replace divide and multiply with shifts

1 files changed, 16 insertions, 4 deletions

diff --git a/world.hpp b/world.hpp
index a45cf9c..f486ba1 100644
--- a/world.hpp
+++ b/world.hpp
@@ -16,6 +16,18 @@ using Entity_Id = uint32_t;
 #define max_components 64
 #define max_slinkies (max_entities / slinky_size)
 
+static_assert((!(slinky_size & (slinky_size - 1))));
+/* slinky_size needs to be a power of 2 */
+static consteval int get_slinky_size_bit() {
+	int i;
+	int m = slinky_size;
+	for (i = 0; m; m >>= 1, i++);
+	if (i == 0)
+		throw "wtf";
+	return i - 1;
+}
+static constexpr int slinky_size_bit = get_slinky_size_bit();
+
 struct Slinky {
 	Entity_Id* entities;
 	void* data;
@@ -142,9 +154,9 @@ struct World {
 			template <typename C>
 			C& get() {
 				Pool* p = v->pools[ind];
-				Slinky& s = p->slinkies[ptr / slinky_size];
+				Slinky& s = p->slinkies[ptr >> slinky_size_bit];
 				int si = &s - p->slinkies;
-				int off = ptr - (si * slinky_size);
+				int off = ptr - (si << slinky_size_bit);
 				return *(C*)(
 					(char*)s.data + off * p->size +
 					p->offsets[v->w->get_component_id<C>()]
@@ -157,9 +169,9 @@ struct World {
 
 			Entity_Id entity() {
 				Pool* p = v->pools[ind];
-				Slinky& s = p->slinkies[ptr / slinky_size];
+				Slinky& s = p->slinkies[ptr >> slinky_size_bit];
 				int si = &s - p->slinkies;
-				int off = ptr - (si * slinky_size);
+				int off = ptr - (si << slinky_size_bit);
 				return s.entities[off];
 			}
 		};