1/* Copyright (C) 1995,1996,1997,1998,2002,2003 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, write to the Free
16   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
17   02111-1307 USA.  */
18
19#include "gmp.h"
20#include "gmp-impl.h"
21#include "longlong.h"
22#include <ieee754.h>
23#include <float.h>
24#include <math.h>
25#include <stdlib.h>
26
27/* Convert a `long double' in IEEE854 standard double-precision format to a
28   multi-precision integer representing the significand scaled up by its
29   number of bits (64 for long double) and an integral power of two
30   (MPN frexpl). */
31
32mp_size_t
33__mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size,
34			   int *expt, int *is_neg,
35			   long double value)
36{
37  union ieee854_long_double u;
38  u.d = value;
39
40  *is_neg = u.ieee.negative;
41  *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;
42
43#if BITS_PER_MP_LIMB == 32
44  res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */
45  res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits.  */
46  #define N 2
47#elif BITS_PER_MP_LIMB == 64
48  /* Hopefully the compiler will combine the two bitfield extracts
49     and this composition into just the original quadword extract.  */
50  res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
51  #define N 1
52#else
53  #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
54#endif
55
56  if (u.ieee.exponent == 0)
57    {
58      /* A biased exponent of zero is a special case.
59	 Either it is a zero or it is a denormal number.  */
60      if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
61	/* It's zero.  */
62	*expt = 0;
63      else
64	{
65          /* It is a denormal number, meaning it has no implicit leading
66  	     one bit, and its exponent is in fact the format minimum.  */
67	  int cnt;
68
69	  if (res_ptr[N - 1] != 0)
70	    {
71	      count_leading_zeros (cnt, res_ptr[N - 1]);
72	      if (cnt != 0)
73		{
74#if N == 2
75	          res_ptr[N - 1] = res_ptr[N - 1] << cnt
76			           | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
77	          res_ptr[0] <<= cnt;
78#else
79	          res_ptr[N - 1] <<= cnt;
80#endif
81		}
82	      *expt = LDBL_MIN_EXP - 1 - cnt;
83	    }
84	  else
85	    {
86	      count_leading_zeros (cnt, res_ptr[0]);
87	      res_ptr[N - 1] = res_ptr[0] << cnt;
88	      res_ptr[0] = 0;
89	      *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
90	    }
91	}
92    }
93
94  return N;
95}
96