negentropy: fuzz testing, move accumulator to vector package.

nip77/negentropy/storage/vector/accumulator.go

@@ -0,0 +1,49 @@
+package vector
+
+import (
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+
+	"github.com/nbd-wtf/go-nostr/nip77/negentropy"
+)
+
+type Accumulator struct {
+	Buf [32 + 8]byte // leave 8 bytes at the end as a slack for use in GetFingerprint append()
+}
+
+func (acc *Accumulator) Reset() {
+	for i := 0; i < 32; i++ {
+		acc.Buf[i] = 0
+	}
+}
+
+func (acc *Accumulator) AddAccumulator(other Accumulator) {
+	acc.AddBytes(other.Buf[:32])
+}
+
+func (acc *Accumulator) AddBytes(other []byte) {
+	var currCarry, nextCarry uint32
+
+	for i := 0; i < 8; i++ {
+		offset := i * 4
+		orig := binary.LittleEndian.Uint32(acc.Buf[offset:])
+		otherV := binary.LittleEndian.Uint32(other[offset:])
+
+		next := orig + currCarry + otherV
+		if next < orig || next < otherV {
+			nextCarry = 1
+		}
+
+		binary.LittleEndian.PutUint32(acc.Buf[offset:32], next&0xFFFFFFFF)
+		currCarry = nextCarry
+		nextCarry = 0
+	}
+}
+
+func (acc *Accumulator) GetFingerprint(n int) string {
+	input := acc.Buf[:32]
+	input = append(input, negentropy.EncodeVarInt(n)...)
+	hash := sha256.Sum256(input)
+	return hex.EncodeToString(hash[:negentropy.FingerprintSize])
+}

nip77/negentropy/storage/vector/vector.go

@@ -13,6 +13,8 @@ import (
 type Vector struct {
 	items  []negentropy.Item
 	sealed bool
+
+	acc Accumulator
 }
 
 func New() *Vector {
@@ -21,14 +23,13 @@ func New() *Vector {
 	}
 }
 
-func (v *Vector) Insert(createdAt nostr.Timestamp, id string) error {
+func (v *Vector) Insert(createdAt nostr.Timestamp, id string) {
 	if len(id) != 64 {
-		return fmt.Errorf("bad id size for added item: expected %d bytes, got %d", 32, len(id)/2)
+		panic(fmt.Errorf("bad id size for added item: expected %d bytes, got %d", 32, len(id)/2))
 	}
 
 	item := negentropy.Item{Timestamp: createdAt, ID: id}
 	v.items = append(v.items, item)
-	return nil
 }
 
 func (v *Vector) Size() int { return len(v.items) }
@@ -63,15 +64,14 @@ func (v *Vector) FindLowerBound(begin, end int, bound negentropy.Bound) int {
 	return begin + idx
 }
 
-func (v *Vector) Fingerprint(begin, end int) [negentropy.FingerprintSize]byte {
-	var out negentropy.Accumulator
-	out.SetToZero()
+func (v *Vector) Fingerprint(begin, end int) string {
+	v.acc.Reset()
 
 	tmp := make([]byte, 32)
 	for _, item := range v.Range(begin, end) {
 		hex.Decode(tmp, []byte(item.ID))
-		out.AddBytes(tmp)
+		v.acc.AddBytes(tmp)
 	}
 
-	return out.GetFingerprint(end - begin)
+	return v.acc.GetFingerprint(end - begin)
 }