tpl: Add math.Ceil, Floor, and Round

Ceil and Floor are frontends for the stdlib math functions. The Round
implementation is essentially the same thing except that the Go stdlib
doesn't include a Round implementation in a stable release yet.  I've
included the Round function slated for Go 1.10.

Fixes #3883

tpl/math/math.go

@@ -34,11 +34,31 @@ func (ns *Namespace) Add(a, b interface{}) (interface{}, error) {
 	return DoArithmetic(a, b, '+')
 }
 
+// Ceil returns the least integer value greater than or equal to x.
+func (ns *Namespace) Ceil(x interface{}) (float64, error) {
+	xf, err := cast.ToFloat64E(x)
+	if err != nil {
+		return 0, errors.New("Ceil operator can't be used with non-float value")
+	}
+
+	return math.Ceil(xf), nil
+}
+
 // Div divides two numbers.
 func (ns *Namespace) Div(a, b interface{}) (interface{}, error) {
 	return DoArithmetic(a, b, '/')
 }
 
+// Floor returns the greatest integer value less than or equal to x.
+func (ns *Namespace) Floor(x interface{}) (float64, error) {
+	xf, err := cast.ToFloat64E(x)
+	if err != nil {
+		return 0, errors.New("Floor operator can't be used with non-float value")
+	}
+
+	return math.Floor(xf), nil
+}
+
 // Log returns the natural logarithm of a number.
 func (ns *Namespace) Log(a interface{}) (float64, error) {
 	af, err := cast.ToFloat64E(a)
@@ -92,6 +112,16 @@ func (ns *Namespace) Mul(a, b interface{}) (interface{}, error) {
 	return DoArithmetic(a, b, '*')
 }
 
+// Round returns the nearest integer, rounding half away from zero.
+func (ns *Namespace) Round(x interface{}) (float64, error) {
+	xf, err := cast.ToFloat64E(x)
+	if err != nil {
+		return 0, errors.New("Round operator can't be used with non-float value")
+	}
+
+	return _round(xf), nil
+}
+
 // Sub subtracts two numbers.
 func (ns *Namespace) Sub(a, b interface{}) (interface{}, error) {
 	return DoArithmetic(a, b, '-')