Merge pull request #128 from hermeznetwork/feature/l1txbytes

Update common.L1Tx parsers, add test checks

common/account.go

@@ -37,7 +37,7 @@ type Idx uint32
 // Bytes returns a byte array representing the Idx
 func (idx Idx) Bytes() []byte {
 	var b [4]byte
-	binary.LittleEndian.PutUint32(b[:], uint32(idx))
+	binary.BigEndian.PutUint32(b[:], uint32(idx))
 	return b[:]
 }
 
@@ -51,7 +51,7 @@ func IdxFromBytes(b []byte) (Idx, error) {
 	if len(b) != idxBytesLen {
 		return 0, fmt.Errorf("can not parse Idx, bytes len %d, expected 4", len(b))
 	}
-	idx := binary.LittleEndian.Uint32(b[:4])
+	idx := binary.BigEndian.Uint32(b[:4])
 	return Idx(idx), nil
 }
 
@@ -84,7 +84,10 @@ func (a *Account) String() string {
 	return buf.String()
 }
 
-// Bytes returns the bytes representing the Account, in a way that each BigInt is represented by 32 bytes, in spite of the BigInt could be represented in less bytes (due a small big.Int), so in this way each BigInt is always 32 bytes and can be automatically parsed from a byte array.
+// Bytes returns the bytes representing the Account, in a way that each BigInt
+// is represented by 32 bytes, in spite of the BigInt could be represented in
+// less bytes (due a small big.Int), so in this way each BigInt is always 32
+// bytes and can be automatically parsed from a byte array.
 func (a *Account) Bytes() ([32 * NLeafElems]byte, error) {
 	var b [32 * NLeafElems]byte
 
@@ -105,7 +108,7 @@ func (a *Account) Bytes() ([32 * NLeafElems]byte, error) {
 	if babyjub.PointCoordSign(a.PublicKey.X) {
 		b[10] = 1
 	}
-	copy(b[32:64], SwapEndianness(a.Balance.Bytes())) // SwapEndianness, as big.Int uses BigEndian
+	copy(b[32:64], SwapEndianness(a.Balance.Bytes()))
 	copy(b[64:96], SwapEndianness(a.PublicKey.Y.Bytes()))
 	copy(b[96:116], a.EthAddr.Bytes())
 
@@ -159,7 +162,10 @@ func AccountFromBigInts(e [NLeafElems]*big.Int) (*Account, error) {
 
 // AccountFromBytes returns a Account from a byte array
 func AccountFromBytes(b [32 * NLeafElems]byte) (*Account, error) {
-	tokenID := binary.LittleEndian.Uint32(b[0:4])
+	tokenID, err := TokenIDFromBytes(b[0:4])
+	if err != nil {
+		return nil, err
+	}
 	var nonceBytes5 [5]byte
 	copy(nonceBytes5[:], b[4:9])
 	nonce := NonceFromBytes(nonceBytes5)

common/account_test.go

@@ -106,7 +106,7 @@ func TestAccountHashValue(t *testing.T) {
 
 	v, err := account.HashValue()
 	assert.Nil(t, err)
-	assert.Equal(t, "16085711911723375585301279875451049849443101031421093098714359651259271023730", v.String())
+	assert.Equal(t, "9478468711598093334066833736294178928569163287501434518121324135729106649559", v.String())
 }
 
