nip77: FetchIDsOnly()

nip77/negentropy/storage/accumulator.go

@@ -0,0 +1,49 @@
+package storage
+
+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])
+}