fast log2

pkg/ecs/int-log.go

@@ -8,6 +8,10 @@ package ecs
 
 import "math/bits"
 
-func FastIntLog2(value uint) int {
-	return bits.Len(value) - 1
+func FastIntLog2(value uint64) int {
+	return bits.Len64(value) - 1
+}
+
+func FastestIntLog2(value uint64) int {
+	return bits.LeadingZeros64(value) ^ 63
 }

pkg/ecs/int-log_test.go

@@ -8,28 +8,45 @@ package ecs
 
 import (
 	"math"
+	"math/bits"
 	"testing"
 )
 
 func TestCalcIndex(t *testing.T) {
-	for i := 0; i <= 100_000_000; i++ {
-		value := i>>10 + 1
+	for i := uint64(0); i <= 100_000_000; i++ {
+		var value uint64 = i>>10 + 1
 		want := int(math.Log2(float64(value)))
-		have := FastIntLog2(uint(value))
+		want2 := int(bits.LeadingZeros64(value) ^ 63)
+		have := bits.Len64(value) - 1
 		if want != have {
 			t.Fatalf("i: %v, want: %v, got: %v", i, want, have)
 		}
+		if want2 != have {
+			t.Fatalf("i: %v, want: %v, got: %v", i, want2, have)
+		}
+	}
+}
+
+func BenchmarkFastestLog2(b *testing.B) {
+	var i uint64 = 1
+	for b.Loop() {
+		_ = FastestIntLog2(i/10 + 1)
+		i++
 	}
 }
 
-func BenchmarkFastLog2(t *testing.B) {
-	for range t.N {
-		_ = FastIntLog2(uint(t.N/10 + 1))
+func BenchmarkFastLog2(b *testing.B) {
+	var i uint64 = 1
+	for b.Loop() {
+		_ = FastIntLog2(i/10 + 1)
+		i++
 	}
 }
 
-func BenchmarkStdMathLog2(t *testing.B) {
-	for range t.N {
-		_ = int(math.Log2(float64(t.N/10 + 1)))
+func BenchmarkStdMathLog2(b *testing.B) {
+	var i uint64 = 1
+	for b.Loop() {
+		_ = math.Log2(float64(i/10 + 1))
+		i++
 	}
 }

pkg/ecs/slice.go

@@ -60,7 +60,7 @@ func (a *Slice[T]) Set(index int, value T) *T {
 
 func (a *Slice[T]) Append(values ...T) []T {
 	a.data = append(a.data, values...)
-	disCap := 1 << (FastIntLog2(uint(len(a.data))) + 1)
+	disCap := 1 << (FastIntLog2(uint64(len(a.data))) + 1)
 	if cap(a.data) > disCap {
 		a.data = a.data[:len(a.data):disCap]
 	}