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Only use the fast-div test for the first number in the chain because it skips fractional length calculation, thus preventing a potential block! Thanks to mtrlt for spotting this.

master
mikaelh 2013-07-25 10:46:41 +03:00
parent c226dcd5af
commit 59625e36d7
1 changed files with 4 additions and 22 deletions
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26
src/prime.cpp
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@ -554,7 +554,7 @@ static bool FermatProbablePrimalityTestFast(const mpz_class& n, unsigned int& nL
for (; nPrimeSeq < nPrimeSeqEnd; nPrimeSeq++)
{
if (lRemainder % vPrimes[nPrimeSeq] == 0)
return false;
return false; // returning here skips the fractional length calculation!
}
}
}
@ -583,31 +583,13 @@ static bool FermatProbablePrimalityTestFast(const mpz_class& n, unsigned int& nL
// Return values
// true: n is probable prime
// false: n is composite; set fractional length in the nLength output
static bool EulerLagrangeLifchitzPrimalityTestFast(const mpz_class& n, bool fSophieGermain, unsigned int& nLength, CPrimalityTestParams& testParams, bool fFastDiv = false)
static bool EulerLagrangeLifchitzPrimalityTestFast(const mpz_class& n, bool fSophieGermain, unsigned int& nLength, CPrimalityTestParams& testParams)
{
// Faster GMP version
mpz_t& mpzE = testParams.mpzE;
mpz_t& mpzR = testParams.mpzR;
mpz_t& mpzRplusOne = testParams.mpzRplusOne;
if (fFastDiv)
{
// Fast divisibility tests
// Divide n by a large divisor
// Use the remainder to test divisibility by small primes
const unsigned int nDivSize = testParams.nFastDivisorsSize;
for (unsigned int i = 0; i < nDivSize; i++)
{
unsigned long lRemainder = mpz_tdiv_ui(n.get_mpz_t(), testParams.vFastDivisors[i]);
unsigned int nPrimeSeq = testParams.vFastDivSeq[i];
const unsigned int nPrimeSeqEnd = testParams.vFastDivSeq[i + 1];
for (; nPrimeSeq < nPrimeSeqEnd; nPrimeSeq++)
{
if (lRemainder % vPrimes[nPrimeSeq] == 0)
return false;
}
}
}
mpz_sub_ui(mpzE, n.get_mpz_t(), 1);
mpz_tdiv_q_2exp(mpzE, mpzE, 1);
mpz_powm(mpzR, mpzTwo.get_mpz_t(), mpzE, n.get_mpz_t());
@ -675,12 +657,12 @@ static bool ProbableCunninghamChainTestFast(const mpz_class& n, bool fSophieGerm
N += (fSophieGermain? 1 : (-1));
if (fFermatTest)
{
if (!FermatProbablePrimalityTestFast(N, nProbableChainLength, testParams, true))
if (!FermatProbablePrimalityTestFast(N, nProbableChainLength, testParams))
break;
}
else
{
if (!EulerLagrangeLifchitzPrimalityTestFast(N, fSophieGermain, nProbableChainLength, testParams, true))
if (!EulerLagrangeLifchitzPrimalityTestFast(N, fSophieGermain, nProbableChainLength, testParams))
break;
}
}