libquadmath/math/remquoq.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 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, write to the Free
  19    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20    02111-1307 USA.  */
  21
  22 #include "quadmath-imp.h"
  23
  24
  25 static const __float128 zero = 0.0;
  26
  27
  28 __float128
  29 remquoq (__float128 x, __float128 y, int *quo)
  30 {
  31   int64_t hx,hy;
  32   uint64_t sx,lx,ly,qs;
  33   int cquo;
  34
  35   GET_FLT128_WORDS64 (hx, lx, x);
  36   GET_FLT128_WORDS64 (hy, ly, y);
  37   sx = hx & 0x8000000000000000ULL;
  38   qs = sx ^ (hy & 0x8000000000000000ULL);
  39   hy &= 0x7fffffffffffffffLL;
  40   hx &= 0x7fffffffffffffffLL;
  41
  42   /* Purge off exception values.  */
  43   if ((hy | ly) == 0)
  44     return (x * y) / (x * y);                   /* y = 0 */
  45   if ((hx >= 0x7fff000000000000LL)              /* x not finite */
  46       || ((hy >= 0x7fff000000000000LL)          /* y is NaN */
  47           && (((hy - 0x7fff000000000000LL) | ly) != 0)))
  48     return (x * y) / (x * y);
  49
  50   if (hy <= 0x7ffbffffffffffffLL)
  51     x = fmodq (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  = fabsq (x);
  60   y  = fabsq (y);
  61   cquo = 0;
  62
  63   if (hy <= 0x7ffcffffffffffffLL && x >= 4 * y)
  64     {
  65       x -= 4 * y;
  66       cquo += 4;
  67     }
  68   if (hy <= 0x7ffdffffffffffffLL && x >= 2 * y)
  69     {
  70       x -= 2 * y;
  71       cquo += 2;
  72     }
  73
  74   if (hy < 0x0002000000000000LL)
  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       __float128 y_half = 0.5Q * 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 == 0.0Q)
 106     x = 0.0Q;
 107   if (sx)
 108     x = -x;
 109   return x;
 110 }