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FXY.cc
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FXY.cc
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// Percy++ Copyright 2007,2012 Ian Goldberg <iang@cs.uwaterloo.ca>,
// Casey Devet <cjdevet@cs.uwaterloo.ca>,
// Paul Hendry <pshdenry@uwaterloo.ca>,
// Ryan Henry <rhenry@cs.uwaterloo.ca>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of version 2 of the GNU General Public License as
// published by the Free Software Foundation.
//
// This program 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 General Public License for more details.
//
// There is a copy of the GNU General Public License in the COPYING file
// packaged with this plugin; if you cannot find it, write to the Free
// Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
// 02110-1301 USA
#include "FXY.h"
NTL_OPEN_NNS
ZZ comb(long n, long k)
{
//
// compute binomial coefficients
//
// comb(n,k) = n! / k!(n-k)!
//
if( k==0 ) return to_ZZ(1);
if( k==1 ) return to_ZZ(n);
ZZ ONE = to_ZZ(1);
ZZ N = to_ZZ(n);
ZZ K = to_ZZ(k);
ZZ c = to_ZZ(1);
if( k < n-k ){
for(ZZ i = N; i >= N-K+ONE; i--){
c = ((c*i) / (N-i+ONE));
}
}else{
for(ZZ i = N; i >= K+ONE; i--){
c = ((c*i) / (N-i+ONE));
}
} // if-then-else
return c;
}
NTL_CLOSE_NNS