 func TestAccountErrNotInFF(t *testing.T) {

common/float16.go

@@ -0,0 +1,129 @@
+// Package common Float16 provides methods to work with Hermez custom half float
+// precision, 16 bits, codification internally called Float16 has been adopted
+// to encode large integers. This is done in order to save bits when L2
+// transactions are published.
+//nolint:gomnd
+package common
+
+import (
+	"encoding/binary"
+	"errors"
+	"math/big"
+)
+
+var (
+	// ErrRoundingLoss is used when converted big.Int to Float16 causes rounding loss
+	ErrRoundingLoss = errors.New("input value causes rounding loss")
+)
+
+// Float16 represents a float in a 16 bit format
+type Float16 uint16
+
+// Bytes return a byte array of length 2 with the Float16 value encoded in BigEndian
+func (f16 Float16) Bytes() []byte {
+	var b [2]byte
+	binary.BigEndian.PutUint16(b[:], uint16(f16))
+	return b[:]
+}
+
+// Float16FromBytes returns a Float16 from a byte array of 2 bytes.
+func Float16FromBytes(b []byte) *Float16 {
+	f16 := Float16(binary.BigEndian.Uint16(b[:2]))
+	return &f16
+}
+
+// BigInt converts the Float16 to a *big.Int integer
+func (f16 *Float16) BigInt() *big.Int {
+	fl := int64(*f16)
+
+	m := big.NewInt(fl & 0x3FF)
+	e := big.NewInt(fl >> 11)
+	e5 := (fl >> 10) & 0x01
+
+	exp := big.NewInt(0).Exp(big.NewInt(10), e, nil)
+	res := m.Mul(m, exp)
+
+	if e5 != 0 && e.Cmp(big.NewInt(0)) != 0 {
+		res.Add(res, exp.Div(exp, big.NewInt(2)))
+	}
+	return res
+}
+
+// floorFix2Float converts a fix to a float, always rounding down
+func floorFix2Float(_f *big.Int) Float16 {
+	zero := big.NewInt(0)
+	ten := big.NewInt(10)
+	e := int64(0)
+
+	m := big.NewInt(0)
+	m.Set(_f)
+
+	if m.Cmp(zero) == 0 {
+		return 0
+	}
+
+	s := big.NewInt(0).Rsh(m, 10)
+
+	for s.Cmp(zero) != 0 {
+		m.Div(m, ten)
+		s.Rsh(m, 10)
+		e++
+	}
+
+	return Float16(m.Int64() | e<<11)
+}
+
+// NewFloat16 encodes a *big.Int integer as a Float16, returning error in
+// case of loss during the encoding.
+func NewFloat16(f *big.Int) (Float16, error) {
+	fl1 := floorFix2Float(f)
+	fi1 := fl1.BigInt()
+	fl2 := fl1 | 0x400
+	fi2 := fl2.BigInt()
+
+	m3 := (fl1 & 0x3FF) + 1
+	e3 := fl1 >> 11
+
+	if m3&0x400 == 0 {
+		m3 = 0x66
+		e3++
+	}
+
+	fl3 := m3 + e3<<11
+	fi3 := fl3.BigInt()
+
+	res := fl1
+
+	d := big.NewInt(0).Abs(fi1.Sub(fi1, f))
+	d2 := big.NewInt(0).Abs(fi2.Sub(fi2, f))
+
+	if d.Cmp(d2) == 1 {
+		res = fl2
+		d = d2
+	}
+
+	d3 := big.NewInt(0).Abs(fi3.Sub(fi3, f))
+
+	if d.Cmp(d3) == 1 {
+		res = fl3
+	}
+
+	// Do rounding check
+	if res.BigInt().Cmp(f) == 0 {
+		return res, nil
+	}
+	return res, ErrRoundingLoss
+}
+
+// NewFloat16Floor encodes a big.Int integer as a Float16, rounding down in
+// case of loss during the encoding.
+func NewFloat16Floor(f *big.Int) Float16 {
+	fl1 := floorFix2Float(f)
+	fl2 := fl1 | 0x400
+	fi2 := fl2.BigInt()
+
+	if fi2.Cmp(f) < 1 {
+		return fl2
+	}
+	return fl1
+}

