Merge pull request #90 from kcalvinalvin/2023-12-19-add-packed-hashes

chainhash: add packed hashes support

Author: kcalvinalvin

chaincfg/chainhash/hash.go

@@ -6,9 +6,11 @@
 package chainhash
 
 import (
+	"encoding/binary"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
+	"math"
 )
 
 // HashSize of array used to store hashes.  See Hash.
@@ -147,3 +149,69 @@ func Decode(dst *Hash, src string) error {
 
 	return nil
 }
+
+// Uint64sToPackedHashes packs the passed in uint64s into the 32 byte hashes. 4 uint64s are packed into
+// each 32 byte hash and if there's leftovers, it's filled with maxuint64.
+func Uint64sToPackedHashes(ints []uint64) []Hash {
+	// 4 uint64s fit into a 32 byte slice. For len(ints) < 4, count is 0.
+	count := len(ints) / 4
+
+	// If there's leftovers, we need to allocate 1 more.
+	if len(ints)%4 != 0 {
+		count++
+	}
+
+	hashes := make([]Hash, count)
+	hashIdx := 0
+	for i := range ints {
+		// Move on to the next hash after putting in 4 uint64s into a hash.
+		if i != 0 && i%4 == 0 {
+			hashIdx++
+		}
+
+		// 8 is the size of a uint64.
+		start := (i % 4) * 8
+		binary.LittleEndian.PutUint64(hashes[hashIdx][start:start+8], ints[i])
+	}
+
+	// Pad the last hash with math.MaxUint64 if needed. We check this by seeing
+	// if modulo 4 doesn't equate 0.
+	if len(ints)%4 != 0 {
+		// Start at the end.
+		end := HashSize
+
+		// Get the count of how many empty uint64 places we should pad.
+		padAmount := 4 - len(ints)%4
+		for i := 0; i < padAmount; i++ {
+			// 8 is the size of a uint64.
+			binary.LittleEndian.PutUint64(hashes[len(hashes)-1][end-8:end], math.MaxUint64)
+			end -= 8
+		}
+	}
+
+	return hashes
+}
+
+// PackedHashesToUint64 returns the uint64s in the packed hashes as a slice of uint64s.
+func PackedHashesToUint64(hashes []Hash) []uint64 {
+	ints := make([]uint64, 0, len(hashes)*4)
+	for i := range hashes {
+		// We pack 4 ints per hash.
+		for j := 0; j < 4; j++ {
+			// Offset for each int should be calculated by multiplying by
+			// the size of a uint64.
+			start := j * 8
+			read := binary.LittleEndian.Uint64(hashes[i][start : start+8])
+
+			// If we reach padded values, break.
+			if read == math.MaxUint64 {
+				break
+			}
+
+			// Otherwise we append the read uint64 to the slice.
+			ints = append(ints, read)
+		}
+	}
+
+	return ints
+}

chaincfg/chainhash/hash_test.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"encoding/hex"
 	"encoding/json"
+	"reflect"
 	"testing"
 )
 
@@ -220,3 +221,25 @@ func TestHashJsonMarshal(t *testing.T) {
 		t.Errorf("String: wrong hash string - got %v, want %v", newHash.String(), hashStr)
 	}
 }
+
+func TestPackedHashes(t *testing.T) {
+	tests := []struct {
+		uints []uint64
+	}{
+		{uints: []uint64{0, 1, 2, 3}},
+		{uints: []uint64{0, 1, 2, 3, 4}},
+		{uints: []uint64{0, 1, 2, 3, 4, 5}},
+		{uints: []uint64{0, 1, 2, 3, 4, 5, 6}},
+		{uints: []uint64{0, 1, 2, 3, 4, 5, 6, 7}},
+		{uints: []uint64{11, 22, 33, 44, 55}},
+	}
+
+	for _, test := range tests {
+		hashes := Uint64sToPackedHashes(test.uints)
+		got := PackedHashesToUint64(hashes)
+
+		if !reflect.DeepEqual(test.uints, got) {
+			t.Fatalf("expected %v but got %v", test.uints, got)
+		}
+	}
+}