zmodn

commit 8ca27427af98bd3a82e8c5f4a199513295747930
parent 771667c2bb52235d6dacf67eab933207b59e167b
Author: Sebastiano Tronto <sebastiano@tronto.net>
Date:   Sat, 21 Dec 2024 18:13:27 +0100

Revert "Fix division"
Actually you cannot do division like that, the result is not unique.

This reverts commit 771667c2bb52235d6dacf67eab933207b59e167b.

Diffstat:
M
test
 | 
10
----------
M
zmodn.h
 | 
8
+++-----

2 files changed, 3 insertions(+), 15 deletions(-)
diff --git a/test b/test
@@ -141,16 +141,6 @@ public:
 		assert_equal(p, 92);
 	}
 },
-{
-	.name = "4 / 2 mod 6",
-	.f = []() {
-		Zmod<6> four = 4;
-		Zmod<6> two = 2;
-		auto d = four / two;
-		assert_equal(d.has_value(), true);
-		assert_equal(d.value(), 2);
-	}
-},
 };
 
 int main() {
diff --git a/zmodn.h b/zmodn.h
@@ -40,15 +40,13 @@ public:
 	bool operator!=(const Zmod& z) const { return value != z.value; }
 
 	std::optional<Zmod> inverse() const {
-		auto [g, a, b] = extended_gcd(value, N);
+		auto [g, a, _] = extended_gcd(value, N);
 		return g == 1 ? Zmod(a) : std::optional<Zmod>{};
 	}
 
 	std::optional<Zmod> operator/(const Zmod& d) const {
-		auto [g, x, y] = extended_gcd(value, d.toint());
-		auto [a, b] = std::pair<Zmod, Zmod>{value / g, d.toint() / g};
-		auto i = b.inverse();
-		return i ? a * i.value() : i;
+		auto i = d.inverse();
+		return i ? (*this) * i.value() : i;
 	}
 
 	std::optional<Zmod> operator/=(const Zmod& d) {