sysdeps/ieee754/dbl-64/wordsize-64/s_frexp.c

   1 /* Copyright (C) 2011-2014 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.
   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    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <inttypes.h>
  20 #include <math.h>
  21 #include <math_private.h>
  22
  23 /*
  24  * for non-zero, finite x
  25  *      x = frexp(arg,&exp);
  26  * return a double fp quantity x such that 0.5 <= |x| <1.0
  27  * and the corresponding binary exponent "exp". That is
  28  *      arg = x*2^exp.
  29  * If arg is inf, 0.0, or NaN, then frexp(arg,&exp) returns arg
  30  * with *exp=0.
  31  */
  32
  33
  34 double
  35 __frexp (double x, int *eptr)
  36 {
  37   int64_t ix;
  38   EXTRACT_WORDS64 (ix, x);
  39   int32_t ex = 0x7ff & (ix >> 52);
  40   int e = 0;
  41
  42   if (__builtin_expect (ex != 0x7ff && x != 0.0, 1))
  43     {
  44       /* Not zero and finite.  */
  45       e = ex - 1022;
  46       if (__builtin_expect (ex == 0, 0))
  47         {
  48           /* Subnormal.  */
  49           x *= 0x1p54;
  50           EXTRACT_WORDS64 (ix, x);
  51           ex = 0x7ff & (ix >> 52);
  52           e = ex - 1022 - 54;
  53         }
  54
  55       ix = (ix & INT64_C (0x800fffffffffffff)) | INT64_C (0x3fe0000000000000);
  56       INSERT_WORDS64 (x, ix);
  57     }
  58
  59   *eptr = e;
  60   return x;
  61 }
  62 weak_alias (__frexp, frexp)
  63 #ifdef NO_LONG_DOUBLE
  64 strong_alias (__frexp, __frexpl)
  65 weak_alias (__frexp, frexpl)
  66 #endif