common/float16_test.go

@@ -0,0 +1,131 @@
+package common
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestConversions(t *testing.T) {
+	testVector := map[Float16]string{
+		0x307B: "123000000",
+		0x1DC6: "454500",
+		0xFFFF: "10235000000000000000000000000000000",
+		0x0000: "0",
+		0x0400: "0",
+		0x0001: "1",
+		0x0401: "1",
+		0x0800: "0",
+		0x0c00: "5",
+		0x0801: "10",
+		0x0c01: "15",
+	}
+
+	for test := range testVector {
+		fix := test.BigInt()
+
+		assert.Equal(t, fix.String(), testVector[test])
+
+		bi := big.NewInt(0)
+		bi.SetString(testVector[test], 10)
+
+		fl, err := NewFloat16(bi)
+		assert.Equal(t, nil, err)
+
+		fx2 := fl.BigInt()
+		assert.Equal(t, fx2.String(), testVector[test])
+	}
+}
+
+func TestFloorFix2Float(t *testing.T) {
+	testVector := map[string]Float16{
+		"87999990000000000": 0x776f,
+		"87950000000000001": 0x776f,
+		"87950000000000000": 0x776f,
+		"87949999999999999": 0x736f,
+	}
+
+	for test := range testVector {
+		bi := big.NewInt(0)
+		bi.SetString(test, 10)
+
+		testFloat := NewFloat16Floor(bi)
+
+		assert.Equal(t, testFloat, testVector[test])
+	}
+}
+
+func TestConversionLosses(t *testing.T) {
+	a := big.NewInt(1000)
+	b, err := NewFloat16(a)
+	assert.Equal(t, nil, err)
+	c := b.BigInt()
+	assert.Equal(t, c, a)
+
+	a = big.NewInt(1024)
+	b, err = NewFloat16(a)
+	assert.Equal(t, ErrRoundingLoss, err)
+	c = b.BigInt()
+	assert.NotEqual(t, c, a)
+
+	a = big.NewInt(32767)
+	b, err = NewFloat16(a)
+	assert.Equal(t, ErrRoundingLoss, err)
+	c = b.BigInt()
+	assert.NotEqual(t, c, a)
+
+	a = big.NewInt(32768)
+	b, err = NewFloat16(a)
+	assert.Equal(t, ErrRoundingLoss, err)
+	c = b.BigInt()
+	assert.NotEqual(t, c, a)
+
+	a = big.NewInt(65536000)
+	b, err = NewFloat16(a)
+	assert.Equal(t, ErrRoundingLoss, err)
+	c = b.BigInt()
+	assert.NotEqual(t, c, a)
+}
+
+func BenchmarkFloat16(b *testing.B) {
+	newBigInt := func(s string) *big.Int {
+		bigInt, ok := new(big.Int).SetString(s, 10)
+		if !ok {
+			panic("Bad big int")
+		}
+		return bigInt
+	}
+	type pair struct {
+		Float16 Float16
+		BigInt  *big.Int
+	}
+	testVector := []pair{
+		{0x307B, newBigInt("123000000")},
+		{0x1DC6, newBigInt("454500")},
+		{0xFFFF, newBigInt("10235000000000000000000000000000000")},
+		{0x0000, newBigInt("0")},
+		{0x0400, newBigInt("0")},
+		{0x0001, newBigInt("1")},
+		{0x0401, newBigInt("1")},
+		{0x0800, newBigInt("0")},
+		{0x0c00, newBigInt("5")},
+		{0x0801, newBigInt("10")},
+		{0x0c01, newBigInt("15")},
+	}
+	b.Run("floorFix2Float()", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			NewFloat16Floor(testVector[i%len(testVector)].BigInt)
+		}
+	})
+	b.Run("NewFloat16()", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			_, _ = NewFloat16(testVector[i%len(testVector)].BigInt)
+		}
+	})
+	b.Run("Float16.BigInt()", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			testVector[i%len(testVector)].Float16.BigInt()
+		}
+	})
+}

common/l1tx.go

@@ -1,6 +1,7 @@
 package common
 
 import (
+	"fmt"
 	"math/big"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
@@ -8,11 +9,8 @@ import (
 )
 
 const (
-	fromBJJCompressedB = 256
-	fromEthAddrB       = 160
-	f16B               = 16
-	tokenIDB           = 32
-	cidXB              = 32
+	// L1TxBytesLen is the length of the byte array that represents the L1Tx
+	L1TxBytesLen = 68
 )
 
