sysdeps/ieee754/dbl-64/s_remquo.c

   1 /* Compute remainder and a congruent to the quotient.
   2    Copyright (C) 1997-2017 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <math.h>
  21
  22 #include <math_private.h>
  23
  24
  25 static const double zero = 0.0;
  26
  27
  28 double
  29 __remquo (double x, double y, int *quo)
  30 {
  31   int32_t hx, hy;
  32   u_int32_t sx, lx, ly;
  33   int cquo, qs;
  34
  35   EXTRACT_WORDS (hx, lx, x);
  36   EXTRACT_WORDS (hy, ly, y);
  37   sx = hx & 0x80000000;
  38   qs = sx ^ (hy & 0x80000000);
  39   hy &= 0x7fffffff;
  40   hx &= 0x7fffffff;
  41
  42   /* Purge off exception values.  */
  43   if ((hy | ly) == 0)
  44     return (x * y) / (x * y);                   /* y = 0 */
  45   if ((hx >= 0x7ff00000)                        /* x not finite */
  46       || ((hy >= 0x7ff00000)                    /* p is NaN */
  47           && (((hy - 0x7ff00000) | ly) != 0)))
  48     return (x * y) / (x * y);
  49
  50   if (hy <= 0x7fbfffff)
  51     x = __ieee754_fmod (x, 8 * y);              /* now x < 8y */
  52
  53   if (((hx - hy) | (lx - ly)) == 0)
  54     {
  55       *quo = qs ? -1 : 1;
  56       return zero * x;
  57     }
  58
  59   x = fabs (x);
  60   y = fabs (y);
  61   cquo = 0;
  62
  63   if (hy <= 0x7fcfffff && x >= 4 * y)
  64     {
  65       x -= 4 * y;
  66       cquo += 4;
  67     }
  68   if (hy <= 0x7fdfffff && x >= 2 * y)
  69     {
  70       x -= 2 * y;
  71       cquo += 2;
  72     }
  73
  74   if (hy < 0x00200000)
  75     {
  76       if (x + x > y)
  77         {
  78           x -= y;
  79           ++cquo;
  80           if (x + x >= y)
  81             {
  82               x -= y;
  83               ++cquo;
  84             }
  85         }
  86     }
  87   else
  88     {
  89       double y_half = 0.5 * y;
  90       if (x > y_half)
  91         {
  92           x -= y;
  93           ++cquo;
  94           if (x >= y_half)
  95             {
  96               x -= y;
  97               ++cquo;
  98             }
  99         }
 100     }
 101
 102   *quo = qs ? -cquo : cquo;
 103
 104   /* Ensure correct sign of zero result in round-downward mode.  */
 105   if (x == 0.0)
 106     x = 0.0;
 107   if (sx)
 108     x = -x;
 109   return x;
 110 }
 111 weak_alias (__remquo, remquo)
 112 #ifdef NO_LONG_DOUBLE
 113 strong_alias (__remquo, __remquol)
 114 weak_alias (__remquo, remquol)
 115 #endif