math/multc3.c

   1 /* Copyright (C) 2005-2022 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 __multc3 (long double a, long double b, long double c, long double d)
  25 {
  26   long double ac, bd, ad, bc, x, y;
  27
  28   ac = a * c;
  29   bd = b * d;
  30   ad = a * d;
  31   bc = b * c;
  32
  33   x = ac - bd;
  34   y = ad + bc;
  35
  36   if (isnan (x) && isnan (y))
  37     {
  38       /* Recover infinities that computed as NaN + iNaN.  */
  39       bool recalc = 0;
  40       if (isinf (a) || isinf (b))
  41         {
  42           /* z is infinite.  "Box" the infinity and change NaNs in
  43              the other factor to 0.  */
  44           a = copysignl (isinf (a) ? 1 : 0, a);
  45           b = copysignl (isinf (b) ? 1 : 0, b);
  46           if (isnan (c)) c = copysignl (0, c);
  47           if (isnan (d)) d = copysignl (0, d);
  48           recalc = 1;
  49         }
  50      if (isinf (c) || isinf (d))
  51         {
  52           /* w is infinite.  "Box" the infinity and change NaNs in
  53              the other factor to 0.  */
  54           c = copysignl (isinf (c) ? 1 : 0, c);
  55           d = copysignl (isinf (d) ? 1 : 0, d);
  56           if (isnan (a)) a = copysignl (0, a);
  57           if (isnan (b)) b = copysignl (0, b);
  58           recalc = 1;
  59         }
  60      if (!recalc
  61           && (isinf (ac) || isinf (bd)
  62               || isinf (ad) || isinf (bc)))
  63         {
  64           /* Recover infinities from overflow by changing NaNs to 0.  */
  65           if (isnan (a)) a = copysignl (0, a);
  66           if (isnan (b)) b = copysignl (0, b);
  67           if (isnan (c)) c = copysignl (0, c);
  68           if (isnan (d)) d = copysignl (0, d);
  69           recalc = 1;
  70         }
  71       if (recalc)
  72         {
  73           x = INFINITY * (a * c - b * d);
  74           y = INFINITY * (a * d + b * c);
  75         }
  76     }
  77
  78   return x + I * y;
  79 }