Added Banker Rounding (#61)

* made GTE/GT/LT/LTE go-lint compliant

* added banker rounding and tests (RoundBank, StringFixedBank)

2 files changed, 137 insertions, 4 deletions

diff --git a/decimal.go b/decimal.go
index 17c8d72..1729b61 100644
--- a/decimal.go
+++ b/decimal.go
@@ -431,23 +431,23 @@ func (d Decimal) Equals(d2 Decimal) bool {
 	return d.Equal(d2)
 }
 
-// Greater Than (GT) returns true when d is greater than d2.
+// GreaterThan (GT) returns true when d is greater than d2.
 func (d Decimal) GreaterThan(d2 Decimal) bool {
 	return d.Cmp(d2) == 1
 }
 
-// Greater Than or Equal (GTE) returns true when d is greater than or equal to d2.
+// GreaterThanOrEqual (GTE) returns true when d is greater than or equal to d2.
 func (d Decimal) GreaterThanOrEqual(d2 Decimal) bool {
 	cmp := d.Cmp(d2)
 	return cmp == 1 || cmp == 0
 }
 
-// Less Than (LT) returns true when d is less than d2.
+// LessThan (LT) returns true when d is less than d2.
 func (d Decimal) LessThan(d2 Decimal) bool {
 	return d.Cmp(d2) == -1
 }
 
-// Less Than or Equal (LTE) returns true when d is less than or equal to d2.
+// LessThanOrEqual (LTE) returns true when d is less than or equal to d2.
 func (d Decimal) LessThanOrEqual(d2 Decimal) bool {
 	cmp := d.Cmp(d2)
 	return cmp == -1 || cmp == 0
@@ -539,6 +539,24 @@ func (d Decimal) StringFixed(places int32) string {
 	return rounded.string(false)
 }
 
+// StringFixedBank returns a banker rounded fixed-point string with places digits
+// after the decimal point.
+//
+// Example:
+//
+// 	   NewFromFloat(0).StringFixed(2) // output: "0.00"
+// 	   NewFromFloat(0).StringFixed(0) // output: "0"
+// 	   NewFromFloat(5.45).StringFixed(0) // output: "5"
+// 	   NewFromFloat(5.45).StringFixed(1) // output: "5.4"
+// 	   NewFromFloat(5.45).StringFixed(2) // output: "5.45"
+// 	   NewFromFloat(5.45).StringFixed(3) // output: "5.450"
+// 	   NewFromFloat(545).StringFixed(-1) // output: "550"
+//
+func (d Decimal) StringFixedBank(places int32) string {
+	rounded := d.RoundBank(places)
+	return rounded.string(false)
+}
+
 // Round rounds the decimal to places decimal places.
 // If places < 0, it will round the integer part to the nearest 10^(-places).
 //
@@ -568,6 +586,37 @@ func (d Decimal) Round(places int32) Decimal {
 	return ret
 }
 
+// RoundBank rounds the decimal to places decimal places.
+// If the final digit to round is equidistant from the nearest two integers the
+// rounded value is taken as the even number
+//
+// If places < 0, it will round the integer part to the nearest 10^(-places).
+//
+// Examples:
+//
+// 	   NewFromFloat(5.45).Round(1).String() // output: "5.4"
+// 	   NewFromFloat(545).Round(-1).String() // output: "540"
+// 	   NewFromFloat(5.46).Round(1).String() // output: "5.5"
+// 	   NewFromFloat(546).Round(-1).String() // output: "550"
+// 	   NewFromFloat(5.55).Round(1).String() // output: "5.6"
+// 	   NewFromFloat(555).Round(-1).String() // output: "560"
+//
+func (d Decimal) RoundBank(places int32) Decimal {
+
+	round := d.Round(places)
+	remainder := d.Sub(round).Abs()
+
+	if remainder.value.Cmp(fiveInt) == 0 && round.value.Bit(0) != 0 {
+		if round.value.Sign() < 0 {
+			round.value.Add(round.value, oneInt)
+		} else {
+			round.value.Sub(round.value, oneInt)
+		}
+	}
+
+	return round
+}
+
 // Floor returns the nearest integer value less than or equal to d.
 func (d Decimal) Floor() Decimal {
 	d.ensureInitialized()
diff --git a/decimal_test.go b/decimal_test.go
index fc9cb12..d606dc9 100644
--- a/decimal_test.go
+++ b/decimal_test.go
@@ -550,6 +550,90 @@ func TestDecimal_RoundAndStringFixed(t *testing.T) {
 	}
 }
 
+func TestDecimal_BankRoundAndStringFixed(t *testing.T) {
+	type testData struct {
+		input         string
+		places        int32
+		expected      string
+		expectedFixed string
+	}
+	tests := []testData{
+		{"1.454", 0, "1", ""},
+		{"1.454", 1, "1.5", ""},
+		{"1.454", 2, "1.45", ""},
+		{"1.454", 3, "1.454", ""},
+		{"1.454", 4, "1.454", "1.4540"},
+		{"1.454", 5, "1.454", "1.45400"},
+		{"1.554", 0, "2", ""},
+		{"1.554", 1, "1.6", ""},
+		{"1.554", 2, "1.55", ""},
+		{"0.554", 0, "1", ""},
+		{"0.454", 0, "0", ""},
+		{"0.454", 5, "0.454", "0.45400"},
+		{"0", 0, "0", ""},
+		{"0", 1, "0", "0.0"},
+		{"0", 2, "0", "0.00"},
+		{"0", -1, "0", ""},
+		{"5", 2, "5", "5.00"},
+		{"5", 1, "5", "5.0"},
+		{"5", 0, "5", ""},
+		{"500", 2, "500", "500.00"},
+		{"545", -2, "500", ""},
+		{"545", -3, "1000", ""},
+		{"545", -4, "0", ""},
+		{"499", -3, "0", ""},
+		{"499", -4, "0", ""},
+		{"1.45", 1, "1.4", ""},
+		{"1.55", 1, "1.6", ""},
+		{"1.65", 1, "1.6", ""},
+		{"545", -1, "540", ""},
+		{"565", -1, "560", ""},
+		{"555", -1, "560", ""},
+	}
+
+	// add negative number tests
+	for _, test := range tests {
+		expected := test.expected
+		if expected != "0" {
+			expected = "-" + expected
+		}
+		expectedStr := test.expectedFixed
+		if strings.ContainsAny(expectedStr, "123456789") && expectedStr != "" {
+			expectedStr = "-" + expectedStr
+		}
+		tests = append(tests,
+			testData{"-" + test.input, test.places, expected, expectedStr})
+	}
+
+	for _, test := range tests {
+		d, err := NewFromString(test.input)
+		if err != nil {
+			panic(err)
+		}
+
+		// test Round
+		expected, err := NewFromString(test.expected)
+		if err != nil {
+			panic(err)
+		}
+		got := d.RoundBank(test.places)
+		if !got.Equal(expected) {
+			t.Errorf("Bank Rounding %s to %d places, got %s, expected %s",
+				d, test.places, got, expected)
+		}
+
+		// test StringFixed
+		if test.expectedFixed == "" {
+			test.expectedFixed = test.expected
+		}
+		gotStr := d.StringFixedBank(test.places)
+		if gotStr != test.expectedFixed {
+			t.Errorf("(%s).StringFixed(%d): got %s, expected %s",
+				d, test.places, gotStr, test.expectedFixed)
+		}
+	}
+}
+
 func TestDecimal_Uninitialized(t *testing.T) {
 	a := Decimal{}
 	b := Decimal{}