a flat bitset

server/ecs/bitset.go

@@ -0,0 +1,92 @@
+package ecs
+
+import (
+	"golang.org/x/exp/constraints"
+	"math/bits"
+	"unsafe"
+)
+
+const uintsize = uint(unsafe.Sizeof(BitSet{}.values[0]))
+
+type BitSet struct {
+	// TODO: this is not a BitSet, I'm just testing
+	values []uint
+}
+
+func (b *BitSet) Set(i Index) (old bool) {
+	index := uint(i) / uintsize
+	offset := uint(i) % uintsize
+	if index >= uint(len(b.values)) {
+		if index < uint(cap(b.values)) {
+			b.values = b.values[:index]
+		} else {
+			newValues := make([]uint, index+1)
+			copy(newValues, b.values)
+			b.values = newValues
+		}
+	}
+	v := &b.values[index]
+	mask := uint(1 << offset)
+	old = *v&mask != 0
+	*v |= mask
+	return
+}
+
+func (b *BitSet) Unset(i Index) (old bool) {
+	index := uint(i) / uintsize
+	offset := uint(i) % uintsize
+	if index < uint(len(b.values)) {
+		v := &b.values[index]
+		mask := uint(1 << offset)
+		old = *v&mask != 0
+		*v &= ^mask
+	}
+	return
+}
+
+func (b *BitSet) Contains(i Index) bool {
+	index := uint(i) / uintsize
+	offset := uint(i) % uintsize
+	return index < uint(len(b.values)) && b.values[index]&(1<<offset) != 0
+}
+
+func (b *BitSet) And(other *BitSet) *BitSet {
+	result := BitSet{values: make([]uint, min(len(b.values), len(other.values)))}
+	for i := range b.values {
+		result.values[i] = b.values[i] & other.values[i]
+	}
+	return &result
+}
+
+func (b *BitSet) AndNot(other BitSet) *BitSet {
+	result := BitSet{values: make([]uint, max(len(b.values), len(other.values)))}
+	for i := range b.values {
+		result.values[i] = b.values[i] & ^other.values[i]
+	}
+	return &result
+}
+
+func (b *BitSet) Range(f func(eid Index)) {
+	for i, v := range b.values {
+		base := int(unsafe.Sizeof(v)) * i
+		for v != 0 {
+			p := bits.TrailingZeros(v)
+			f(Index(base + p))
+			v ^= 1 << p
+		}
+	}
+}
+
+func max[T constraints.Integer](a, b T) T {
+	if a > b {
+		return a
+	}
+	return b
+}
+
+func min[T constraints.Integer](a, b T) T {
+	if a < b {
+		return a
+	}
+	return b
+}