Merge c31da0254a into 2b68c56fe0

* Adjust Ln method to prevent infinity iteration loops
* Add test case for infinity loop

decimal.go

@@ -129,11 +129,10 @@ func NewFromBigInt(value *big.Int, exp int32) Decimal {
 //
 // Example:
 //
-//     d1 := NewFromBigRat(big.NewRat(0, 1), 0)    // output: "0"
-//     d2 := NewFromBigRat(big.NewRat(4, 5), 1)    // output: "0.8"
-//     d3 := NewFromBigRat(big.NewRat(1000, 3), 3) // output: "333.333"
-//     d4 := NewFromBigRat(big.NewRat(2, 7), 4)    // output: "0.2857"
-//
+//	d1 := NewFromBigRat(big.NewRat(0, 1), 0)    // output: "0"
+//	d2 := NewFromBigRat(big.NewRat(4, 5), 1)    // output: "0.8"
+//	d3 := NewFromBigRat(big.NewRat(1000, 3), 3) // output: "333.333"
+//	d4 := NewFromBigRat(big.NewRat(2, 7), 4)    // output: "0.2857"
 func NewFromBigRat(value *big.Rat, precision int32) Decimal {
 	return Decimal{
 		value: new(big.Int).Set(value.Num()),
@@ -920,7 +919,10 @@ func (d Decimal) Ln(precision int32) (Decimal, error) {
 		// Halley's Iteration.
 		// Calculating n-th term of formula: a_(n+1) = a_n - 2 * (exp(a_n) - z) / (exp(a_n) + z),
 		// until the difference between current and next term is smaller than epsilon
-		for {
+		var prevStep Decimal
+		maxIters := calcPrecision*2 + 10
+
+		for i := int32(0); i < maxIters; i++ {
 			// exp(a_n)
 			comp3, _ = comp1.ExpTaylor(calcPrecision)
 			// exp(a_n) - z
@@ -934,9 +936,17 @@ func (d Decimal) Ln(precision int32) (Decimal, error) {
 			// comp1 = a_(n+1) = a_n - 2 * (exp(a_n) - z) / (exp(a_n) + z)
 			comp1 = comp1.Sub(comp3)
 
+			if prevStep.Add(comp3).IsZero() {
+				// If iteration steps oscillate we should return early and prevent an infinity loop
+				// NOTE(mwoss): This should be quite a rare case, returning error is not necessary
+				break
+			}
+
 			if comp3.Abs().Cmp(epsilon) <= 0 {
 				break
 			}
+
+			prevStep = comp3
 		}
 	}
 
@@ -1165,6 +1175,73 @@ func (d Decimal) String() string {
 	return d.string(true)
 }
 
+// Format formats a decimal.
+// thousandsSeparator can be empty, in which case the integer value will be displayed without separation.
+// if decimalSeparator is empty and the value is a decimal this will panic.
+func (d Decimal) Format(thousandsSeparator string, decimalSeparator string, trimTrailingZeros bool) string {
+	if d.exp >= 0 {
+		d = d.rescale(0)
+	}
+
+	abs := new(big.Int).Abs(d.value)
+	str := abs.String()
+
+	var intPart, fractionalPart string
+
+	// NOTE(vadim): this cast to int will cause bugs if d.exp == INT_MIN
+	// and you are on a 32-bit machine. Won't fix this super-edge case.
+	dExpInt := int(d.exp)
+	if len(str) > -dExpInt {
+		intPart = str[:len(str)+dExpInt]
+		fractionalPart = str[len(str)+dExpInt:]
+	} else {
+		intPart = "0"
+
+		num0s := -dExpInt - len(str)
+		fractionalPart = strings.Repeat("0", num0s) + str
+	}
+
+	if thousandsSeparator != "" {
+		parts := 1 + (len(intPart)-1)/3
+		if parts > 1 {
+			intParts := make([]string, 1+(len(intPart)-1)/3)
+			offset := len(intPart) - (len(intParts)-1)*3
+			for i := 0; i < len(intParts); i++ {
+				if i == 0 {
+					intParts[i] = intPart[0:offset]
+				} else {
+					intParts[i] = intPart[(i-1)*3+offset : i*3+offset]
+				}
+			}
+			intPart = strings.Join(intParts, thousandsSeparator)
+		}
+	}
+
+	if trimTrailingZeros {
+		i := len(fractionalPart) - 1
+		for ; i >= 0; i-- {
+			if fractionalPart[i] != '0' {
+				break
+			}
+		}
+		fractionalPart = fractionalPart[:i+1]
+	}
+	if fractionalPart != "" && decimalSeparator == "" {
+		panic("no decimal separator for non-integer")
+	}
+
+	number := intPart
+	if len(fractionalPart) > 0 {
+		number += decimalSeparator + fractionalPart
+	}
+
+	if d.value.Sign() < 0 {
+		return "-" + number
+	}
+
+	return number
+}
+
 // StringFixed returns a rounded fixed-point string with places digits after
 // the decimal point.
 //
@@ -1595,48 +1672,7 @@ func (d Decimal) StringScaled(exp int32) string {
 }
 
