mirror of git://sourceware.org/git/glibc.git
104 lines
3.5 KiB
C
104 lines
3.5 KiB
C
/* Copyright (C) 1995, 1996, 1997, 1998, 1999, 2002, 2003, 2004, 2006
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Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, write to the Free
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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#include <ieee754.h>
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#include <float.h>
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#include <math.h>
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/* Convert a multi-precision integer of the needed number of bits (106
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for long double) and an integral power of two to a `long double' in
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IBM extended format. */
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long double
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__mpn_construct_long_double (mp_srcptr frac_ptr, int expt, int sign)
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{
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union ibm_extended_long_double u;
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unsigned long hidden2, lzcount;
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unsigned long long hi, lo;
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u.ieee.negative = sign;
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u.ieee.negative2 = sign;
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u.ieee.exponent = expt + IBM_EXTENDED_LONG_DOUBLE_BIAS;
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u.ieee.exponent2 = expt - 53 + IBM_EXTENDED_LONG_DOUBLE_BIAS;
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#if BITS_PER_MP_LIMB == 32
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/* The low order 53 bits (52 + hidden) go into the lower double */
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lo = frac_ptr[0];
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lo |= (frac_ptr[1] & ((1LL << (53 - 32)) - 1)) << 32;
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hidden2 = (frac_ptr[1] >> (52 - 32)) & ((mp_limb_t) 1);
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/* The high order 53 bits (52 + hidden) go into the upper double */
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hi = (frac_ptr[1] >> (53 - 32)) & ((1 << 11) - 1);
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hi |= ((unsigned long long) frac_ptr[2]) << 11;
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hi |= ((unsigned long long) frac_ptr[3]) << (32 + 11);
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#elif BITS_PER_MP_LIMB == 64
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/* The low order 53 bits (52 + hidden) go into the lower double */
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lo = frac_ptr[0] & (((mp_limb_t) 1 << 53) - 1);
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hidden2 = (frac_ptr[0] >> 52) & ((mp_limb_t) 1);
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/* The high order 53 bits (52 + hidden) go into the upper double */
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hi = (frac_ptr[0] >> 53) & (((mp_limb_t) 1 << 11) - 1);
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hi |= (frac_ptr[1] << 11);
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#else
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#error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
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#endif
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if (lo != 0L)
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{
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/* hidden2 bit of low double controls rounding of the high double.
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If hidden2 is '1' then round up hi and adjust lo (2nd mantissa)
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plus change the sign of the low double to compensate. */
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if (hidden2)
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{
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hi++;
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u.ieee.negative2 = !sign;
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lo = (1LL << 53) - lo;
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}
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/* The hidden bit of the lo mantissa is zero so we need to normalize
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it for the low double. Shift it left until the hidden bit is '1'
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then adjust the 2nd exponent accordingly. */
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if (sizeof (lo) == sizeof (long))
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lzcount = __builtin_clzl (lo);
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else if ((lo >> 32) != 0)
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lzcount = __builtin_clzl ((long) (lo >> 32));
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else
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lzcount = __builtin_clzl ((long) lo) + 32;
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lzcount = lzcount - 11;
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if (lzcount > 0)
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{
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lo = lo << lzcount;
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u.ieee.exponent2 = u.ieee.exponent2 - lzcount;
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}
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}
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else
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{
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u.ieee.negative2 = 0;
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u.ieee.exponent2 = 0;
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}
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u.ieee.mantissa3 = lo & 0xffffffffLL;
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u.ieee.mantissa2 = (lo >> 32) & 0xffffff;
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u.ieee.mantissa1 = hi & 0xffffffffLL;
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u.ieee.mantissa0 = (hi >> 32) & ((1LL << (LDBL_MANT_DIG - 86)) - 1);
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return u.d;
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}
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