math/divtc3.c

   1 /* Copyright (C) 2005-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Richard Henderson <rth@redhat.com>, 2005.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <stdbool.h>
  20 #include <math.h>
  21 #include <complex.h>
  22
  23 attribute_hidden
  24 long double _Complex
  25 __divtc3 (long double a, long double b, long double c, long double d)
  26 {
  27   long double denom, ratio, x, y;
  28
  29   /* ??? We can get better behavior from logarithmic scaling instead of
  30      the division.  But that would mean starting to link libgcc against
  31      libm.  We could implement something akin to ldexp/frexp as gcc builtins
  32      fairly easily...  */
  33   if (fabsl (c) < fabsl (d))
  34     {
  35       ratio = c / d;
  36       denom = (c * ratio) + d;
  37       x = ((a * ratio) + b) / denom;
  38       y = ((b * ratio) - a) / denom;
  39     }
  40   else
  41     {
  42       ratio = d / c;
  43       denom = (d * ratio) + c;
  44       x = ((b * ratio) + a) / denom;
  45       y = (b - (a * ratio)) / denom;
  46     }
  47
  48   /* Recover infinities and zeros that computed as NaN+iNaN; the only cases
  49      are nonzero/zero, infinite/finite, and finite/infinite.  */
  50   if (isnan (x) && isnan (y))
  51     {
  52       if (denom == 0.0 && (!isnan (a) || !isnan (b)))
  53         {
  54           x = __copysignl (INFINITY, c) * a;
  55           y = __copysignl (INFINITY, c) * b;
  56         }
  57       else if ((isinf (a) || isinf (b))
  58                && isfinite (c) && isfinite (d))
  59         {
  60           a = __copysignl (isinf (a) ? 1 : 0, a);
  61           b = __copysignl (isinf (b) ? 1 : 0, b);
  62           x = INFINITY * (a * c + b * d);
  63           y = INFINITY * (b * c - a * d);
  64         }
  65       else if ((isinf (c) || isinf (d))
  66                && isfinite (a) && isfinite (b))
  67         {
  68           c = __copysignl (isinf (c) ? 1 : 0, c);
  69           d = __copysignl (isinf (d) ? 1 : 0, d);
  70           x = 0.0 * (a * c + b * d);
  71           y = 0.0 * (b * c - a * d);
  72         }
  73     }
  74
  75   return x + I * y;
  76 }