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Optimize GCD in pq_factorize.

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This commit is contained in:
levlam 2022-03-21 19:38:40 +03:00
parent cb155ebf1a
commit 93a2b9895d
1 changed files with 17 additions and 20 deletions
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37
tdutils/td/utils/crypto.cpp
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@ -55,42 +55,39 @@
namespace td { namespace td {
static uint64 gcd(uint64 a, uint64 b) { static uint64 pq_gcd(uint64 a, uint64 b) {
if (a == 0) { if (a == 0) {
return b; return b;
} }
if (b == 0) { while ((a & 1) == 0) {
return a;
}
int shift = 0;
while ((a & 1) == 0 && (b & 1) == 0) {
a >>= 1; a >>= 1;
b >>= 1;
shift++;
} }
DCHECK((b & 1) != 0);
while (true) { while (true) {
while ((a & 1) == 0) {
a >>= 1;
}
while ((b & 1) == 0) {
b >>= 1;
}
if (a > b) { if (a > b) {
a -= b; a = (a - b) >> 1;
while ((a & 1) == 0) {
a >>= 1;
}
} else if (b > a) { } else if (b > a) {
b -= a; b = (b - a) >> 1;
while ((b & 1) == 0) {
b >>= 1;
}
} else { } else {
return a << shift; return a;
} }
} }
} }
uint64 pq_factorize(uint64 pq) { uint64 pq_factorize(uint64 pq) {
if (pq < 2 || pq > (static_cast<uint64>(1) << 63)) { if (pq <= 2 || pq > (static_cast<uint64>(1) << 63)) {
return 1; return 1;
} }
if ((pq & 1) == 0) {
return 2;
}
uint64 g = 0; uint64 g = 0;
for (int i = 0, iter = 0; i < 3 || iter < 1000; i++) { for (int i = 0, iter = 0; i < 3 || iter < 1000; i++) {
uint64 q = Random::fast(17, 32) % (pq - 1); uint64 q = Random::fast(17, 32) % (pq - 1);
@ -120,7 +117,7 @@ uint64 pq_factorize(uint64 pq) {
x = c; x = c;
uint64 z = x < y ? pq + x - y : x - y; uint64 z = x < y ? pq + x - y : x - y;
g = gcd(z, pq); g = pq_gcd(z, pq);
if (g != 1) { if (g != 1) {
break; break;
} }