 func (d Decimal) string(trimTrailingZeros bool) string {
-	if d.exp >= 0 {
-		return d.rescale(0).value.String()
-	}
-
-	abs := new(big.Int).Abs(d.value)
-	str := abs.String()
-
-	var intPart, fractionalPart string
-
-	// NOTE(vadim): this cast to int will cause bugs if d.exp == INT_MIN
-	// and you are on a 32-bit machine. Won't fix this super-edge case.
-	dExpInt := int(d.exp)
-	if len(str) > -dExpInt {
-		intPart = str[:len(str)+dExpInt]
-		fractionalPart = str[len(str)+dExpInt:]
-	} else {
-		intPart = "0"
-
-		num0s := -dExpInt - len(str)
-		fractionalPart = strings.Repeat("0", num0s) + str
-	}
-
-	if trimTrailingZeros {
-		i := len(fractionalPart) - 1
-		for ; i >= 0; i-- {
-			if fractionalPart[i] != '0' {
-				break
-			}
-		}
-		fractionalPart = fractionalPart[:i+1]
-	}
-
-	number := intPart
-	if len(fractionalPart) > 0 {
-		number += "." + fractionalPart
-	}
-
-	if d.value.Sign() < 0 {
-		return "-" + number
-	}
-
-	return number
+	return d.Format("", ".", trimTrailingZeros)
 }
 
 func (d *Decimal) ensureInitialized() {

decimal_test.go

@@ -1513,6 +1513,47 @@ func TestDecimal_RoundDownAndStringFixed(t *testing.T) {
 	}
 }
 
+func TestDecimal_Format(t *testing.T) {
+	type testData struct {
+		input              string
+		thousandsSeparator string
+		decimalSeparator   string
+		trimTrailingZeros  bool
+		expected           string
+	}
+	tests := []testData{
+		{"0", ",", ".", false, "0"},
+		{"0", ",", ".", true, "0"},
+		{"999", ",", ".", true, "999"},
+		{"1000", ",", ".", true, "1,000"},
+		{"123", ",", ".", true, "123"},
+		{"1234", ",", ".", true, "1,234"},
+		{"12345.67", "", ".", true, "12345.67"},
+		{"12345.00", ",", ".", true, "12,345"},
+		{"12345.00", ",", ".", false, "12,345.00"},
+		{"123456.00", ",", ".", false, "123,456.00"},
+		{"1234567.00", ",", ".", false, "1,234,567.00"},
+		{"1234567.00", ".", ",", false, "1.234.567,00"},
+		{"1234567.00", "_", ".", true, "1_234_567"},
+		{"-12.00", "_", ".", true, "-12"},
+		{"-123.00", "_", ".", true, "-123"},
+		{"-1234.00", "_", ".", true, "-1_234"},
+	}
+
+	for _, test := range tests {
+		d, err := NewFromString(test.input)
+		if err != nil {
+			panic(err)
+		}
+
+		got := d.Format(test.thousandsSeparator, test.decimalSeparator, test.trimTrailingZeros)
+		if got != test.expected {
+			t.Errorf("Format %s got %s, expected %s",
+				d, got, test.expected)
+		}
+	}
+}
+
 func TestDecimal_BankRoundAndStringFixed(t *testing.T) {
 	type testData struct {
 		input         string
@@ -2822,6 +2863,7 @@ func TestDecimal_Ln(t *testing.T) {
 		{"839101.0351094726488848490572028502", 50, "13.64008640145229044389152437468283605382056561604272"},
 		{"5023583755703750094849.03519358513093500275017501750602739169823", 25, "49.9684305274348922267409953"},
 		{"5023583755703750094849.03519358513093500275017501750602739169823", -1, "50.0"},
+		{"66.12", 18, "4.191471272952823429"},
 	} {
 		d, _ := NewFromString(testCase.Dec)
 		expected, _ := NewFromString(testCase.Expected)