fixedn: allow to parse big decimals

cli/wallet/nep17.go

@@ -391,14 +391,14 @@ func multiTransferNEP17(ctx *cli.Context) error {
 		if err != nil {
 			return cli.NewExitError(fmt.Errorf("invalid address: '%s'", ss[1]), 1)
 		}
-		amount, err := fixedn.FixedNFromString(ss[2], int(token.Decimals))
+		amount, err := fixedn.FromString(ss[2], int(token.Decimals))
 		if err != nil {
 			return cli.NewExitError(fmt.Errorf("invalid amount: %w", err), 1)
 		}
 		recipients = append(recipients, client.TransferTarget{
 			Token:   token.Hash,
 			Address: addr,
-			Amount:  amount,
+			Amount:  amount.Int64(),
 		})
 	}
 
@@ -438,7 +438,7 @@ func transferNEP17(ctx *cli.Context) error {
 		}
 	}
 
-	amount, err := fixedn.FixedNFromString(ctx.String("amount"), int(token.Decimals))
+	amount, err := fixedn.FromString(ctx.String("amount"), int(token.Decimals))
 	if err != nil {
 		return cli.NewExitError(fmt.Errorf("invalid amount: %w", err), 1)
 	}
@@ -446,7 +446,7 @@ func transferNEP17(ctx *cli.Context) error {
 	return signAndSendTransfer(ctx, c, acc, []client.TransferTarget{{
 		Token:   token.Hash,
 		Address: to,
-		Amount:  amount,
+		Amount:  amount.Int64(),
 	}})
 }
 

pkg/encoding/fixedn/decimal.go

@@ -0,0 +1,80 @@
+package fixedn
+
+import (
+	"errors"
+	"fmt"
+	"math/big"
+	"strconv"
+	"strings"
+)
+
+const maxAllowedPrecision = 16
+
+// ErrInvalidFormat is returned when decimal format is invalid.
+var ErrInvalidFormat = errors.New("invalid decimal format")
+
+var _pow10 []*big.Int
+
+func init() {
+	var p = int64(1)
+	for i := 0; i <= maxAllowedPrecision; i++ {
+		_pow10 = append(_pow10, big.NewInt(p))
+		p *= 10
+	}
+}
+
+func pow10(n int) *big.Int {
+	last := len(_pow10) - 1
+	if n <= last {
+		return _pow10[n]
+	}
+	p := new(big.Int)
+	p.Mul(_pow10[last], _pow10[1])
+	for i := last + 1; i < n; i++ {
+		p.Mul(p, _pow10[1])
+	}
+	return p
+}
+
+// ToString converts big decimal with specified precision to string.
+func ToString(bi *big.Int, precision int) string {
+	var dp, fp big.Int
+	dp.QuoRem(bi, pow10(precision), &fp)
+
+	var s = dp.String()
+	if fp.Sign() == 0 {
+		return s
+	}
+	frac := fp.Uint64()
+	trimmed := 0
+	for ; frac%10 == 0; frac /= 10 {
+		trimmed++
+	}
+	return s + "." + fmt.Sprintf("%0"+strconv.FormatUint(uint64(precision-trimmed), 10)+"d", frac)
+}
+
+// FromString converts string to a big decimal with specified precision.
+func FromString(s string, precision int) (*big.Int, error) {
+	parts := strings.SplitN(s, ".", 2)
+	bi, ok := new(big.Int).SetString(parts[0], 10)
+	if !ok {
+		return nil, ErrInvalidFormat
+	}
+	bi.Mul(bi, pow10(precision))
+	if len(parts) == 1 {
+		return bi, nil
+	}
+
+	if len(parts[1]) > precision {
+		return nil, ErrInvalidFormat
+	}
+	fp, ok := new(big.Int).SetString(parts[1], 10)
+	if !ok {
+		return nil, ErrInvalidFormat
+	}
+	fp.Mul(fp, pow10(precision-len(parts[1])))
+	if bi.Sign() == -1 {
+		return bi.Sub(bi, fp), nil
+	}
+	return bi.Add(bi, fp), nil
+}

