FIX: fix format string float point issue

pkg/fixedpoint/convert.go

@@ -115,9 +115,50 @@ func (v Value) FormatString(prec int) string {
 	} else if v == NegInf {
 		return "-inf"
 	}
-	pow := math.Pow10(prec)
-	return strconv.FormatFloat(
-		math.Trunc(float64(v)/DefaultPow*pow)/pow, 'f', prec, 64)
+
+	u := int64(v)
+
+	// trunc precision
+	precDiff := DefaultPrecision - prec
+	if precDiff > 0 {
+		powDiff := int64(math.Pow10(precDiff))
+		u = int64(v) / powDiff * powDiff
+	}
+
+	// check sign
+	sign := Value(u).Sign()
+
+	basePow := int64(DefaultPow)
+	a := u / basePow
+	b := u % basePow
+
+	if a < 0 {
+		a = -a
+	}
+
+	if b < 0 {
+		b = -b
+	}
+
+	str := strconv.FormatInt(a, 10)
+	if prec > 0 {
+		bStr := fmt.Sprintf(".%08d", b)
+		if prec <= DefaultPrecision {
+			bStr = bStr[0 : prec+1]
+		} else {
+			for i := prec - DefaultPrecision; i > 0; i-- {
+				bStr += "0"
+			}
+		}
+
+		str += bStr
+	}
+
+	if sign < 0 {
+		str = "-" + str
+	}
+
+	return str
 }
 
 func (v Value) Percentage() string {

pkg/fixedpoint/convert_test.go

@@ -0,0 +1,59 @@
+package fixedpoint
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_FormatString(t *testing.T) {
+	assert := assert.New(t)
+
+	t.Run("Value(57000000) with prec = 5, expected 0.57", func(t *testing.T) {
+		v := Value(57000000)
+		s := v.FormatString(5)
+		assert.Equal("0.57000", s)
+	})
+
+	t.Run("Value(57123456) with prec = 5, expected 0.57123", func(t *testing.T) {
+		v := Value(57123456)
+		s := v.FormatString(5)
+		assert.Equal("0.57123", s)
+	})
+
+	t.Run("Value(123456789) with prec = 9, expected 1.23456789", func(t *testing.T) {
+		v := Value(123456789)
+		s := v.FormatString(9)
+		assert.Equal("1.234567890", s)
+	})
+
+	t.Run("Value(102345678) with prec = 9, expected 1.02345678", func(t *testing.T) {
+		v := Value(102345678)
+		s := v.FormatString(9)
+		assert.Equal("1.023456780", s)
+	})
+
+	t.Run("Value(-57000000) with prec = 5, expected -0.57", func(t *testing.T) {
+		v := Value(-57000000)
+		s := v.FormatString(5)
+		assert.Equal("-0.57000", s)
+	})
+
+	t.Run("Value(-123456789) with prec = 9, expected 1.23456789", func(t *testing.T) {
+		v := Value(-123456789)
+		s := v.FormatString(9)
+		assert.Equal("-1.234567890", s)
+	})
+
+	t.Run("Value(1234567890) with prec = -1, expected 10", func(t *testing.T) {
+		v := Value(1234567890)
+		s := v.FormatString(-1)
+		assert.Equal("10", s)
+	})
+
+	t.Run("Value(-1234) with prec = 3, expected = 0.000", func(t *testing.T) {
+		v := Value(-1234)
+		s := v.FormatString(3)
+		assert.Equal("0.000", s)
+	})
+}

pkg/types/market.go

@@ -113,7 +113,7 @@ func (m Market) FormatPrice(val fixedpoint.Value) string {
 }
 
 func FormatPrice(price fixedpoint.Value, tickSize fixedpoint.Value) string {
-	prec := int(math.Round(math.Abs(math.Log10(tickSize.Float64()))))
+	prec := int(math.Round(math.Log10(tickSize.Float64()) * -1.0))
 	return price.FormatString(prec)
 }