math/multc3.c

   1 /* Copyright (C) 2005-2020 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    <https://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 __multc3 (long double a, long double b, long double c, long double d)
  26 {
  27   long double ac, bd, ad, bc, x, y;
  28
  29   ac = a * c;
  30   bd = b * d;
  31   ad = a * d;
  32   bc = b * c;
  33
  34   x = ac - bd;
  35   y = ad + bc;
  36
  37   if (isnan (x) && isnan (y))
  38     {
  39       /* Recover infinities that computed as NaN + iNaN.  */
  40       bool recalc = 0;
  41       if (isinf (a) || isinf (b))
  42         {
  43           /* z is infinite.  "Box" the infinity and change NaNs in
  44              the other factor to 0.  */
  45           a = copysignl (isinf (a) ? 1 : 0, a);
  46           b = copysignl (isinf (b) ? 1 : 0, b);
  47           if (isnan (c)) c = copysignl (0, c);
  48           if (isnan (d)) d = copysignl (0, d);
  49           recalc = 1;
  50         }
  51      if (isinf (c) || isinf (d))
  52         {
  53           /* w is infinite.  "Box" the infinity and change NaNs in
  54              the other factor to 0.  */
  55           c = copysignl (isinf (c) ? 1 : 0, c);
  56           d = copysignl (isinf (d) ? 1 : 0, d);
  57           if (isnan (a)) a = copysignl (0, a);
  58           if (isnan (b)) b = copysignl (0, b);
  59           recalc = 1;
  60         }
  61      if (!recalc
  62           && (isinf (ac) || isinf (bd)
  63               || isinf (ad) || isinf (bc)))
  64         {
  65           /* Recover infinities from overflow by changing NaNs to 0.  */
  66           if (isnan (a)) a = copysignl (0, a);
  67           if (isnan (b)) b = copysignl (0, b);
  68           if (isnan (c)) c = copysignl (0, c);
  69           if (isnan (d)) d = copysignl (0, d);
  70           recalc = 1;
  71         }
  72       if (recalc)
  73         {
  74           x = INFINITY * (a * c - b * d);
  75           y = INFINITY * (a * d + b * c);
  76         }
  77     }
  78
  79   return x + I * y;
  80 }