lib/ldexpl.c

   1 /* Emulation for ldexpl.
   2    Contributed by Paolo Bonzini
   3
   4    Copyright 2002-2003, 2007-2020 Free Software Foundation, Inc.
   5
   6    This file is part of gnulib.
   7
   8    This program is free software: you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  20
  21 #include <config.h>
  22
  23 /* Specification.  */
  24 #include <math.h>
  25
  26 #if HAVE_SAME_LONG_DOUBLE_AS_DOUBLE
  27
  28 long double
  29 ldexpl (long double x, int exp)
  30 {
  31   return ldexp (x, exp);
  32 }
  33
  34 #else
  35
  36 # include <float.h>
  37 # include "fpucw.h"
  38
  39 long double
  40 ldexpl (long double x, int exp)
  41 {
  42   long double factor;
  43   int bit;
  44   DECL_LONG_DOUBLE_ROUNDING
  45
  46   BEGIN_LONG_DOUBLE_ROUNDING ();
  47
  48   /* Check for zero, nan and infinity. */
  49   if (!(isnanl (x) || x + x == x))
  50     {
  51       if (exp < 0)
  52         {
  53           exp = -exp;
  54           factor = 0.5L;
  55         }
  56       else
  57         factor = 2.0L;
  58
  59       if (exp > 0)
  60         for (bit = 1;;)
  61           {
  62             /* Invariant: Here bit = 2^i, factor = 2^-2^i or = 2^2^i,
  63                and bit <= exp.  */
  64             if (exp & bit)
  65               x *= factor;
  66             bit <<= 1;
  67             if (bit > exp)
  68               break;
  69             factor = factor * factor;
  70           }
  71     }
  72
  73   END_LONG_DOUBLE_ROUNDING ();
  74
  75   return x;
  76 }
  77
  78 #endif
  79
  80 #if 0
  81 int
  82 main (void)
  83 {
  84   long double x;
  85   int y;
  86   for (y = 0; y < 29; y++)
  87     printf ("%5d %.16Lg %.16Lg\n", y, ldexpl (0.8L, y), ldexpl (0.8L, -y) * ldexpl (0.8L, y));
  88 }
  89 #endif