT_DIG
  46 #define L_(literal) literal##f
  47
  48 /* -0.0.  See minus-zero.h.  */
  49 #define MINUS_ZERO minus_zerof
  50
  51 /* 2^(MANT_DIG-1).  */
  52 static const DOUBLE TWO_MANT_DIG =
  53   /* Assume MANT_DIG <= 5 * 31.
  54      Use the identity
  55        n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5).  */
  56   (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
  57   * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
  58   * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
  59   * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
  60   * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
  61
  62 DOUBLE
  63 truncf_reference (DOUBLE x)
  64 {
  65   /* The use of 'volatile' guarantees that excess precision bits are dropped
  66      at each addition step and before the following comparison at the caller's
  67      site.  It is necessary on x86 systems where double-floats are not IEEE
  68      compliant by default, to avoid that the results become platform and compiler
  69      option dependent.  'volatile' is a portable alternative to gcc's
  70      -ffloat-store option.  */
  71   volatile DOUBLE y = x;
  72   volatile DOUBLE z = y;
  73
  74   if (z > L_(0.0))
  75     {
  76       /* For 0 < x < 1, return +0.0 even if the current rounding mode is
  77          FE_DOWNWARD.  */
  78       if (z < L_(1.0))
  79         z = L_(0.0);
  80       /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1.  */
  81       else if (z < TWO_MANT_DIG)
  82         {
  83           /* Round to the next integer (nearest or up or down, doesn't matter).  */
  84           z += TWO_MANT_DIG;
  85           z -= TWO_MANT_DIG;
  86           /* Enforce rounding down.  */
  87           if (z > y)
  88             z -= L_(1.0);
  89         }
  90     }
  91   else if (z < L_(0.0))
  92     {
  93       /* For -1 < x < 0, return -0.0 regardless of the current rounding
  94          mode.  */
  95       if (z > L_(-1.0))
  96         z = MINUS_ZERO;
  97       /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1.  */
  98       else if (z > - TWO_MANT_DIG)
  99         {
 100           /* Round to the next integer (nearest or up or down, doesn't matter).  */
 101           z -= TWO_MANT_DIG;
 102           z += TWO_MANT_DIG;
 103           /* Enforce rounding up.  */
 104           if (z < y)
 105             z += L_(1.0);
 106         }
 107     }
 108   return z;
 109 }
 110
 111
 112 /* Test for equality.  */
 113 static int
 114 equal (DOUBLE x, DOUBLE y)
 115 {
 116   return (isnanf (x) ? isnanf (y) : x == y);
 117 }
 118
 119 /* Test whether the result for a given argument is correct.  */
 120 static bool
 121 correct_result_p (DOUBLE x, DOUBLE result)
 122 {
 123   return
 124     (x >= 0
 125      ? (x < 1 ? result == L_(0.0) :
 126         x - 1 < x ? result <= x && result >= x - 1 && x - result < 1 :
 127         equal (result, x))
 128      : (x > -1 ? result == L_(0.0) :
 129         x + 1 > x ? result >= x && result <= x + 1 && result - x < 1 :
 130         equal (result, x)));
 131 }
 132
 133 /* Test the function for a given argument.  */
 134 static int
 135 check (float x)
 136 {
 137   /* If the reference implementation is incorrect, bail out immediately.  */
 138   float reference = truncf_reference (x);
 139   ASSERT (correct_result_p (x, reference));
 140   /* If the actual implementation is wrong, return an error code.  */
 141   {
 142     float result = truncf (x);
 143     if (correct_result_p (x, result))
 144       return 0;
 145     else
 146       {
 147 #if GNULIB_TEST_FPRINTF_POSIX
 148         fprintf (stderr, "truncf %g(%a) = %g(%a) or %g(%a)?\n",
 149                  x, x, reference, reference, result, result);
 150 #endif
 151         return 1;
 152       }
 153   }
 154 }
 155
 156 #define NUM_HIGHBITS 12
 157 #define NUM_LOWBITS 4
 158
 159 int
 160 main ()
 161 {
 162   unsigned int highbits;
 163   unsigned int lowbits;
 164   int error = 0;
 165   for (highbits = 0; highbits < (1 << NUM_HIGHBITS); highbits++)
 166     for (lowbits = 0; lowbits < (1 << NUM_LOWBITS); lowbits++)
 167       {
 168         /* Combine highbits and lowbits into a floating-point number,
 169            sign-extending the lowbits to 32-NUM_HIGHBITS bits.  */
 170         union { float f; uint32_t i; } janus;
 171         janus.i = ((uint32_t) highbits << (32 - NUM_HIGHBITS))
 172                   | ((uint32_t) ((int32_t) ((uint32_t) lowbits << (32 - NUM_LOWBITS))
 173                                  >> (32 - NUM_LOWBITS - NUM_HIGHBITS))
 174                      >> NUM_HIGHBITS);
 175         error |= check (janus.f);
 176       }
 177   return (error ? 1 : 0);
 178 }