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put more realistic trial division limit in next_likely_prime

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This commit is contained in:
jasonmoxham 2009-10-12 13:10:09 +00:00
parent 07bbd31e1d
commit 51132cb0e3
1 changed files with 6 additions and 4 deletions
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10
mpz/likely_prime_p.c
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@ -31,6 +31,7 @@ int
mpz_likely_prime_p (mpz_srcptr N, gmp_randstate_t STATE, unsigned long td)
{
int d, t, r;
unsigned long tdlim;
mpz_t base, nm1, x, e, n;
ALLOC (n) = ALLOC (N);
@ -46,13 +47,14 @@ mpz_likely_prime_p (mpz_srcptr N, gmp_randstate_t STATE, unsigned long td)
// therefore it has a good chance of factoring by small divisiors , so try trial division as its fast and it checks small divisors
// checking for other divisors is not worth it even if the test is fast as we have random integer so only small divisors are common
// enough , remember this is not exact so it doesn't matter if we miss a few divisors
#define LIM 257
d=mpz_trial_division(n,3,LIM);
tdlim=mpz_sizeinbase(n,2);
tdlim=MAX(1000,tdlim);
d=mpz_trial_division(n,3,tdlim);
if(d!=0)
{if(mpz_cmp_ui(n, d) == 0)return 1;
return 0;}
if (mpz_cmp_ui (n, LIM * LIM) < 0)
return 1;
if (mpz_cmp_ui (n, tdlim * tdlim) < 0)
return 1; // if tdlim*tdlim overflows then n is not a single limb so cant be true anyway
ASSERT (mpz_odd_p (n));
ASSERT (mpz_cmp_ui (n, 5) >= 0); // so we can choose a base
// now do strong pseudoprime test