45 lines
1.5 KiB
C
45 lines
1.5 KiB
C
|
/* mpn_divexact_by exact division by (B-1)/f
|
||
|
|
|
||
|
|
Copyright 2009 Jason Moxham
|
||
|
|
|
||
|
|
This file is part of the MPIR Library.
|
||
|
|
|
||
|
|
The MPIR 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 2.1 of the License, or (at
|
||
|
|
your option) any later version.
|
||
|
|
|
||
|
|
The MPIR 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 MPIR Library; see the file COPYING.LIB. If not, write
|
||
|
|
to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
|
||
|
|
Boston, MA 02110-1301, USA.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include "mpir.h"
|
||
|
|
#include "gmp-impl.h"
|
||
|
|
#include "longlong.h"
|
||
|
|
|
||
|
|
mp_limb_t mpn_divexact_byBm1of(mp_ptr qp,mp_srcptr xp,mp_size_t n,mp_limb_t f,mp_limb_t Bm1of)
|
||
|
|
{mp_size_t j;mp_limb_t c,acc,ax,dx;
|
||
|
|
|
||
|
|
ASSERT(n>0);
|
||
|
|
ASSERT_MPN(xp,n);
|
||
|
|
ASSERT(MPN_SAME_OR_SEPARATE_P(qp,xp,n));
|
||
|
|
ASSERT(Bm1of*f+1==0);
|
||
|
|
acc=0*Bm1of;// carry in is 0
|
||
|
|
for(j=0;j<=n-1;j++)
|
||
|
|
{umul_ppmm(dx,ax,xp[j],Bm1of);
|
||
|
|
SUBC_LIMB(c,acc,acc,ax);
|
||
|
|
qp[j]=acc;
|
||
|
|
acc-=dx+c;}
|
||
|
|
// return next quotient*-f
|
||
|
|
// we could save this mul here , we dont really need it , just left in for mathematical clarity
|
||
|
|
return acc*-f;} // so (xp,n) = (qp,n)*f -ret*B^n and 0 <= ret < f
|
||
|
|
|
||
|
|
// Note the divexact_by3 code is just a special case of this
|