sysdeps/ieee754/dbl-64/s_remquo.c

   1 /* Compute remainder and a congruent to the quotient.
   2    Copyright (C) 1997-2018 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 #include <libm-alias-double.h>
  24
  25
  26 static const double zero = 0.0;
  27
  28
  29 double
  30 __remquo (double x, double y, int *quo)
  31 {
  32   int32_t hx, hy;
  33   uint32_t sx, lx, ly;
  34   int cquo, qs;
  35
  36   EXTRACT_WORDS (hx, lx, x);
  37   EXTRACT_WORDS (hy, ly, y);
  38   sx = hx & 0x80000000;
  39   qs = sx ^ (hy & 0x80000000);
  40   hy &= 0x7fffffff;
  41   hx &= 0x7fffffff;
  42
  43   /* Purge off exception values.  */
  44   if ((hy | ly) == 0)
  45     return (x * y) / (x * y);                   /* y = 0 */
  46   if ((hx >= 0x7ff00000)                        /* x not finite */
  47       || ((hy >= 0x7ff00000)                    /* p is NaN */
  48           && (((hy - 0x7ff00000) | ly) != 0)))
  49     return (x * y) / (x * y);
  50
  51   if (hy <= 0x7fbfffff)
  52     x = __ieee754_fmod (x, 8 * y);              /* now x < 8y */
  53
  54   if (((hx - hy) | (lx - ly)) == 0)
  55     {
  56       *quo = qs ? -1 : 1;
  57       return zero * x;
  58     }
  59
  60   x = fabs (x);
  61   y = fabs (y);
  62   cquo = 0;
  63
  64   if (hy <= 0x7fcfffff && x >= 4 * y)
  65     {
  66       x -= 4 * y;
  67       cquo += 4;
  68     }
  69   if (hy <= 0x7fdfffff && x >= 2 * y)
  70     {
  71       x -= 2 * y;
  72       cquo += 2;
  73     }
  74
  75   if (hy < 0x00200000)
  76     {
  77       if (x + x > y)
  78         {
  79           x -= y;
  80           ++cquo;
  81           if (x + x >= y)
  82             {
  83               x -= y;
  84               ++cquo;
  85             }
  86         }
  87     }
  88   else
  89     {
  90       double y_half = 0.5 * y;
  91       if (x > y_half)
  92         {
  93           x -= y;
  94           ++cquo;
  95           if (x >= y_half)
  96             {
  97               x -= y;
  98               ++cquo;
  99             }
 100         }
 101     }
 102
 103   *quo = qs ? -cquo : cquo;
 104
 105   /* Ensure correct sign of zero result in round-downward mode.  */
 106   if (x == 0.0)
 107     x = 0.0;
 108   if (sx)
 109     x = -x;
 110   return x;
 111 }
 112 libm_alias_double (__remquo, remquo)