[mathutil] Add method 'FromPerc'

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### [13.5.1](https://kaos.sh/ek/13.5.1)
 
+- `[mathutil]` Added method `FromPerc`
 - `[mathutil]` Code refactoring
 
 ### [13.5.0](https://kaos.sh/ek/13.5.0)

mathutil/example_test.go

@@ -83,6 +83,12 @@ func ExamplePerc() {
 	// 30%
 }
 
+func ExampleFromPerc() {
+	fmt.Printf("%g\n", FromPerc(15.0, 2860))
+	// Output:
+	// 429
+}
+
 func ExampleRound() {
 	fmt.Println(Round(3.14159, 2))
 	// Output:

mathutil/mathutil.go

@@ -130,6 +130,15 @@ func Perc[N Numeric](current, total N) float64 {
 	return (float64(current) / float64(total)) * 100.0
 }
 
+// FromPerc calculates value from percentage
+func FromPerc(perc float64, total float64) float64 {
+	if perc <= 0 || total == 0 {
+		return 0
+	}
+
+	return (total / 100.0) * perc
+}
+
 // Round returns rounded value
 func Round(v float64, p int) float64 {
 	pow := math.Pow(10, float64(p))

mathutil/mathutil_test.go

@@ -68,3 +68,11 @@ func (s *MathUtilSuite) TestPerc(c *C) {
 	c.Assert(Perc(100, 100), Equals, 100.0)
 	c.Assert(Perc(200, 100), Equals, 200.0)
 }
+
+func (s *MathUtilSuite) TestFromPerc(c *C) {
+	c.Assert(FromPerc(0, 0), Equals, 0.0)
+	c.Assert(FromPerc(100, 0), Equals, 0.0)
+	c.Assert(FromPerc(-1, 1000), Equals, 0.0)
+	c.Assert(FromPerc(250, 100), Equals, 250.0)
+	c.Assert(FromPerc(25.55, -100), Equals, -25.55)
+}