Merge 6e54f647f0 into d00399e161

decimal.go

@@ -51,6 +51,14 @@ var DivisionPrecision = 16
 // silently lose precision.
 var MarshalJSONWithoutQuotes = false
 
+// StringTrimTrailingZeros should be set to false if you want the decimal stringify without zeros trailing.
+// By default, when decimal is output as a string (for example, in JSON), zeros are truncated from it (2.00 -> 2, 3.11 -> 3.11, 13.000 -> 13).
+// But this logic can be changed by this variable.
+// For example, if you have numeric(10,2) values stored in your database,
+// and you want your API response to always be given 2 decimal places (even 2.00, 3.00, 17.00 [not 2,3,17]),
+// then this variable is a great way out.
+var StringTrimTrailingZeros = true
+
 // ExpMaxIterations specifies the maximum number of iterations needed to calculate
 // precise natural exponent value using ExpHullAbrham method.
 var ExpMaxIterations = 1000
@@ -124,6 +132,26 @@ func NewFromBigInt(value *big.Int, exp int32) Decimal {
 	}
 }
 
+// NewFromBigRat returns a new Decimal from a big.Rat. The numerator and
+// denominator are divided and rounded to the given precision.
+//
+// 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"
+//
+func NewFromBigRat(value *big.Rat, precision int32) Decimal {
+	return Decimal{
+		value: new(big.Int).Set(value.Num()),
+		exp:   0,
+	}.DivRound(Decimal{
+		value: new(big.Int).Set(value.Denom()),
+		exp:   0,
+	}, precision)
+}
+
 // NewFromString returns a new Decimal from a string representation.
 // Trailing zeroes are not trimmed.
 //
@@ -1142,7 +1170,7 @@ func (d Decimal) InexactFloat64() float64 {
 //
 //	-12.345
 func (d Decimal) String() string {
-	return d.string(true)
+	return d.string(StringTrimTrailingZeros)
 }
 
 // StringFixed returns a rounded fixed-point string with places digits after

decimal_test.go

@@ -556,6 +556,51 @@ func TestNewFromBigIntWithExponent(t *testing.T) {
 	}
 }
 
+func TestNewFromBigRat(t *testing.T) {
+	mustParseRat := func(val string) *big.Rat {
+		num, _ := new(big.Rat).SetString(val)
+		return num
+	}
+
+	type Inp struct {
+		val  *big.Rat
+		prec int32
+	}
+
+	tests := map[Inp]string{
+		Inp{big.NewRat(0, 1), 16}:                                                     "0",
+		Inp{big.NewRat(4, 5), 16}:                                                     "0.8",
+		Inp{big.NewRat(10, 2), 16}:                                                    "5",
+		Inp{big.NewRat(1023427554493, 43432632), 16}:                                  "23563.5628642767953828", // rounded
+		Inp{big.NewRat(1, 434324545566634), 16}:                                       "0.0000000000000023",
+		Inp{big.NewRat(1, 3), 16}:                                                     "0.3333333333333333",
+		Inp{big.NewRat(2, 3), 2}:                                                      "0.67",               // rounded
+		Inp{big.NewRat(2, 3), 16}:                                                     "0.6666666666666667", // rounded
+		Inp{big.NewRat(10000, 3), 16}:                                                 "3333.3333333333333333",
+		Inp{mustParseRat("30702832066636633479"), 16}:                                 "30702832066636633479",
+		Inp{mustParseRat("487028320159896636679.1827512895753"), 16}:                  "487028320159896636679.1827512895753",
+		Inp{mustParseRat("127028320612589896636633479.173582751289575278357832"), -2}: "127028320612589896636633500",                  // rounded
+		Inp{mustParseRat("127028320612589896636633479.173582751289575278357832"), 16}: "127028320612589896636633479.1735827512895753", // rounded
+		Inp{mustParseRat("127028320612589896636633479.173582751289575278357832"), 32}: "127028320612589896636633479.173582751289575278357832",
+	}
+
+	// add negatives
+	for p, s := range tests {
+		if p.val.Cmp(new(big.Rat)) > 0 {
+			tests[Inp{p.val.Neg(p.val), p.prec}] = "-" + s
+		}
+	}
+
+	for input, s := range tests {
+		d := NewFromBigRat(input.val, input.prec)
+		if d.String() != s {
+			t.Errorf("expected %s, got %s (%s, %d)",
+				s, d.String(),
+				d.value.String(), d.exp)
+		}
+	}
+}
+
 func TestCopy(t *testing.T) {
 	origin := New(1, 0)
 	cpy := origin.Copy()
@@ -3407,3 +3452,48 @@ func ExampleNewFromFloat() {
 	//0.123123123123123
 	//-10000000000000
 }
+
+func TestDecimal_String(t *testing.T) {
+	type testData struct {
+		input string
+		expected string
+	}
+
+	tests := []testData{
+		{"1.22", "1.22"},
+		{"1.00", "1"},
+		{"153.192", "153.192"},
+		{"999.999", "999.999"},
+		{"0.0000000001", "0.0000000001"},
+		{"0.0000000000", "0"},
+	}
+
+	for _, test := range tests {
+		d, err := NewFromString(test.input);
+		if err != nil {
+			t.Fatal(err)
+		} else if d.String() != test.expected {
+			t.Errorf("expected %s, got %s", test.expected, d.String())
+		}
+	}
+
+	defer func() {
+		StringTrimTrailingZeros = true
+	}()
+
+	StringTrimTrailingZeros = false
+	tests = []testData{
+		{"1.00", "1.00"},
+		{"0.00", "0.00"},
+		{"129.123000", "129.123000"},
+	}
+
+	for _, test := range tests {
+		d, err := NewFromString(test.input);
+		if err != nil {
+			t.Fatal(err)
+		} else if d.String() != test.expected {
+			t.Errorf("expected %s, got %s", test.expected, d.String())
+		}
+	}
+}