 // L1Tx is a struct that represents a L1 tx
@@ -64,69 +62,57 @@ func (tx *L1Tx) Tx() *Tx {
 }
 
 // Bytes encodes a L1Tx into []byte
-func (tx *L1Tx) Bytes(nLevels int) []byte {
-	res := big.NewInt(0)
-	res = res.Add(res, big.NewInt(0).Or(big.NewInt(0), tx.ToIdx.BigInt()))
-	res = res.Add(res, big.NewInt(0).Lsh(big.NewInt(0).Or(big.NewInt(0), big.NewInt(int64(tx.TokenID))), uint(nLevels)))
-	res = res.Add(res, big.NewInt(0).Lsh(big.NewInt(0).Or(big.NewInt(0), tx.Amount), uint(nLevels+tokenIDB)))
-	res = res.Add(res, big.NewInt(0).Lsh(big.NewInt(0).Or(big.NewInt(0), tx.LoadAmount), uint(nLevels+tokenIDB+f16B)))
-	res = res.Add(res, big.NewInt(0).Lsh(big.NewInt(0).Or(big.NewInt(0), tx.FromIdx.BigInt()), uint(nLevels+tokenIDB+2*f16B)))
-
-	fromBJJ := big.NewInt(0)
-	fromBJJ.SetString(tx.FromBJJ.String(), 16)
-	fromBJJCompressed := big.NewInt(0).Or(big.NewInt(0), fromBJJ)
-	res = res.Add(res, big.NewInt(0).Lsh(fromBJJCompressed, uint(2*nLevels+tokenIDB+2*f16B)))
-
-	fromEthAddr := big.NewInt(0).Or(big.NewInt(0), tx.FromEthAddr.Hash().Big())
-	res = res.Add(res, big.NewInt(0).Lsh(fromEthAddr, uint(fromBJJCompressedB+2*nLevels+tokenIDB+2*f16B)))
-
-	return res.Bytes()
+func (tx *L1Tx) Bytes(nLevels int) ([]byte, error) {
+	var b [68]byte
+	copy(b[0:20], tx.FromEthAddr.Bytes())
+	pkComp := tx.FromBJJ.Compress()
+	copy(b[20:52], pkComp[:])
+	copy(b[52:56], tx.FromIdx.Bytes())
+	loadAmountFloat16, err := NewFloat16(tx.LoadAmount)
+	if err != nil {
+		return nil, err
+	}
+	copy(b[56:58], loadAmountFloat16.Bytes())
+	amountFloat16, err := NewFloat16(tx.Amount)
+	if err != nil {
+		return nil, err
+	}
+	copy(b[58:60], amountFloat16.Bytes())
+	copy(b[60:64], tx.TokenID.Bytes())
+	copy(b[64:68], tx.ToIdx.Bytes())
+	return b[:], nil
 }
 
 // L1TxFromBytes decodes a L1Tx from []byte
-func L1TxFromBytes(l1TxEncoded []byte) (*L1Tx, error) {
-	l1Tx := &L1Tx{}
-	var idxB uint = cidXB
-
-	l1TxEncodedBI := big.NewInt(0)
-	l1TxEncodedBI.SetBytes(l1TxEncoded)
-
-	toIdx, err := IdxFromBigInt(extract(l1TxEncodedBI, 0, idxB))
-
-	if err != nil {
-		return nil, err
+func L1TxFromBytes(b []byte) (*L1Tx, error) {
+	if len(b) != L1TxBytesLen {
+		return nil, fmt.Errorf("Can not parse L1Tx bytes, expected length %d, current: %d", 68, len(b))
 	}
 
