41 lines
1.5 KiB
C
41 lines
1.5 KiB
C
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/*
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Copyright 2009 Jason Moxham
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This file is part of the MPIR Library.
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The MPIR 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
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by the Free Software Foundation; either version 2.1 of the License, or (at
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your option) any later version.
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The MPIR 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 MPIR Library; see the file COPYING.LIB. If not, write
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to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
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Boston, MA 02110-1301, USA.
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*/
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#include "mpir.h"
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#include "gmp-impl.h"
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// returns smallest d such that d|N start <= d < stop d!=1 , if no such d exists return 0
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// the name trial_division implies a method , perhaps call it mpz_smallest_divisor
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// N must have no divisors <start
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unsigned long mpz_trial_division(mpz_srcptr N,unsigned long start,unsigned long stop)
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{unsigned long i,dd;
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//ASSERT N has no divisors <start excluding 1
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if(start<=2 && 2<stop && mpz_even_p(N))return 2;
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if(start<=3 && 3<stop && mpz_divisible_ui_p(N,3))return 3;
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if(start<5)start=5;// dont be daft
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if(start%2==0)start+=1;
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if(start%3==0)start+=2;
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ASSERT(start%2!=0);ASSERT(start%3!=0);
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dd=2;if(start%6==1)dd=4;
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for(i=start;i<stop;i+=dd,dd=6-dd)if(mpz_divisible_ui_p(N,i))return i;
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return 0;}
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