113 lines
2.9 KiB
C
113 lines
2.9 KiB
C
/*============================================================================
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This file is part of FLINT.
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FLINT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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FLINT 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
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with FLINT; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2012 Fredrik Johansson
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******************************************************************************/
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#include <gmp.h>
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#include "flint.h"
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#include "ulong_extras.h"
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#include "fmpz.h"
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mp_limb_t
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fmpz_abs_ubound_ui_2exp(slong * exp, const fmpz_t x, int bits)
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{
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mp_limb_t m;
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slong shift, e, size;
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fmpz c = *x;
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if (!COEFF_IS_MPZ(c))
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{
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m = FLINT_ABS(c);
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e = 0;
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}
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else
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{
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/* mpz */
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__mpz_struct * z = COEFF_TO_PTR(c);
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size = z->_mp_size;
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size = FLINT_ABS(size);
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e = (size - 1) * FLINT_BITS;
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if (size == 1)
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{
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m = z->_mp_d[0];
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}
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else /* there are two or more limbs */
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{
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/* top limb (which must be nonzero) */
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m = z->_mp_d[size - 1];
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count_leading_zeros(shift, m);
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shift = FLINT_BITS - shift - bits;
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e += shift;
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if (shift >= 0)
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{
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/* round up */
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m = (m >> shift) + 1;
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}
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else
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{
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/* read a second limb to get an accurate value */
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mp_limb_t m2 = z->_mp_d[size - 2];
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m = (m << (-shift)) | (m2 >> (FLINT_BITS + shift));
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/* round up */
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m++;
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}
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/* adding 1 caused overflow to the next power of two */
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if ((m & (m - UWORD(1))) == UWORD(0))
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{
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m = UWORD(1) << (bits - 1);
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e++;
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}
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*exp = e;
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return m;
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}
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}
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/* single limb, adjust */
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count_leading_zeros(shift, m);
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e = FLINT_BITS - shift - bits;
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if (e >= 0)
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{
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m = (m >> e) + 1;
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/* overflowed to next power of two */
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if ((m & (m - 1)) == UWORD(0))
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{
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m = UWORD(1) << (bits - 1);
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e++;
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}
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}
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else
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{
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m <<= (-e);
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}
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*exp = e;
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return m;
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}
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