From 29ce03be31ef216e3a93067acd31b3b40c79afce Mon Sep 17 00:00:00 2001
From: Tnze <cjd001113@outlook.com>
Date: Sat, 28 May 2022 01:39:33 +0800
Subject: [PATCH] a flat bitset

---
 server/ecs/bitest.go      | 58 ------------------------
 server/ecs/bitset.go      | 92 +++++++++++++++++++++++++++++++++++++++
 server/ecs/bitset_test.go | 28 ++++++++++++
 3 files changed, 120 insertions(+), 58 deletions(-)
 delete mode 100644 server/ecs/bitest.go
 create mode 100644 server/ecs/bitset.go
 create mode 100644 server/ecs/bitset_test.go

diff --git a/server/ecs/bitest.go b/server/ecs/bitest.go
deleted file mode 100644
index c33b9f5..0000000
--- a/server/ecs/bitest.go
+++ /dev/null
@@ -1,58 +0,0 @@
-package ecs
-
-type BitSetLike interface {
-	Set(i Index) (old bool)
-	Unset(i Index) (old bool)
-	Contains(i Index) bool
-	And(other BitSetLike) (result BitSetLike)
-	AndNot(other BitSetLike) (result BitSetLike)
-	Range(f func(eid Index))
-}
-
-type BitSet struct {
-	// TODO: this is not a BitSet, I'm just testing
-	values map[Index]struct{}
-}
-
-func (b BitSet) Set(i Index) (old bool) {
-	_, old = b.values[i]
-	b.values[i] = struct{}{}
-	return
-}
-
-func (b BitSet) Unset(i Index) (old bool) {
-	_, old = b.values[i]
-	delete(b.values, i)
-	return
-}
-
-func (b BitSet) Contains(i Index) bool {
-	_, contains := b.values[i]
-	return contains
-}
-
-func (b BitSet) And(other BitSetLike) BitSetLike {
-	result := BitSet{values: make(map[Index]struct{})}
-	for i := range b.values {
-		if other.Contains(i) {
-			result.values[i] = struct{}{}
-		}
-	}
-	return result
-}
-
-func (b BitSet) AndNot(other BitSetLike) BitSetLike {
-	result := BitSet{values: make(map[Index]struct{})}
-	for i := range b.values {
-		if !other.Contains(i) {
-			result.values[i] = struct{}{}
-		}
-	}
-	return result
-}
-
-func (b BitSet) Range(f func(eid Index)) {
-	for i := range b.values {
-		f(i)
-	}
-}
diff --git a/server/ecs/bitset.go b/server/ecs/bitset.go
new file mode 100644
index 0000000..28ab362
--- /dev/null
+++ b/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
+}
diff --git a/server/ecs/bitset_test.go b/server/ecs/bitset_test.go
new file mode 100644
index 0000000..ad82bbf
--- /dev/null
+++ b/server/ecs/bitset_test.go
@@ -0,0 +1,28 @@
+package ecs
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestBitSet_And(t *testing.T) {
+	var set1, set2 BitSet
+
+	set1.Set(1)
+	set1.Set(3)
+	set1.Set(40)
+
+	set2.Set(2)
+	set2.Set(3)
+	set2.Set(9)
+	set2.Set(40)
+
+	var results []Index
+	set1.And(&set2).Range(func(eid Index) {
+		results = append(results, eid)
+	})
+	want := []Index{3, 40}
+	if !reflect.DeepEqual(results, want) {
+		t.Errorf("want %v, got: %v", want, results)
+	}
+}