math/divtc3.c

   1 /* Copyright (C) 2005, 2006 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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 #include <stdbool.h>
  21 #include <math.h>
  22 #include <complex.h>
  23
  24 attribute_hidden
  25 long double _Complex
  26 __divtc3 (long double a, long double b, long double c, long double d)
  27 {
  28   long double denom, ratio, x, y;
  29
  30   /* ??? We can get better behavior from logarithmic scaling instead of
  31      the division.  But that would mean starting to link libgcc against
  32      libm.  We could implement something akin to ldexp/frexp as gcc builtins
  33      fairly easily...  */
  34   if (fabsl (c) < fabsl (d))
  35     {
  36       ratio = c / d;
  37       denom = (c * ratio) + d;
  38       x = ((a * ratio) + b) / denom;
  39       y = ((b * ratio) - a) / denom;
  40     }
  41   else
  42     {
  43       ratio = d / c;
  44       denom = (d * ratio) + c;
  45       x = ((b * ratio) + a) / denom;
  46       y = (b - (a * ratio)) / denom;
  47     }
  48
  49   /* Recover infinities and zeros that computed as NaN+iNaN; the only cases
  50      are nonzero/zero, infinite/finite, and finite/infinite.  */
  51   if (isnan (x) && isnan (y))
  52     {
  53       if (denom == 0.0 && (!isnan (a) || !isnan (b)))
  54         {
  55           x = __copysignl (INFINITY, c) * a;
  56           y = __copysignl (INFINITY, c) * b;
  57         }
  58       else if ((isinf (a) || isinf (b)) && 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)) && isfinite (a) && isfinite (b))
  66         {
  67           c = __copysignl (isinf (c) ? 1 : 0, c);
  68           d = __copysignl (isinf (d) ? 1 : 0, d);
  69           x = 0.0 * (a * c + b * d);
  70           y = 0.0 * (b * c - a * d);
  71         }
  72     }
  73
  74   return x + I * y;
  75 }