1/* Copyright (C) 1995-2020 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, see
16 <https://www.gnu.org/licenses/>. */
17
18#include "gmp.h"
19#include "gmp-impl.h"
20#include <ieee754.h>
21#include <float.h>
22
23/* Convert a multi-precision integer of the needed number of bits (53 for
24 double) and an integral power of two to a `double' in IEEE754 double-
25 precision format. */
26
27double
28__mpn_construct_double (mp_srcptr frac_ptr, int expt, int negative)
29{
30 union ieee754_double u;
31
32 u.ieee.negative = negative;
33 u.ieee.exponent = expt + IEEE754_DOUBLE_BIAS;
34#if BITS_PER_MP_LIMB == 32
35 u.ieee.mantissa1 = frac_ptr[0];
36 u.ieee.mantissa0 = frac_ptr[1] & (((mp_limb_t) 1
37 << (DBL_MANT_DIG - 32)) - 1);
38#elif BITS_PER_MP_LIMB == 64
39 u.ieee.mantissa1 = frac_ptr[0] & (((mp_limb_t) 1 << 32) - 1);
40 u.ieee.mantissa0 = (frac_ptr[0] >> 32) & (((mp_limb_t) 1
41 << (DBL_MANT_DIG - 32)) - 1);
42#else
43 # error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
44#endif
45
46 return u.d;
47}
48