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/* Copyright (C) 1995-2024 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <ieee754.h>
#include <errno.h>
#include <float.h>
#include <math.h>
#include "gmp.h"
#include "gmp-impl.h"
/* Convert a multi-precision integer of the needed number of bits (106
for long double) and an integral power of two to a `long double' in
IBM extended format. */
long double
__mpn_construct_long_double (mp_srcptr frac_ptr, int expt, int sign)
{
union ibm_extended_long_double u;
unsigned long lzcount;
unsigned long long hi, lo;
int exponent2;
u.d[0].ieee.negative = sign;
u.d[1].ieee.negative = sign;
u.d[0].ieee.exponent = expt + IEEE754_DOUBLE_BIAS;
u.d[1].ieee.exponent = 0;
exponent2 = expt - 53 + IEEE754_DOUBLE_BIAS;
#if BITS_PER_MP_LIMB == 32
/* The low order 53 bits (52 + hidden) go into the lower double */
lo = frac_ptr[0];
lo |= (frac_ptr[1] & ((1LL << (53 - 32)) - 1)) << 32;
/* The high order 53 bits (52 + hidden) go into the upper double */
hi = (frac_ptr[1] >> (53 - 32)) & ((1 << 11) - 1);
hi |= ((unsigned long long) frac_ptr[2]) << 11;
hi |= ((unsigned long long) frac_ptr[3]) << (32 + 11);
#elif BITS_PER_MP_LIMB == 64
/* The low order 53 bits (52 + hidden) go into the lower double */
lo = frac_ptr[0] & (((mp_limb_t) 1 << 53) - 1);
/* The high order 53 bits (52 + hidden) go into the upper double */
hi = (frac_ptr[0] >> 53) & (((mp_limb_t) 1 << 11) - 1);
hi |= (frac_ptr[1] << 11);
#else
#error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
#endif
if ((hi & (1LL << 52)) == 0 && (hi | lo) != 0)
{
/* denormal number */
unsigned long long val = hi ? hi : lo;
if (sizeof (val) == sizeof (long))
lzcount = __builtin_clzl (val);
else if ((val >> 32) != 0)
lzcount = __builtin_clzl ((long) (val >> 32));
else
lzcount = __builtin_clzl ((long) val) + 32;
if (hi)
lzcount = lzcount - (64 - 53);
else
lzcount = lzcount + 53 - (64 - 53);
if (lzcount > u.d[0].ieee.exponent)
{
lzcount = u.d[0].ieee.exponent;
u.d[0].ieee.exponent = 0;
exponent2 -= lzcount;
}
else
{
u.d[0].ieee.exponent -= (lzcount - 1);
exponent2 -= (lzcount - 1);
}
if (lzcount <= 53)
{
hi = (hi << lzcount) | (lo >> (53 - lzcount));
lo = (lo << lzcount) & ((1LL << 53) - 1);
}
else
{
hi = lo << (lzcount - 53);
lo = 0;
}
}
if (lo != 0)
{
/* hidden bit of low double controls rounding of the high double.
If hidden is '1' and either the explicit mantissa is non-zero
or hi is odd, then round up hi and adjust lo (2nd mantissa)
plus change the sign of the low double to compensate. */
if ((lo & (1LL << 52)) != 0
&& ((hi & 1) != 0 || (lo & ((1LL << 52) - 1)) != 0))
{
hi++;
if ((hi & (1LL << 53)) != 0)
{
hi >>= 1;
u.d[0].ieee.exponent++;
if (u.d[0].ieee.exponent == IEEE754_DOUBLE_BIAS + DBL_MAX_EXP)
{
/* Overflow. The appropriate overflowed result must
be produced (if an infinity, that means the low
part must be zero). */
__set_errno (ERANGE);
return (sign ? -LDBL_MAX : LDBL_MAX) * LDBL_MAX;
}
}
u.d[1].ieee.negative = !sign;
lo = (1LL << 53) - lo;
}
/* Normalize the low double. Shift the mantissa left until
the hidden bit is '1' and adjust the exponent accordingly. */
if (sizeof (lo) == sizeof (long))
lzcount = __builtin_clzl (lo);
else if ((lo >> 32) != 0)
lzcount = __builtin_clzl ((long) (lo >> 32));
else
lzcount = __builtin_clzl ((long) lo) + 32;
lzcount = lzcount - (64 - 53);
lo <<= lzcount;
exponent2 -= lzcount;
if (exponent2 > 0)
u.d[1].ieee.exponent = exponent2;
else if (exponent2 > -53)
lo >>= 1 - exponent2;
else
lo = 0;
}
else
u.d[1].ieee.negative = 0;
u.d[1].ieee.mantissa1 = lo;
u.d[1].ieee.mantissa0 = lo >> 32;
u.d[0].ieee.mantissa1 = hi;
u.d[0].ieee.mantissa0 = hi >> 32;
return u.ld;
}
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