1/* Copyright (C) 1993, 1994, 1995, 1996, 1997 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 <stdlib.h>
25
26/* Convert a `double' in IEEE754 standard double-precision format to a
27   multi-precision integer representing the significand scaled up by its
28   number of bits (52 for double) and an integral power of two (MPN frexp). */
29
30mp_size_t
31__mpn_extract_double (mp_ptr res_ptr, mp_size_t size,
32		      int *expt, int *is_neg,
33		      double value)
34{
35  union ieee754_double u;
36  u.d = value;
37
38  *is_neg = u.ieee.negative;
39  *expt = (int) u.ieee.exponent - IEEE754_DOUBLE_BIAS;
40
41#if BITS_PER_MP_LIMB == 32
42  res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */
43  res_ptr[1] = u.ieee.mantissa0; /* High-order 20 bits.  */
44  #define N 2
45#elif BITS_PER_MP_LIMB == 64
46  /* Hopefully the compiler will combine the two bitfield extracts
47     and this composition into just the original quadword extract.  */
48  res_ptr[0] = ((unsigned long int) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
49  #define N 1
50#else
51  #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
52#endif
53/* The format does not fill the last limb.  There are some zeros.  */
54#define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
55			   - (DBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
56
57  if (u.ieee.exponent == 0)
58    {
59      /* A biased exponent of zero is a special case.
60	 Either it is a zero or it is a denormal number.  */
61      if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
62	/* It's zero.  */
63	*expt = 0;
64      else
65	{
66          /* It is a denormal number, meaning it has no implicit leading
67	     one bit, and its exponent is in fact the format minimum.  */
68	  int cnt;
69
70	  if (res_ptr[N - 1] != 0)
71	    {
72	      count_leading_zeros (cnt, res_ptr[N - 1]);
73	      cnt -= NUM_LEADING_ZEROS;
74#if N == 2
75	      res_ptr[N - 1] = res_ptr[1] << cnt
76			       | (N - 1)
77			         * (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
78	      res_ptr[0] <<= cnt;
79#else
80	      res_ptr[N - 1] <<= cnt;
81#endif
82	      *expt = DBL_MIN_EXP - 1 - cnt;
83	    }
84	  else
85	    {
86	      count_leading_zeros (cnt, res_ptr[0]);
87	      if (cnt >= NUM_LEADING_ZEROS)
88		{
89		  res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
90		  res_ptr[0] = 0;
91		}
92	      else
93		{
94		  res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
95		  res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
96		}
97	      *expt = DBL_MIN_EXP - 1
98		      - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
99	    }
100	}
101    }
102  else
103    /* Add the implicit leading one bit for a normalized number.  */
104    res_ptr[N - 1] |= 1L << (DBL_MANT_DIG - 1 - ((N - 1) * BITS_PER_MP_LIMB));
105
106  return N;
107}
108