libquadmath/math/remquoq.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 and
   5                   Jakub Jelinek <jj@ultra.linux.cz>, 1999.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <http://www.gnu.org/licenses/>.  */
  20
  21 #include "quadmath-imp.h"
  22
  23 static const __float128 zero = 0.0;
  24
  25
  26 __float128
  27 remquoq (__float128 x, __float128 y, int *quo)
  28 {
  29   int64_t hx,hy;
  30   uint64_t sx,lx,ly,qs;
  31   int cquo;
  32
  33   GET_FLT128_WORDS64 (hx, lx, x);
  34   GET_FLT128_WORDS64 (hy, ly, y);
  35   sx = hx & 0x8000000000000000ULL;
  36   qs = sx ^ (hy & 0x8000000000000000ULL);
  37   hy &= 0x7fffffffffffffffLL;
  38   hx &= 0x7fffffffffffffffLL;
  39
  40   /* Purge off exception values.  */
  41   if ((hy | ly) == 0)
  42     return (x * y) / (x * y);                   /* y = 0 */
  43   if ((hx >= 0x7fff000000000000LL)              /* x not finite */
  44       || ((hy >= 0x7fff000000000000LL)          /* y is NaN */
  45           && (((hy - 0x7fff000000000000LL) | ly) != 0)))
  46     return (x * y) / (x * y);
  47
  48   if (hy <= 0x7ffbffffffffffffLL)
  49     x = fmodq (x, 8 * y);              /* now x < 8y */
  50
  51   if (((hx - hy) | (lx - ly)) == 0)
  52     {
  53       *quo = qs ? -1 : 1;
  54       return zero * x;
  55     }
  56
  57   x  = fabsq (x);
  58   y  = fabsq (y);
  59   cquo = 0;
  60
  61   if (hy <= 0x7ffcffffffffffffLL && x >= 4 * y)
  62     {
  63       x -= 4 * y;
  64       cquo += 4;
  65     }
  66   if (hy <= 0x7ffdffffffffffffLL && x >= 2 * y)
  67     {
  68       x -= 2 * y;
  69       cquo += 2;
  70     }
  71
  72   if (hy < 0x0002000000000000LL)
  73     {
  74       if (x + x > y)
  75         {
  76           x -= y;
  77           ++cquo;
  78           if (x + x >= y)
  79             {
  80               x -= y;
  81               ++cquo;
  82             }
  83         }
  84     }
  85   else
  86     {
  87       __float128 y_half = 0.5Q * y;
  88       if (x > y_half)
  89         {
  90           x -= y;
  91           ++cquo;
  92           if (x >= y_half)
  93             {
  94               x -= y;
  95               ++cquo;
  96             }
  97         }
  98     }
  99
 100   *quo = qs ? -cquo : cquo;
 101
 102   /* Ensure correct sign of zero result in round-downward mode.  */
 103   if (x == 0)
 104     x = 0;
 105   if (sx)
 106     x = -x;
 107   return x;
 108 }