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/* mpf_div -- Divide two floats.
Copyright 1993, 1994, 1996, 2000-2002, 2004, 2005, 2010, 2012 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 https://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_div_q, 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);
if (UNLIKELY (vsize == 0))
DIVIDE_BY_ZERO;
if (usize == 0)
{
SIZ(r) = 0;
EXP(r) = 0;
return;
}
sign_quotient = usize ^ vsize;
usize = ABS (usize);
vsize = ABS (vsize);
prec = PREC(r);
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;
}
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