div.c
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上传日期:2022-08-06
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- /* mpf_div -- Divide two floats.
- Copyright 1993, 1994, 1996, 2000, 2001, 2002, 2004, 2005, 2010 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"
- /* Not done:
- No attempt is made to identify an overlap u==v. The result will be
- correct (1.0), but a full actual division is done whereas of course
- x/x==1 needs no work. Such a call is not a sensible thing to make, and
- it's left to an application to notice and optimize if it might arise
- somehow through pointer aliasing or whatever.
- Enhancements:
- The high quotient limb is non-zero when high{up,vsize} >= {vp,vsize}. We
- could make that comparison and use qsize==prec instead of qsize==prec+1,
- to save one limb in the division.
- If r==u but the size is enough bigger than prec that there won't be an
- overlap between quotient and dividend in mpn_tdiv_qr, then we can avoid
- copying up,usize. This would only arise from a prec reduced with
- mpf_set_prec_raw and will be pretty unusual, but might be worthwhile if
- it could be worked into the copy_u decision cleanly. */
- void
- mpf_div (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
- {
- mp_srcptr up, vp;
- mp_ptr rp, tp, new_vp;
- mp_size_t usize, vsize, rsize, prospective_rsize, tsize, zeros;
- mp_size_t sign_quotient, prec, high_zero, chop;
- mp_exp_t rexp;
- int copy_u;
- TMP_DECL;
- usize = SIZ(u);
- vsize = SIZ(v);
- sign_quotient = usize ^ vsize;
- usize = ABS (usize);
- vsize = ABS (vsize);
- prec = PREC(r);
- if (vsize == 0)
- DIVIDE_BY_ZERO;
- if (usize == 0)
- {
- SIZ(r) = 0;
- EXP(r) = 0;
- return;
- }
- TMP_MARK;
- rexp = EXP(u) - EXP(v) + 1;
- rp = PTR(r);
- up = PTR(u);
- vp = PTR(v);
- prospective_rsize = usize - vsize + 1; /* quot from using given u,v sizes */
- rsize = prec + 1; /* desired quot */
- zeros = rsize - prospective_rsize; /* padding u to give rsize */
- copy_u = (zeros > 0 || rp == up); /* copy u if overlap or padding */
- chop = MAX (-zeros, 0); /* negative zeros means shorten u */
- up += chop;
- usize -= chop;
- zeros += chop; /* now zeros >= 0 */
- tsize = usize + zeros; /* size for possible copy of u */
- /* copy and possibly extend u if necessary */
- if (copy_u)
- {
- tp = TMP_ALLOC_LIMBS (tsize + 1); /* +1 for mpn_div_q's scratch needs */
- MPN_ZERO (tp, zeros);
- MPN_COPY (tp+zeros, up, usize);
- up = tp;
- usize = tsize;
- }
- else
- {
- tp = TMP_ALLOC_LIMBS (usize + 1);
- }
- /* ensure divisor doesn't overlap quotient */
- if (rp == vp)
- {
- new_vp = TMP_ALLOC_LIMBS (vsize);
- MPN_COPY (new_vp, vp, vsize);
- vp = new_vp;
- }
- ASSERT (usize-vsize+1 == rsize);
- mpn_div_q (rp, up, usize, vp, vsize, tp);
- /* strip possible zero high limb */
- high_zero = (rp[rsize-1] == 0);
- rsize -= high_zero;
- rexp -= high_zero;
- SIZ(r) = sign_quotient >= 0 ? rsize : -rsize;
- EXP(r) = rexp;
- TMP_FREE;
- }