set_prc.c
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上传日期:2022-08-06
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- /* mpf_set_prec(x) -- Change the precision of x.
- Copyright 1993, 1994, 1995, 2000, 2001 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"
- /* A full new_prec+1 limbs are always retained, even though just new_prec
- would satisfy the requested precision. If size==new_prec+1 then
- certainly new_prec+1 should be kept since no copying is needed in that
- case. If just new_prec was kept for size>new_prec+1 it'd be a bit
- inconsistent. */
- void
- mpf_set_prec (mpf_ptr x, mp_bitcnt_t new_prec_in_bits)
- {
- mp_size_t old_prec, new_prec, new_prec_plus1;
- mp_size_t size, sign;
- mp_ptr xp;
- new_prec = __GMPF_BITS_TO_PREC (new_prec_in_bits);
- old_prec = PREC(x);
- /* do nothing if already the right precision */
- if (new_prec == old_prec)
- return;
- PREC(x) = new_prec;
- new_prec_plus1 = new_prec + 1;
- /* retain most significant limbs */
- sign = SIZ(x);
- size = ABS (sign);
- xp = PTR(x);
- if (size > new_prec_plus1)
- {
- SIZ(x) = (sign >= 0 ? new_prec_plus1 : -new_prec_plus1);
- MPN_COPY_INCR (xp, xp + size - new_prec_plus1, new_prec_plus1);
- }
- PTR(x) = __GMP_REALLOCATE_FUNC_LIMBS (xp, old_prec+1, new_prec_plus1);
- }