tests/test-floorf2.c

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