-	l1Tx.ToIdx = toIdx
-
-	l1Tx.TokenID = TokenID(extract(l1TxEncodedBI, idxB, tokenIDB).Uint64())
-	l1Tx.Amount = extract(l1TxEncodedBI, idxB+tokenIDB, f16B)
-	l1Tx.LoadAmount = extract(l1TxEncodedBI, idxB+tokenIDB+f16B, f16B)
-	fromIdx, err := IdxFromBigInt(extract(l1TxEncodedBI, idxB+tokenIDB+2*f16B, f16B))
-
-	if err != nil {
-		return nil, err
-	}
-
-	l1Tx.FromIdx = fromIdx
-
+	tx := &L1Tx{}
+	var err error
+	tx.FromEthAddr = ethCommon.BytesToAddress(b[0:20])
+	pkCompB := b[20:52]
 	var pkComp babyjub.PublicKeyComp
-	copy(pkComp[:], extract(l1TxEncodedBI, 2*idxB+tokenIDB+2*f16B, fromBJJCompressedB).Bytes())
-	pk, err := pkComp.Decompress()
-
+	copy(pkComp[:], pkCompB)
+	tx.FromBJJ, err = pkComp.Decompress()
+	if err != nil {
+		return nil, err
+	}
+	tx.FromIdx, err = IdxFromBytes(b[52:56])
+	if err != nil {
+		return nil, err
+	}
+	tx.LoadAmount = Float16FromBytes(b[56:58]).BigInt()
+	tx.Amount = Float16FromBytes(b[58:60]).BigInt()
+	tx.TokenID, err = TokenIDFromBytes(b[60:64])
+	if err != nil {
+		return nil, err
+	}
+	tx.ToIdx, err = IdxFromBytes(b[64:68])
 	if err != nil {
 		return nil, err
 	}
 
-	l1Tx.FromBJJ = pk
-
-	l1Tx.FromEthAddr = ethCommon.BigToAddress(extract(l1TxEncodedBI, fromBJJCompressedB+2*idxB+tokenIDB+2*f16B, fromEthAddrB))
-
-	return l1Tx, nil
-}
-
-// extract masks and shifts a bigInt
-func extract(num *big.Int, origin uint, len uint) *big.Int {
-	mask := big.NewInt(0).Sub(big.NewInt(0).Lsh(big.NewInt(1), len), big.NewInt(1))
-	return big.NewInt(0).And(big.NewInt(0).Rsh(num, origin), mask)
+	return tx, nil
 }

common/l1tx_test.go

@@ -11,7 +11,7 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-func TestL1TxCodec(t *testing.T) {
+func TestL1TxByteParsers(t *testing.T) {
 	var pkComp babyjub.PublicKeyComp
 	err := pkComp.UnmarshalText([]byte("0x56ca90f80d7c374ae7485e9bcc47d4ac399460948da6aeeb899311097925a72c"))
 	require.Nil(t, err)
@@ -19,7 +19,7 @@ func TestL1TxCodec(t *testing.T) {
 	pk, err := pkComp.Decompress()
 	require.Nil(t, err)
 
-	l1Tx := L1Tx{
+	l1Tx := &L1Tx{
 		ToIdx:       3,
 		TokenID:     5,
 		Amount:      big.NewInt(1),
@@ -32,12 +32,23 @@ func TestL1TxCodec(t *testing.T) {
 	expected, err := utils.HexDecode("c58d29fa6e86e4fae04ddced660d45bcf3cb237056ca90f80d7c374ae7485e9bcc47d4ac399460948da6aeeb899311097925a72c00000002000200010000000500000003")
 	require.Nil(t, err)
 
-	encodedData := l1Tx.Bytes(32)
+	encodedData, err := l1Tx.Bytes(32)
+	require.Nil(t, err)
 	assert.Equal(t, expected, encodedData)
 
 	decodedData, err := L1TxFromBytes(encodedData)
 	require.Nil(t, err)
+	assert.Equal(t, l1Tx, decodedData)
 
