Commit ffb7aa8

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fix #149: improve barret algorithm

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+26

-5

lines changed

+26

-5

lines changed

Lines changed: 3 additions & 4 deletions

Original file line number	Diff line number	Diff line change
`@@ -26,7 +26,7 @@ struct barrett {`
`26`	`26`	`unsigned int _m;`
`27`	`27`	`unsigned long long im;`
`28`	`28`
`29`		- // @param m `1 <= m < 2^31`
	`29`	+ // @param m `1 <= m`
`30`	`30`	`explicit barrett(unsigned int m) : _m(m), im((unsigned long long)(-1) / m + 1) {}`
`31`	`31`
`32`	`32`	`// @return m`
`@@ -55,9 +55,8 @@ struct barrett {`
`55`	`55`	`unsigned long long x =`
`56`	`56`	`(unsigned long long)(((unsigned __int128)(z)*im) >> 64);`
`57`	`57`	`#endif`
`58`		`- unsigned int v = (unsigned int)(z - x * _m);`
`59`		`- if (_m <= v) v += _m;`
`60`		`- return v;`
	`58`	`+ unsigned long long y = x * _m;`
	`59`	`+ return (unsigned int)(z - y + (z < y ? _m : 0));`
`61`	`60`	`}`
`62`	`61`	`};`
`63`	`62`

Lines changed: 23 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -56,7 +56,7 @@ TEST(InternalMathTest, Barrett) {`
`56`	`56`	`ASSERT_EQ(0, bt.mul(0, 0));`
`57`	`57`	`}`
`58`	`58`
`59`		`-TEST(InternalMathTest, BarrettBorder) {`
	`59`	`+TEST(InternalMathTest, BarrettIntBorder) {`
`60`	`60`	`const int mod_upper = std::numeric_limits<int>::max();`
`61`	`61`	`for (unsigned int mod = mod_upper; mod >= mod_upper - 20; mod--) {`
`62`	`62`	`internal::barrett bt(mod);`
`@@ -78,6 +78,28 @@ TEST(InternalMathTest, BarrettBorder) {`
`78`	`78`	`}`
`79`	`79`	`}`
`80`	`80`
	`81`	`+TEST(InternalMathTest, BarrettUintBorder) {`
	`82`	`+ const unsigned int mod_upper = std::numeric_limits<unsigned int>::max();`
	`83`	`+ for (unsigned int mod = mod_upper; mod >= mod_upper - 20; mod--) {`
	`84`	`+ internal::barrett bt(mod);`
	`85`	`+ std::vector<unsigned int> v;`
	`86`	`+ for (int i = 0; i < 10; i++) {`
	`87`	`+ v.push_back(i);`
	`88`	`+ v.push_back(mod - i);`
	`89`	`+ v.push_back(mod / 2 + i);`
	`90`	`+ v.push_back(mod / 2 - i);`
	`91`	`+ }`
	`92`	`+ for (auto a : v) {`
	`93`	`+ ull a2 = a;`
	`94`	`+ ASSERT_EQ(((a2 * a2) % mod * a2) % mod, bt.mul(a, bt.mul(a, a)));`
	`95`	`+ for (auto b : v) {`
	`96`	`+ ull b2 = b;`
	`97`	`+ ASSERT_EQ((a2 * b2) % mod, bt.mul(a, b));`
	`98`	`+ }`
	`99`	`+ }`
	`100`	`+ }`
	`101`	`+}`
	`102`	`+`
`81`	`103`	`TEST(InternalMathTest, IsPrime) {`
`82`	`104`	`ASSERT_FALSE(internal::is_prime<121>);`
`83`	`105`	`ASSERT_FALSE(internal::is_prime<11 * 13>);`

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