Add Float#round method.

vm/float.go

@@ -462,6 +462,43 @@ func builtinFloatInstanceMethods() []*BuiltinMethodObject {
 				}
 			},
 		},
+		{
+			//  Rounds float to a given precision in decimal digits (default 0 digits)
+			//
+			// ```Ruby
+			// 1.115.round  # => 1
+			// 1.115.round(1)  # => 1.1
+			// 1.115.round(2)  # => 1.12
+			// -1.115.round  # => -1
+			// -1.115.round(1)  # => -1.1
+			// -1.115.round(2)  # => -1.12
+			// ```
+			// @return [Integer]
+			Name: "round",
+			Fn: func(receiver Object, sourceLine int) builtinMethodBody {
+				return func(t *thread, args []Object, blockFrame *normalCallFrame) Object {
+					var precision int
+
+					if len(args) > 1 {
+						return t.vm.initErrorObject(errors.ArgumentError, sourceLine, "Expect 0 or 1 argument. got=%v", strconv.Itoa(len(args)))
+					} else if len(args) == 1 {
+						int, ok := args[0].(*IntegerObject)
+
+						if !ok {
+							return t.vm.initErrorObject(errors.TypeError, sourceLine, errors.WrongArgumentTypeFormat, classes.IntegerClass, args[0].Class().Name)
+						}
+
+						precision = int.value
+					}
+
+
+					f := receiver.(*FloatObject).floatValue()
+					n := math.Pow10(precision)
+
+					return t.vm.initFloatObject(math.Round(f*n)/n)
+				}
+			},
+		},
 		{
 			// Returns true if Float is less than 0.0
 			//

vm/float_test.go

@@ -365,6 +365,30 @@ func TestFloatPositive(t *testing.T) {
 	}
 }
 
+func TestFloatRound(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected interface{}
+	}{
+		{"1.115.round", 1.0},
+		{"1.115.round(1)", 1.1},
+		{"1.115.round(2)", 1.12},
+		{"-1.115.round", -1.0},
+		{"-1.115.round(1)", -1.1},
+		{"-1.115.round(2)", -1.12},
+		{"1.115.round(-1)", 0.0},
+		{"-1.115.round(-1)", 0.0},
+	}
+
+	for i, tt := range tests {
+		v := initTestVM()
+		evaluated := v.testEval(t, tt.input, getFilename())
+		verifyExpected(t, i, evaluated, tt.expected)
+		v.checkCFP(t, i, 0)
+		v.checkSP(t, i, 1)
+	}
+}
+
 func TestFloatZero(t *testing.T) {
 	tests := []struct {
 		input    string