-	encodedData2 := decodedData.Bytes(32)
+	encodedData2, err := decodedData.Bytes(32)
+	require.Nil(t, err)
 	assert.Equal(t, encodedData, encodedData2)
+
+	// expect error if length!=68
+	_, err = L1TxFromBytes(encodedData[:66])
+	require.NotNil(t, err)
+	_, err = L1TxFromBytes([]byte{})
+	require.NotNil(t, err)
+	_, err = L1TxFromBytes(nil)
+	require.NotNil(t, err)
 }

common/pooll2tx.go

@@ -7,7 +7,6 @@ import (
 	"time"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
-	"github.com/hermeznetwork/hermez-node/utils"
 	"github.com/iden3/go-iden3-crypto/babyjub"
 	"github.com/iden3/go-iden3-crypto/poseidon"
 )
@@ -21,9 +20,9 @@ func (n Nonce) Bytes() ([5]byte, error) {
 		return [5]byte{}, ErrNonceOverflow
 	}
 	var nonceBytes [8]byte
-	binary.LittleEndian.PutUint64(nonceBytes[:], uint64(n))
+	binary.BigEndian.PutUint64(nonceBytes[:], uint64(n))
 	var b [5]byte
-	copy(b[:], nonceBytes[:5])
+	copy(b[:], nonceBytes[3:])
 	return b, nil
 }
 
@@ -35,8 +34,8 @@ func (n Nonce) BigInt() *big.Int {
 // NonceFromBytes returns Nonce from a [5]byte
 func NonceFromBytes(b [5]byte) Nonce {
 	var nonceBytes [8]byte
-	copy(nonceBytes[:], b[:5])
-	nonce := binary.LittleEndian.Uint64(nonceBytes[:])
+	copy(nonceBytes[3:], b[:])
+	nonce := binary.BigEndian.Uint64(nonceBytes[:])
 	return Nonce(nonce)
 }
 
@@ -75,15 +74,15 @@ type PoolL2Tx struct {
 }
 
 // TxCompressedData spec:
-// [ 32 bits ] signatureConstant // 4 bytes: [0:4]
-// [ 16 bits ] chainId // 2 bytes: [4:6]
-// [ 48 bits ] fromIdx // 6 bytes: [6:12]
-// [ 48 bits ] toIdx // 6 bytes: [12:18]
-// [ 16 bits ] amountFloat16 // 2 bytes: [18:20]
-// [ 32 bits ] tokenID // 4 bytes: [20:24]
-// [ 40 bits ] nonce // 5 bytes: [24:29]
-// [ 8 bits  ] userFee // 1 byte: [29:30]
-// [ 1 bits  ] toBJJSign // 1 byte: [30:31]
+// [ 1 bits  ] toBJJSign // 1 byte
+// [ 8 bits  ] userFee // 1 byte
+// [ 40 bits ] nonce // 5 bytes
+// [ 32 bits ] tokenID // 4 bytes
+// [ 16 bits ] amountFloat16 // 2 bytes
+// [ 48 bits ] toIdx // 6 bytes
+// [ 48 bits ] fromIdx // 6 bytes
+// [ 16 bits ] chainId // 2 bytes
+// [ 32 bits ] signatureConstant // 4 bytes
 // Total bits compressed data:  241 bits // 31 bytes in *big.Int representation
 func (tx *PoolL2Tx) TxCompressedData() (*big.Int, error) {
 	// sigconstant
@@ -92,65 +91,65 @@ func (tx *PoolL2Tx) TxCompressedData() (*big.Int, error) {
 		return nil, fmt.Errorf("error parsing SignatureConstant")
 	}
 
