223 lines
6.3 KiB
C
223 lines
6.3 KiB
C
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/*=============================================================================
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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) 2010 William Hart
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******************************************************************************/
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#include <gmp.h>
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#include "flint.h"
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#include "fmpz.h"
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int
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fmpz_bit_unpack(fmpz_t coeff, mp_srcptr arr, mp_bitcnt_t shift,
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mp_bitcnt_t bits, int negate, int borrow)
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{
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mp_limb_t mask, sign;
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ulong limbs = (shift + bits) / FLINT_BITS;
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ulong rem_bits = (shift + bits) % FLINT_BITS;
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/* determine if field is positive or negative */
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if (rem_bits)
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sign = ((((mp_limb_t) 1) << (rem_bits - 1)) & arr[limbs]);
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else
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sign = ((((mp_limb_t) 1) << (FLINT_BITS - 1)) & arr[limbs - 1]);
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if (bits <= FLINT_BITS - 2) /* fits into a small coeff */
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{
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_fmpz_demote(coeff);
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/* mask for the given number of bits */
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mask = (((mp_limb_t) 1) << bits) - (mp_limb_t) 1;
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if (limbs + (rem_bits != 0) > 1) /* field crosses a limb boundary */
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(*coeff) =
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((arr[0] >> shift) + (arr[1] << (FLINT_BITS - shift))) & mask;
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else /* field is in first limb only, mask it */
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(*coeff) = (arr[0] >> shift) & mask;
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/* sign extend */
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if (sign)
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(*coeff) += ((~(mp_limb_t) 0) << bits);
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/* determine whether we need to return a borrow */
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sign = (*coeff < (mp_limb_signed_t) 0 ? (mp_limb_t) 1 : (mp_limb_t) 0);
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/* deal with borrow */
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if (borrow)
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{
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(*coeff)++;
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if ((*coeff) > COEFF_MAX)
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{
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fmpz v = *coeff;
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*coeff = 0;
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fmpz_set_ui(coeff, v);
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}
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}
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/* negate the coeff if necessary */
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if (negate)
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fmpz_neg(coeff, coeff);
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return (sign != (mp_limb_t) 0);
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}
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else /* large coefficient */
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{
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__mpz_struct * mpz_ptr;
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mp_limb_t * p;
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ulong l, b;
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mpz_ptr = _fmpz_promote(coeff);
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/* the number of limbs to hold the bitfield _including_ b extra bits */
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l = (bits - 1) / FLINT_BITS + 1;
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b = bits % FLINT_BITS;
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/* allocate space for l limbs only */
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mpz_realloc(mpz_ptr, l);
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p = mpz_ptr->_mp_d;
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/* shift in l limbs */
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if (shift)
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mpn_rshift(p, arr, l, shift);
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else
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flint_mpn_copyi(p, arr, l);
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/* shift in any rem_bits that weren't already shifted */
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if (limbs + (rem_bits != 0) > l)
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p[l - 1] += (arr[limbs] << (FLINT_BITS - shift));
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/* mask off the last limb, if not full */
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if (b)
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{
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mask = (((mp_limb_t) 1) << b) - (mp_limb_t) 1;
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p[l - 1] &= mask;
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}
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if (sign != (mp_limb_t) 0)
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{
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/* sign extend */
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if (b)
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p[l - 1] += ((~(mp_limb_t) 0) << b);
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/* negate */
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mpn_com_n(p, p, l);
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if (!borrow)
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mpn_add_1(p, p, l, 1);
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/* normalise */
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while (l && (p[l - 1] == (mp_limb_t) 0))
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l--;
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mpz_ptr->_mp_size = -l;
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sign = 1;
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}
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else
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{
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/* deal with borrow */
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if (borrow)
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mpn_add_1(p, p, l, 1);
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/* normalise */
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while (l && (p[l - 1] == (mp_limb_t) 0))
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l--;
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mpz_ptr->_mp_size = l;
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sign = 0;
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}
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/* negate if required */
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if (negate)
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mpz_neg(mpz_ptr, mpz_ptr);
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/* coeff may fit in a small */
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_fmpz_demote_val(coeff);
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return sign;
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}
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}
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void
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fmpz_bit_unpack_unsigned(fmpz_t coeff, mp_srcptr arr,
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mp_bitcnt_t shift, mp_bitcnt_t bits)
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{
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ulong limbs = (shift + bits) / FLINT_BITS;
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ulong rem_bits = (shift + bits) % FLINT_BITS;
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mp_limb_t mask;
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if (bits <= FLINT_BITS - 2) /* fits into a small coeff */
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{
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_fmpz_demote(coeff);
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/* mask for the given number of bits */
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mask = (((mp_limb_t) 1) << bits) - (mp_limb_t) 1;
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if (limbs + (rem_bits != 0) > 1) /* field crosses a limb boundary */
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(*coeff) =
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((arr[0] >> shift) + (arr[1] << (FLINT_BITS - shift))) & mask;
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else /* field is in first limb only, mask it */
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(*coeff) = (arr[0] >> shift) & mask;
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}
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else /* large coefficient */
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{
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__mpz_struct * mpz_ptr;
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mp_limb_t * p;
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ulong l, b;
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mpz_ptr = _fmpz_promote(coeff);
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/* the number of limbs to hold the bitfield _including_ b extra bits */
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l = (bits - 1) / FLINT_BITS + 1;
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b = bits % FLINT_BITS;
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/* allocate space for l limbs only */
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mpz_realloc(mpz_ptr, l);
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p = mpz_ptr->_mp_d;
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/* shift in l limbs */
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if (shift)
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mpn_rshift(p, arr, l, shift);
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else
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flint_mpn_copyi(p, arr, l);
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/* shift in any rem_bits that weren't already shifted */
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if (limbs + (rem_bits != 0) > l)
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p[l - 1] += (arr[limbs] << (FLINT_BITS - shift));
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/* mask off the last limb, if not full */
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if (b)
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{
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mask = (((mp_limb_t) 1) << b) - (mp_limb_t) 1;
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p[l - 1] &= mask;
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}
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/* normalise */
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while (l && (p[l - 1] == (mp_limb_t) 0))
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l--;
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mpz_ptr->_mp_size = l;
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/* coeff may fit in a small */
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_fmpz_demote_val(coeff);
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}
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}
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