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Skip the fractional length calculation if the first primality test fails (as suggested by gatra on bitcointalk).

master
mikaelh 2013-07-24 12:31:24 +03:00
parent a51d63ea37
commit 64528eba38
1 changed files with 4 additions and 4 deletions
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8
src/prime.cpp
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@ -531,7 +531,7 @@ public:
// Check Fermat probable primality test (2-PRP): 2 ** (n-1) = 1 (mod n)
// true: n is probable prime
// false: n is composite; set fractional length in the nLength output
static bool FermatProbablePrimalityTestFast(const mpz_class& n, unsigned int& nLength, CPrimalityTestParams& testParams, bool fFastDiv = false)
static bool FermatProbablePrimalityTestFast(const mpz_class& n, unsigned int& nLength, CPrimalityTestParams& testParams, bool fFastDiv = false, bool fFastFail = false)
{
// Faster GMP version
mpz_t& mpzN = testParams.mpzN;
@ -556,9 +556,9 @@ static bool FermatProbablePrimalityTestFast(const mpz_class& n, unsigned int& nL
mpz_sub_ui(mpzE, mpzN, 1);
mpz_powm(mpzR, mpzTwo.get_mpz_t(), mpzE, mpzN);
if (mpz_cmp_ui(mpzR, 1) == 0)
{
return true;
}
if (fFastFail)
return false;
// Failed Fermat test, calculate fractional length
mpz_sub(mpzE, mpzN, mpzR);
mpz_mul_2exp(mpzR, mpzE, nFractionalBits);
@ -655,7 +655,7 @@ static bool ProbableCunninghamChainTestFast(const mpz_class& n, bool fSophieGerm
N = n;
// Fermat test for n first
if (!FermatProbablePrimalityTestFast(N, nProbableChainLength, testParams, true))
if (!FermatProbablePrimalityTestFast(N, nProbableChainLength, testParams, true, true))
return false;
// Euler-Lagrange-Lifchitz test for the following numbers in chain