149 lines
4.4 KiB
C
149 lines
4.4 KiB
C
/* mpf_div -- Divide two floats.
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Copyright 1993, 1994, 1996, 2000, 2001, 2002, 2004, 2005 Free Software
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Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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MA 02110-1301, USA. */
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#include <stdio.h> /* for NULL */
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#include "gmp.h"
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#include "gmp-impl.h"
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#include "longlong.h"
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/* Not done:
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No attempt is made to identify an overlap u==v. The result will be
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correct (1.0), but a full actual division is done whereas of course
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x/x==1 needs no work. Such a call is not a sensible thing to make, and
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it's left to an application to notice and optimize if it might arise
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somehow through pointer aliasing or whatever.
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Enhancements:
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The high quotient limb is non-zero when high{up,vsize} >= {vp,vsize}. We
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could make that comparison and use qsize==prec instead of qsize==prec+1,
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to save one limb in the division.
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If r==u but the size is enough bigger than prec that there won't be an
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overlap between quotient and dividend in mpn_tdiv_qr, then we can avoid
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copying up,usize. This would only arise from a prec reduced with
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mpf_set_prec_raw and will be pretty unusual, but might be worthwhile if
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it could be worked into the copy_u decision cleanly.
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Future:
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If/when mpn_tdiv_qr supports its qxn parameter we can use that instead of
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padding u with zeros in temporary space.
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If/when a quotient-only division exists it can be used here immediately.
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remp is only to satisfy mpn_tdiv_qr, the remainder is not used. */
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void
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mpf_div (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
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{
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mp_srcptr up, vp;
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mp_ptr rp, remp, tp, new_vp;
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mp_size_t usize, vsize, rsize, prospective_rsize, tsize, zeros, copy_v_size;
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mp_size_t sign_quotient, prec, high_zero, chop;
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mp_exp_t rexp;
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int copy_u;
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TMP_DECL;
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usize = u->_mp_size;
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vsize = v->_mp_size;
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sign_quotient = usize ^ vsize;
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usize = ABS (usize);
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vsize = ABS (vsize);
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prec = r->_mp_prec;
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if (vsize == 0)
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DIVIDE_BY_ZERO;
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if (usize == 0)
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{
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r->_mp_size = 0;
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r->_mp_exp = 0;
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return;
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}
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TMP_MARK;
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rexp = u->_mp_exp - v->_mp_exp + 1;
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rp = r->_mp_d;
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up = u->_mp_d;
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vp = v->_mp_d;
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prospective_rsize = usize - vsize + 1; /* quot from using given u,v sizes */
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rsize = prec + 1; /* desired quot */
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zeros = rsize - prospective_rsize; /* padding u to give rsize */
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copy_u = (zeros > 0 || rp == up); /* copy u if overlap or padding */
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chop = MAX (-zeros, 0); /* negative zeros means shorten u */
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up += chop;
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usize -= chop;
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zeros += chop; /* now zeros >= 0 */
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tsize = usize + zeros; /* size for possible copy of u */
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if (WANT_TMP_DEBUG)
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{
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/* separate blocks, for malloc debugging */
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remp = TMP_ALLOC_LIMBS (vsize);
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tp = (copy_u ? TMP_ALLOC_LIMBS (tsize) : NULL);
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new_vp = (rp == vp ? TMP_ALLOC_LIMBS (vsize) : NULL);
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}
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else
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{
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/* one block with conditionalized size, for efficiency */
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copy_v_size = (rp == vp ? vsize : 0);
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remp = TMP_ALLOC_LIMBS (vsize + copy_v_size + (copy_u ? tsize : 0));
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new_vp = remp + vsize;
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tp = new_vp + copy_v_size;
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}
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/* copy and possibly extend u if necessary */
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if (copy_u)
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{
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MPN_ZERO (tp, zeros);
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MPN_COPY (tp+zeros, up, usize);
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up = tp;
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usize = tsize;
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}
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/* ensure divisor doesn't overlap quotient */
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if (rp == vp)
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{
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MPN_COPY (new_vp, vp, vsize);
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vp = new_vp;
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}
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ASSERT (usize-vsize+1 == rsize);
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mpn_tdiv_qr (rp, remp, (mp_size_t) 0, up, usize, vp, vsize);
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/* strip possible zero high limb */
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high_zero = (rp[rsize-1] == 0);
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rsize -= high_zero;
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rexp -= high_zero;
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r->_mp_size = sign_quotient >= 0 ? rsize : -rsize;
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r->_mp_exp = rexp;
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TMP_FREE;
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}
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