1/* Copyright (C) 1995, 1996, 1997, 2000, 2007 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 `long double' in IEEE854 standard double-precision format to a
27   multi-precision integer representing the significand scaled up by its
28   number of bits (64 for long double) and an integral power of two
29   (MPN frexpl). */
30
31mp_size_t
32__mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size,
33			   int *expt, int *is_neg,
34			   long double value)
35{
36  union ieee854_long_double u;
37  u.d = value;
38
39  *is_neg = u.ieee.negative;
40  *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;
41
42#if BITS_PER_MP_LIMB == 32
43  res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction.  */
44  res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits.  */
45  #define N 2
46#elif BITS_PER_MP_LIMB == 64
47  /* Hopefully the compiler will combine the two bitfield extracts
48     and this composition into just the original quadword extract.  */
49  res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
50  #define N 1
51#else
52  #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
53#endif
54
55  if (u.ieee.exponent == 0)
56    {
57      /* A biased exponent of zero is a special case.
58	 Either it is a zero or it is a denormal number.  */
59      if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2.  */
60	/* It's zero.  */
61	*expt = 0;
62      else
63	{
64	  /* It is a denormal number, meaning it has no implicit leading
65	     one bit, and its exponent is in fact the format minimum.  */
66	  int cnt;
67
68	  /* One problem with Intel's 80-bit format is that the explicit
69	     leading one in the normalized representation has to be zero
70	     for denormalized number.  If it is one, the number is according
71	     to Intel's specification an invalid number.  We make the
72	     representation unique by explicitly clearing this bit.  */
73	  res_ptr[N - 1] &= ~(1L << ((LDBL_MANT_DIG - 1) % BITS_PER_MP_LIMB));
74
75	  if (res_ptr[N - 1] != 0)
76	    {
77	      count_leading_zeros (cnt, res_ptr[N - 1]);
78	      if (cnt != 0)
79		{
80#if N == 2
81		  res_ptr[N - 1] = res_ptr[N - 1] << cnt
82				   | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
83		  res_ptr[0] <<= cnt;
84#else
85		  res_ptr[N - 1] <<= cnt;
86#endif
87		}
88	      *expt = LDBL_MIN_EXP - 1 - cnt;
89	    }
90	  else if (res_ptr[0] != 0)
91	    {
92	      count_leading_zeros (cnt, res_ptr[0]);
93	      res_ptr[N - 1] = res_ptr[0] << cnt;
94	      res_ptr[0] = 0;
95	      *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
96	    }
97	  else
98	    {
99	      /* This is the special case of the pseudo denormal number
100		 with only the implicit leading bit set.  The value is
101		 in fact a normal number and so we have to treat this
102		 case differently.  */
103#if N == 2
104	      res_ptr[N - 1] = 0x80000000ul;
105#else
106	      res_ptr[0] = 0x8000000000000000ul;
107#endif
108	      *expt = LDBL_MIN_EXP - 1;
109	    }
110	}
111    }
112  else if (u.ieee.exponent < 0x7fff
113#if N == 2
114	   && res_ptr[0] == 0
115#endif
116	   && res_ptr[N - 1] == 0)
117    /* Pseudo zero.  */
118    *expt = 0;
119
120  return N;
121}
122