set_f.c
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上传日期:2022-08-06
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- /* mpq_set_f -- set an mpq from an mpf.
- Copyright 2000, 2001, 2002 Free Software Foundation, Inc.
- This file is part of the GNU MP Library.
- The GNU MP Library is free software; you can redistribute it and/or modify
- it under the terms of the GNU Lesser General Public License as published by
- the Free Software Foundation; either version 3 of the License, or (at your
- option) any later version.
- The GNU MP Library is distributed in the hope that it will be useful, but
- WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- License for more details.
- You should have received a copy of the GNU Lesser General Public License
- along with the GNU MP Library. If not, see http://www.gnu.org/licenses/. */
- #include "gmp.h"
- #include "gmp-impl.h"
- #include "longlong.h"
- void
- mpq_set_f (mpq_ptr q, mpf_srcptr f)
- {
- mp_size_t fexp = EXP(f);
- mp_ptr fptr = PTR(f);
- mp_size_t fsize = SIZ(f);
- mp_size_t abs_fsize = ABS(fsize);
- mp_limb_t flow;
- if (fsize == 0)
- {
- /* set q=0 */
- q->_mp_num._mp_size = 0;
- q->_mp_den._mp_size = 1;
- q->_mp_den._mp_d[0] = 1;
- return;
- }
- /* strip low zero limbs from f */
- flow = *fptr;
- MPN_STRIP_LOW_ZEROS_NOT_ZERO (fptr, abs_fsize, flow);
- if (fexp >= abs_fsize)
- {
- /* radix point is to the right of the limbs, no denominator */
- mp_ptr num_ptr;
- MPZ_REALLOC (mpq_numref (q), fexp);
- num_ptr = q->_mp_num._mp_d;
- MPN_ZERO (num_ptr, fexp - abs_fsize);
- MPN_COPY (num_ptr + fexp - abs_fsize, fptr, abs_fsize);
- q->_mp_num._mp_size = fsize >= 0 ? fexp : -fexp;
- q->_mp_den._mp_size = 1;
- q->_mp_den._mp_d[0] = 1;
- }
- else
- {
- /* radix point is within or to the left of the limbs, use denominator */
- mp_ptr num_ptr, den_ptr;
- mp_size_t den_size;
- den_size = abs_fsize - fexp;
- MPZ_REALLOC (mpq_numref (q), abs_fsize);
- MPZ_REALLOC (mpq_denref (q), den_size+1);
- num_ptr = q->_mp_num._mp_d;
- den_ptr = q->_mp_den._mp_d;
- if (flow & 1)
- {
- /* no powers of two to strip from numerator */
- MPN_COPY (num_ptr, fptr, abs_fsize);
- MPN_ZERO (den_ptr, den_size);
- den_ptr[den_size] = 1;
- }
- else
- {
- /* right shift numerator, adjust denominator accordingly */
- int shift;
- den_size--;
- count_trailing_zeros (shift, flow);
- mpn_rshift (num_ptr, fptr, abs_fsize, shift);
- abs_fsize -= (num_ptr[abs_fsize-1] == 0);
- MPN_ZERO (den_ptr, den_size);
- den_ptr[den_size] = GMP_LIMB_HIGHBIT >> (shift-1);
- }
- q->_mp_num._mp_size = fsize >= 0 ? abs_fsize : -abs_fsize;
- q->_mp_den._mp_size = den_size + 1;
- }
- }