-	amountFloat16, err := utils.NewFloat16(tx.Amount)
+	amountFloat16, err := NewFloat16(tx.Amount)
 	if err != nil {
 		return nil, err
 	}
 	var b [31]byte
-	copy(b[:4], SwapEndianness(sc.Bytes()))
-	copy(b[4:6], []byte{1, 0, 0, 0}) // LittleEndian representation of uint32(1) for Ethereum
-	copy(b[6:12], tx.FromIdx.Bytes())
-	copy(b[12:18], tx.ToIdx.Bytes())
-	copy(b[18:20], amountFloat16.Bytes())
-	copy(b[20:24], tx.TokenID.Bytes())
-	nonceBytes, err := tx.Nonce.Bytes()
-	if err != nil {
-		return nil, err
-	}
-	copy(b[24:29], nonceBytes[:])
-	b[29] = byte(tx.Fee)
 	toBJJSign := byte(0)
 	if babyjub.PointCoordSign(tx.ToBJJ.X) {
 		toBJJSign = byte(1)
 	}
-	b[30] = toBJJSign
-	bi := new(big.Int).SetBytes(SwapEndianness(b[:]))
+	b[0] = toBJJSign
+	b[1] = byte(tx.Fee)
+	nonceBytes, err := tx.Nonce.Bytes()
+	if err != nil {
+		return nil, err
+	}
+	copy(b[2:7], nonceBytes[:])
+	copy(b[7:11], tx.TokenID.Bytes())
+	copy(b[11:13], amountFloat16.Bytes())
+	copy(b[13+2:19], tx.ToIdx.Bytes())
+	copy(b[19+2:25], tx.FromIdx.Bytes())
+	copy(b[25:27], []byte{0, 1, 0, 0}) // TODO check js implementation (unexpected behaviour from test vector generated from js)
+	copy(b[27:31], sc.Bytes())
 
+	bi := new(big.Int).SetBytes(b[:])
 	return bi, nil
 }
 
 // TxCompressedDataV2 spec:
-// [ 48 bits ] fromIdx // 6 bytes: [0:6]
-// [ 48 bits ] toIdx // 6 bytes: [6:12]
-// [ 16 bits ] amountFloat16 // 2 bytes: [12:14]
-// [ 32 bits ] tokenID // 4 bytes: [14:18]
-// [ 40 bits ] nonce // 5 bytes: [18:23]
-// [ 8 bits  ] userFee // 1 byte: [23:24]
-// [ 1 bits  ] toBJJSign // 1 byte: [24:25]
+// [ 1 bits  ] toBJJSign // 1 byte
+// [ 8 bits  ] userFee // 1 byte
+// [ 40 bits ] nonce // 5 bytes
+// [ 32 bits ] tokenID // 4 bytes
+// [ 16 bits ] amountFloat16 // 2 bytes
+// [ 48 bits ] toIdx // 6 bytes
+// [ 48 bits ] fromIdx // 6 bytes
 // Total bits compressed data:  193 bits // 25 bytes in *big.Int representation
 func (tx *PoolL2Tx) TxCompressedDataV2() (*big.Int, error) {
-	amountFloat16, err := utils.NewFloat16(tx.Amount)
+	amountFloat16, err := NewFloat16(tx.Amount)
 	if err != nil {
 		return nil, err
 	}
 	var b [25]byte
-	copy(b[0:6], tx.FromIdx.Bytes())
-	copy(b[6:12], tx.ToIdx.Bytes())
-	copy(b[12:14], amountFloat16.Bytes())
-	copy(b[14:18], tx.TokenID.Bytes())
-	nonceBytes, err := tx.Nonce.Bytes()
-	if err != nil {
-		return nil, err
-	}
-	copy(b[18:23], nonceBytes[:])
-	b[23] = byte(tx.Fee)
 	toBJJSign := byte(0)
 	if babyjub.PointCoordSign(tx.ToBJJ.X) {
 		toBJJSign = byte(1)
 	}
-	b[24] = toBJJSign
+	b[0] = toBJJSign
+	b[1] = byte(tx.Fee)
+	nonceBytes, err := tx.Nonce.Bytes()
+	if err != nil {
+		return nil, err
+	}
+	copy(b[2:7], nonceBytes[:])
+	copy(b[7:11], tx.TokenID.Bytes())
+	copy(b[11:13], amountFloat16.Bytes())
+	copy(b[13+2:19], tx.ToIdx.Bytes())
+	copy(b[19+2:25], tx.FromIdx.Bytes())
 
