lang: funcs: Add a mod function to the math package

This should make flip-flop functions easy to write.

lang/funcs/core/math/mod_func.go

@@ -0,0 +1,78 @@
+// Mgmt
+// Copyright (C) 2013-2019+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package coremath
+
+import (
+	"fmt"
+	"math"
+
+	"github.com/purpleidea/mgmt/lang/funcs/simplepoly"
+	"github.com/purpleidea/mgmt/lang/types"
+)
+
+func init() {
+	simplepoly.ModuleRegister(moduleName, "mod", []*types.FuncValue{
+		{
+			T: types.NewType("func(int, int) int"),
+			V: Mod,
+		},
+		{
+			T: types.NewType("func(float, float) float"),
+			V: Mod,
+		},
+	})
+}
+
+// Mod returns mod(x, y), the remainder of x/y. The two values must be either
+// both of KindInt or both of KindFloat, and it will return the same kind. If
+// you pass in a divisor of zero, this will error, eg: mod(x, 0) = NaN.
+// TODO: consider returning zero instead of erroring?
+func Mod(input []types.Value) (types.Value, error) {
+	var x, y float64
+	var float bool
+	k := input[0].Type().Kind
+	switch k {
+	case types.KindFloat:
+		float = true
+		x = input[0].Float()
+		y = input[1].Float()
+	case types.KindInt:
+		x = float64(input[0].Int())
+		y = float64(input[1].Int())
+	default:
+		return nil, fmt.Errorf("unexpected kind: %s", k)
+	}
+	z := math.Mod(x, y)
+	if math.IsNaN(z) {
+		return nil, fmt.Errorf("result is not a number")
+	}
+	if math.IsInf(z, 1) {
+		return nil, fmt.Errorf("unexpected positive infinity")
+	}
+	if math.IsInf(z, -1) {
+		return nil, fmt.Errorf("unexpected negative infinity")
+	}
+	if float {
+		return &types.FloatValue{
+			V: z,
+		}, nil
+	}
+	return &types.IntValue{
+		V: int64(z), // XXX: does this truncate?
+	}, nil
+}