Merge pull request #4 from EtienneBruines/master

Improved PowInt for performance by adding recursion

Author: unknwon

math.go

@@ -14,11 +14,16 @@
 
 package com
 
-// PowInt is int type of math.Pow function.
+// PowInt is int type of math.Pow function. 
 func PowInt(x int, y int) int {
-	num := 1
-	for i := 0; i < y; i++ {
-		num *= x
+	if y <= 0 {
+		return 1
+	} else {
+		if y % 2 == 0 {
+			sqrt := PowInt(x, y/2)
+			return sqrt * sqrt
+		} else {
+			return PowInt(x, y-1) * x
+		}
 	}
-	return num
 }

math_test.go

@@ -0,0 +1,42 @@
+// Copyright 2014 com authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License"): you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations
+// under the License.
+
+package com
+
+import (
+	"testing"
+	"math"
+	"math/rand"
+)
+
+func TestPow(t *testing.T) {
+	for x := 0; x < 10; x++ {
+		for y := 0; y < 8; y++ {
+			result := PowInt(x, y)
+			result_float := math.Pow(float64(x), float64(y))
+			if result != int(result_float) {
+				t.Errorf("Unable to correctly compute %d to the power of %d. Expected: %d, got %d. ", x, y, int(result_float), result)
+			}
+		}
+	}
+}
+
+func BenchmarkPow(b *testing.B) {
+	x := rand.Intn(100)
+	y := rand.Intn(6)
+	b.ResetTimer()
+	for n := 0; n < b.N; n++ {
+		PowInt(x, y)
+	}
+}