pkg/encoding/fixedn/decimal_test.go

@@ -0,0 +1,51 @@
+package fixedn
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDecimalFromStringGood(t *testing.T) {
+	var testCases = []struct {
+		bi   *big.Int
+		prec int
+		s    string
+	}{
+		{big.NewInt(123), 2, "1.23"},
+		{big.NewInt(12300), 2, "123"},
+		{big.NewInt(1234500000), 8, "12.345"},
+		{big.NewInt(-12345), 3, "-12.345"},
+		{big.NewInt(35), 8, "0.00000035"},
+		{big.NewInt(1230), 5, "0.0123"},
+		{big.NewInt(123456789), 20, "0.00000000000123456789"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.s, func(t *testing.T) {
+			s := ToString(tc.bi, tc.prec)
+			require.Equal(t, tc.s, s)
+
+			bi, err := FromString(s, tc.prec)
+			require.NoError(t, err)
+			require.Equal(t, tc.bi, bi)
+		})
+	}
+}
+
+func TestDecimalFromStringBad(t *testing.T) {
+	var errCases = []struct {
+		s    string
+		prec int
+	}{
+		{"12A", 1},
+		{"12.345", 2},
+		{"12.3A", 2},
+	}
+	for _, tc := range errCases {
+		t.Run(tc.s, func(t *testing.T) {
+			_, err := FromString(tc.s, tc.prec)
+			require.Error(t, err)
+		})
+	}
+}

pkg/encoding/fixedn/fixed8.go

@@ -3,7 +3,6 @@ package fixedn
 import (
 	"encoding/json"
 	"errors"
-	"math"
 	"strconv"
 	"strings"
 
@@ -72,36 +71,11 @@ func Fixed8FromFloat(val float64) Fixed8 {
 // Fixed8FromString parses s which must be a fixed point number
 // with precision up to 10^-8
 func Fixed8FromString(s string) (Fixed8, error) {
-	num, err := FixedNFromString(s, precision)
+	num, err := FromString(s, precision)
 	if err != nil {
 		return 0, err
 	}
-	return Fixed8(num), err
-}
-
-// FixedNFromString parses s which must be a fixed point number
-// with precision 10^-d.
-func FixedNFromString(s string, precision int) (int64, error) {
-	parts := strings.SplitN(s, ".", 2)
-	d := int64(math.Pow10(precision))
-	ip, err := strconv.ParseInt(parts[0], 10, 64)
-	if err != nil {
-		return 0, errInvalidString
-	} else if len(parts) == 1 {
-		return ip * d, nil
-	}
-
-	fp, err := strconv.ParseInt(parts[1], 10, 64)
-	if err != nil || fp >= d {
-		return 0, errInvalidString
-	}
-	for i := len(parts[1]); i < precision; i++ {
-		fp *= 10
-	}
-	if ip < 0 {
-		return ip*d - fp, nil
-	}
-	return ip*d + fp, nil
+	return Fixed8(num.Int64()), err
 }
 
 // UnmarshalJSON implements the json unmarshaller interface.

pkg/encoding/fixedn/fixed8_test.go

@@ -8,7 +8,6 @@ import (
 
 	"github.com/nspcc-dev/neo-go/internal/testserdes"
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 	"gopkg.in/yaml.v2"
 )
 
@@ -85,20 +84,6 @@ func TestFixed8FromString(t *testing.T) {
 	assert.Error(t, err)
 }
 
-func TestFixedNFromString(t *testing.T) {
-	val := "123.456"
-	num, err := FixedNFromString(val, 3)
-	require.NoError(t, err)
-	require.EqualValues(t, 123456, num)
-
-	num, err = FixedNFromString(val, 4)
-	require.NoError(t, err)
-	require.EqualValues(t, 1234560, num)
-
-	_, err = FixedNFromString(val, 2)
-	require.Error(t, err)
-}
-
 func TestSatoshi(t *testing.T) {
 	satoshif8 := Satoshi()
 	assert.Equal(t, "0.00000001", satoshif8.String())