math/divtc3.c

   1 /* Copyright (C) 2005-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <stdbool.h>
  19 #include <math.h>
  20 #include <complex.h>
  21
  22 attribute_hidden
  23 long double _Complex
  24 __divtc3 (long double a, long double b, long double c, long double d)
  25 {
  26   long double denom, ratio, x, y;
  27
  28   /* ??? We can get better behavior from logarithmic scaling instead of
  29      the division.  But that would mean starting to link libgcc against
  30      libm.  We could implement something akin to ldexp/frexp as gcc builtins
  31      fairly easily...  */
  32   if (fabsl (c) < fabsl (d))
  33     {
  34       ratio = c / d;
  35       denom = (c * ratio) + d;
  36       x = ((a * ratio) + b) / denom;
  37       y = ((b * ratio) - a) / denom;
  38     }
  39   else
  40     {
  41       ratio = d / c;
  42       denom = (d * ratio) + c;
  43       x = ((b * ratio) + a) / denom;
  44       y = (b - (a * ratio)) / denom;
  45     }
  46
  47   /* Recover infinities and zeros that computed as NaN+iNaN; the only cases
  48      are nonzero/zero, infinite/finite, and finite/infinite.  */
  49   if (isnan (x) && isnan (y))
  50     {
  51       if (denom == 0.0 && (!isnan (a) || !isnan (b)))
  52         {
  53           x = copysignl (INFINITY, c) * a;
  54           y = copysignl (INFINITY, c) * b;
  55         }
  56       else if ((isinf (a) || isinf (b))
  57                && isfinite (c) && isfinite (d))
  58         {
  59           a = copysignl (isinf (a) ? 1 : 0, a);
  60           b = copysignl (isinf (b) ? 1 : 0, b);
  61           x = INFINITY * (a * c + b * d);
  62           y = INFINITY * (b * c - a * d);
  63         }
  64       else if ((isinf (c) || isinf (d))
  65                && 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 }