-	bi := new(big.Int).SetBytes(SwapEndianness(b[:]))
+	bi := new(big.Int).SetBytes(b[:])
 	return bi, nil
 }
 

common/pooll2tx_test.go

@@ -15,7 +15,7 @@ func TestNonceParser(t *testing.T) {
 	nBytes, err := n.Bytes()
 	assert.Nil(t, err)
 	assert.Equal(t, 5, len(nBytes))
-	assert.Equal(t, "0100000000", hex.EncodeToString(nBytes[:]))
+	assert.Equal(t, "0000000001", hex.EncodeToString(nBytes[:]))
 	n2 := NonceFromBytes(nBytes)
 	assert.Equal(t, n, n2)
 
@@ -51,7 +51,11 @@ func TestTxCompressedData(t *testing.T) {
 	txCompressedData, err := tx.TxCompressedData()
 	assert.Nil(t, err)
 	// test vector value generated from javascript implementation
-	assert.Equal(t, "1766847064778421992193717128424891165872736891548909569553540449389241871", txCompressedData.String())
+	expectedStr := "1766847064778421992193717128424891165872736891548909569553540449389241871"
+	assert.Equal(t, expectedStr, txCompressedData.String())
+	expected, ok := new(big.Int).SetString(expectedStr, 10)
+	assert.True(t, ok)
+	assert.Equal(t, expected.Bytes(), txCompressedData.Bytes())
 	assert.Equal(t, "10000000000060000000500040000000000030000000000020001c60be60f", hex.EncodeToString(txCompressedData.Bytes())[1:])
 
 	tx = PoolL2Tx{
@@ -66,7 +70,11 @@ func TestTxCompressedData(t *testing.T) {
 	txCompressedData, err = tx.TxCompressedDataV2()
 	assert.Nil(t, err)
 	// test vector value generated from javascript implementation
-	assert.Equal(t, "6571340879233176732837827812956721483162819083004853354503", txCompressedData.String())
+	expectedStr = "6571340879233176732837827812956721483162819083004853354503"
+	assert.Equal(t, expectedStr, txCompressedData.String())
+	expected, ok = new(big.Int).SetString(expectedStr, 10)
+	assert.True(t, ok)
+	assert.Equal(t, expected.Bytes(), txCompressedData.Bytes())
 	assert.Equal(t, "10c000000000b0000000a0009000000000008000000000007", hex.EncodeToString(txCompressedData.Bytes())[1:])
 }
 

common/token.go

@@ -2,12 +2,16 @@ package common
 
 import (
 	"encoding/binary"
+	"fmt"
 	"math/big"
 	"time"
 
 	ethCommon "github.com/ethereum/go-ethereum/common"
 )
 
+// tokenIDBytesLen defines the length of the TokenID byte array representation
+const tokenIDBytesLen = 4
+
 // Token is a struct that represents an Ethereum token that is supported in Hermez network
 type Token struct {
 	TokenID     TokenID           `meddler:"token_id"`
@@ -33,7 +37,7 @@ type TokenID uint32 // current implementation supports up to 2^32 tokens
 // Bytes returns a byte array of length 4 representing the TokenID
 func (t TokenID) Bytes() []byte {
 	var tokenIDBytes [4]byte
-	binary.LittleEndian.PutUint32(tokenIDBytes[:], uint32(t))
+	binary.BigEndian.PutUint32(tokenIDBytes[:], uint32(t))
 	return tokenIDBytes[:]
 }
 
@@ -41,3 +45,12 @@ func (t TokenID) Bytes() []byte {
 func (t TokenID) BigInt() *big.Int {
 	return big.NewInt(int64(t))
 }
+
+// TokenIDFromBytes returns TokenID from a byte array
+func TokenIDFromBytes(b []byte) (TokenID, error) {
+	if len(b) != tokenIDBytesLen {
+		return 0, fmt.Errorf("can not parse TokenID, bytes len %d, expected 4", len(b))
+	}
+	tid := binary.BigEndian.Uint32(b[:4])
+	return TokenID(tid), nil
+}