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tprobably_prime: run more than one Miller-Rabin round - plan9port - [fork] Plan… |
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git clone git://src.adamsgaard.dk/plan9port |
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--- |
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commit 1619f52cbc2096dd2fc93b189890bc8fd0771681 |
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parent a1afc8529d03515d361110edcabb73402527be89 |
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Author: Russ Cox <[email protected]> |
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Date: Thu, 11 Mar 2010 18:04:42 -0800 |
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probably_prime: run more than one Miller-Rabin round |
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R=rsc |
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http://codereview.appspot.com/462041 |
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Diffstat: |
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M src/libsec/port/probably_prime.c | 29 +++++++++++++++++------------ |
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1 file changed, 17 insertions(+), 12 deletions(-) |
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--- |
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diff --git a/src/libsec/port/probably_prime.c b/src/libsec/port/probably_prime.c |
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t@@ -9,7 +9,7 @@ |
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int |
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probably_prime(mpint *n, int nrep) |
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{ |
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- int j, k, rep, nbits, isprime = 1; |
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+ int j, k, rep, nbits, isprime; |
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mpint *nm1, *q, *x, *y, *r; |
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if(n->sign < 0) |
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t@@ -49,32 +49,37 @@ probably_prime(mpint *n, int nrep) |
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mpright(nm1, k, q); /* q = (n-1)/2**k */ |
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for(rep = 0; rep < nrep; rep++){ |
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- |
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- /* x = random in [2, n-2] */ |
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- r = mprand(nbits, prng, nil); |
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- mpmod(r, nm1, x); |
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- mpfree(r); |
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- if(mpcmp(x, mpone) <= 0) |
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- continue; |
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+ for(;;){ |
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+ /* find x = random in [2, n-2] */ |
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+ r = mprand(nbits, prng, nil); |
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+ mpmod(r, nm1, x); |
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+ mpfree(r); |
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+ if(mpcmp(x, mpone) > 0) |
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+ break; |
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+ } |
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/* y = x**q mod n */ |
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mpexp(x, q, n, y); |
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if(mpcmp(y, mpone) == 0 || mpcmp(y, nm1) == 0) |
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- goto done; |
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+ continue; |
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- for(j = 1; j < k; j++){ |
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+ for(j = 1;; j++){ |
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+ if(j >= k) { |
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+ isprime = 0; |
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+ goto done; |
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+ } |
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mpmul(y, y, x); |
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mpmod(x, n, y); /* y = y*y mod n */ |
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if(mpcmp(y, nm1) == 0) |
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- goto done; |
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+ break; |
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if(mpcmp(y, mpone) == 0){ |
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isprime = 0; |
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goto done; |
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} |
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} |
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- isprime = 0; |
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} |
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+ isprime = 1; |
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done: |
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mpfree(y); |
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mpfree(x); |
