Speed up integer-vector hashing

heyx3 · Jun 24, 2022 · 7bf0f75 · 7bf0f75
1 parent c4bf1b9
commit 7bf0f75
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Showing 3 changed files with 43 additions and 13 deletions.
diff --git a/WFC++/Vector2i.h b/WFC++/Vector2i.h
@@ -89,8 +89,13 @@ namespace WFC
 
 		Vector2i operator-() const { return Vector2i(-x, -y); }
 
-		bool operator==(const Vector2i& v) const { return (x == v.x) && (y == v.y); }
-		bool operator!=(const Vector2i& v) const { return (x != v.x) || (y != v.y); }
+		bool operator==(const Vector2i& v) const
+		{
+			static_assert(sizeof(Vector2i) == 2 * sizeof(int),
+						  "Vector2i has some byte padding");
+			return memcmp(this, &v, sizeof(Vector2i)) == 0;
+		}
+		bool operator!=(const Vector2i& v) const { return !operator==(v); }
 
 
 		Vector2i LessX() const { return Vector2i(x - 1, y); }
@@ -104,8 +109,19 @@ namespace WFC
 		//    assuming the "pivot" is halfway between the origin and "size".
 		Vector2i Transform(Transformations trnsf, Vector2i size) const;
 
-		uint32_t GetHashcode() const { return Math::Hash(static_cast<int32_t>(x),
-														 static_cast<int32_t>(y)); }
+		uint32_t GetHashcode() const
+		{
+			//This seems to be a significant bottleneck, so I spent some time thinking
+			//    and searching for a fast way to hash integers.
+			//Reference: https://stackoverflow.com/questions/30032950/creating-a-hash-seed-value-from-2-integers-fast
+			//It works better with high bits than low ones,
+			//    so I bitwise-invert the components before using them.
+			int a = ~x,
+				b = ~y;
+			a ^= b;
+			a = (a << 24) + (a * 0x193);
+			return a;
+		}
 	};
 
 

diff --git a/WFC++/Vector3i.h b/WFC++/Vector3i.h
@@ -55,8 +55,13 @@ namespace WFC
 
 		Vector3i operator-() const { return Vector3i(-x, -y, -z); }
 
-		bool operator==(const Vector3i& v) const { return (x == v.x) && (y == v.y) && (z == v.z); }
-		bool operator!=(const Vector3i& v) const { return (x != v.x) || (y != v.y) || (z != v.z); }
+		bool operator==(const Vector3i& v) const
+		{
+			static_assert(sizeof(Vector3i) == 3 * sizeof(int),
+						  "Vector3i has some byte padding");
+			return memcmp(this, &v, sizeof(Vector3i)) == 0;
+		}
+		bool operator!=(const Vector3i& v) const { return !operator==(v); }
 
 
 		Vector3i LessX() const { return Vector3i(x - 1, y, z); }
@@ -66,9 +71,10 @@ namespace WFC
         Vector3i LessZ() const { return Vector3i(x, y, z - 1); }
         Vector3i MoreZ() const { return Vector3i(x, y, z + 1); }
 
-		uint32_t GetHashcode() const { return Vector2i(static_cast<uint32_t>(z),
-				  							           Vector2i(x, y).GetHashcode()
-													  ).GetHashcode(); }
+		uint32_t GetHashcode() const
+		{
+			return Vector2i(Vector2i(x, y).GetHashcode(), z).GetHashcode();
+		}
 	};
 
 

diff --git a/WFC++/Vector4i.h b/WFC++/Vector4i.h
@@ -55,7 +55,12 @@ namespace WFC
 
 		Vector4i operator-() const { return Vector4i(-x, -y, -z, -w); }
 
-		bool operator==(const Vector4i& v) const { return (x == v.x) && (y == v.y) && (z == v.z) && (w == v.w); }
+		bool operator==(const Vector4i& v) const
+		{
+			static_assert(sizeof(Vector4i) == 4 * sizeof(int),
+						  "Vector4i has some byte padding");
+			return memcmp(this, &v, sizeof(Vector4i)) == 0;
+		}
 		bool operator!=(const Vector4i& v) const { return !operator==(v); }
 
 
@@ -68,9 +73,12 @@ namespace WFC
 		Vector4i LessW() const { return Vector4i(x, y, z, w - 1); }
 		Vector4i MoreW() const { return Vector4i(x, y, z, w + 1); }
 
-		uint32_t GetHashcode() const { return Vector2i(Vector2i(x, y).GetHashcode(),
-												       Vector2i(z, w).GetHashcode()
-													  ).GetHashcode(); }
+		uint32_t GetHashcode() const
+		{
+			auto a = Vector2i(x, y).GetHashcode(),
+				 b = Vector2i(x, y ).GetHashcode();
+			return Vector2i(static_cast<int32_t>(a), static_cast<int32_t>(b)).GetHashcode();
+		}
 	};