efee5258bc
The MPFR library is a C library for multiple-precision floating-point computations with exact rounding (also called correct rounding). It is based on the GMP multiple-precision library and should replace the MPF class in further releases of GMP. GCC >= 4.2 requires MPFR.
62 lines
1.7 KiB
C
62 lines
1.7 KiB
C
/* mpfr_min_prec -- minimal size in bits to hold the mantissa
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Copyright 2009, 2010, 2011 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 "mpfr-impl.h"
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mpfr_prec_t
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mpfr_min_prec (mpfr_srcptr x)
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{
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mp_limb_t *mx;
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mpfr_prec_t px, res;
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mp_size_t n;
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int i;
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if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (x)))
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return 0;
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mx = MPFR_MANT (x);
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px = MPFR_PREC (x);
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res = 0;
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/* Count full limbs set to zero */
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for (n = 0; mx[n] == 0; n++)
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{
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res += GMP_NUMB_BITS;
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}
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i = 0;
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/* mx[n] is now the first limb which is not null. Count number
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* of null bits in mx[n], from the right */
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while ((mx[n] & (MPFR_LIMB_ONE << i)) == 0)
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i++;
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res += i;
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/* If we have trailing zero bits because the precision
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* is not a multiple of GMP_NUMB_BITS, we must not count
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* those. */
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i = px % GMP_NUMB_BITS;
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if (i != 0)
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res -= GMP_NUMB_BITS - i;
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return px - res;
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}
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