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b58ddff026
* merged mpfr 3.0.0 and gmp 5.0.1 in buildtools trunk git-svn-id: file:///srv/svn/repos/haiku/buildtools/trunk@37378 a95241bf-73f2-0310-859d-f6bbb57e9c96
124 lines
4.1 KiB
C
124 lines
4.1 KiB
C
/* mpfr_get_flt -- convert a mpfr_t to a machine single precision float
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Copyright 2009, 2010 Free Software Foundation, Inc.
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Contributed by the Arenaire and Cacao projects, INRIA.
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This file is part of the GNU MPFR Library.
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The GNU MPFR Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MPFR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
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http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
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51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
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#include <float.h> /* for FLT_MIN */
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#define MPFR_NEED_LONGLONG_H
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#include "mpfr-impl.h"
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#include "ieee_floats.h"
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#define FLT_NEG_ZERO ((float) DBL_NEG_ZERO)
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#define MPFR_FLT_INFM ((float) MPFR_DBL_INFM)
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#define MPFR_FLT_INFP ((float) MPFR_DBL_INFP)
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float
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mpfr_get_flt (mpfr_srcptr src, mpfr_rnd_t rnd_mode)
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{
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int negative;
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mpfr_exp_t e;
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float d;
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/* in case of NaN, +Inf, -Inf, +0, -0, the conversion from double to float
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is exact */
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if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (src)))
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return (float) mpfr_get_d (src, rnd_mode);
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e = MPFR_GET_EXP (src);
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negative = MPFR_IS_NEG (src);
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if (MPFR_UNLIKELY(rnd_mode == MPFR_RNDA))
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rnd_mode = negative ? MPFR_RNDD : MPFR_RNDU;
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/* the smallest positive normal float number is 2^(-126) = 0.5*2^(-125),
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and the smallest positive subnormal number is 2^(-149) = 0.5*2^(-148) */
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if (MPFR_UNLIKELY (e < -148))
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{
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/* |src| < 2^(-149), i.e., |src| is smaller than the smallest positive
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subnormal number.
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In round-to-nearest mode, 2^(-150) is rounded to zero.
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*/
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d = negative ?
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(rnd_mode == MPFR_RNDD ||
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(rnd_mode == MPFR_RNDN && mpfr_cmp_si_2exp (src, -1, -150) < 0)
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? -FLT_MIN : FLT_NEG_ZERO) :
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(rnd_mode == MPFR_RNDU ||
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(rnd_mode == MPFR_RNDN && mpfr_cmp_si_2exp (src, 1, -150) > 0)
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? FLT_MIN : 0.0);
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if (d != 0.0) /* we multiply FLT_MIN = 2^(-126) by FLT_EPSILON = 2^(-23)
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to get +-2^(-149) */
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d *= FLT_EPSILON;
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}
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/* the largest normal number is 2^128*(1-2^(-24)) = 0.111...111e128 */
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else if (MPFR_UNLIKELY (e > 128))
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{
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d = negative ?
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(rnd_mode == MPFR_RNDZ || rnd_mode == MPFR_RNDU ?
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-FLT_MAX : MPFR_FLT_INFM) :
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(rnd_mode == MPFR_RNDZ || rnd_mode == MPFR_RNDD ?
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FLT_MAX : MPFR_FLT_INFP);
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}
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else /* -148 <= e <= 127 */
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{
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int nbits;
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mp_size_t np, i;
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mp_limb_t tp[MPFR_LIMBS_PER_FLT];
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int carry;
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double dd;
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nbits = IEEE_FLT_MANT_DIG; /* 24 */
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if (MPFR_UNLIKELY (e < -125))
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/*In the subnormal case, compute the exact number of significant bits*/
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{
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nbits += (125 + e);
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MPFR_ASSERTD (nbits >= 1);
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}
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np = (nbits + GMP_NUMB_BITS - 1) / GMP_NUMB_BITS;
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MPFR_ASSERTD(np <= MPFR_LIMBS_PER_FLT);
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carry = mpfr_round_raw_4 (tp, MPFR_MANT(src), MPFR_PREC(src), negative,
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nbits, rnd_mode);
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/* we perform the reconstruction using the 'double' type here,
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knowing the result is exactly representable as 'float' */
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if (MPFR_UNLIKELY(carry))
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dd = 1.0;
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else
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{
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/* The following computations are exact thanks to the previous
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mpfr_round_raw. */
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dd = (double) tp[0] / MP_BASE_AS_DOUBLE;
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for (i = 1 ; i < np ; i++)
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dd = (dd + tp[i]) / MP_BASE_AS_DOUBLE;
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/* dd is the mantissa (between 1/2 and 1) of the argument rounded
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to 24 bits */
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}
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dd = mpfr_scale2 (dd, e);
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if (negative)
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dd = -dd;
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/* convert (exacly) to float */
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d = (float) dd;
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}
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return d;
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}
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