Truncating vs. Rounding in go

round.go

// http://play.golang.org/p/KNhgeuU5sT
package main

import (
	"fmt"
	"math"
)

// truncate a float to two levels of precision
func Truncate(some float64) float64 {
	return float64(int(some * 100)) / 100
}

func Round(val float64, roundOn float64, places int) float64 {

	pow := math.Pow(10, float64(places))
	digit := pow * val
	_, div := math.Modf(digit)

	var round float64
	if val > 0 {
		if div >= roundOn {
			round = math.Ceil(digit)
		} else {
			round = math.Floor(digit)
		}
	} else {
		if div >= roundOn {
			round = math.Floor(digit)
		} else {
			round = math.Ceil(digit)
		}
	}

	return round / pow
}

func RoundPrice(price float64) float64 {
	return Round(price, 0.5, 2)
}

func main() {
	floatTests := []float64{
		10 / 3.0,
		-10 / 3.0,
		-38.288888,
	}

	fmt.Println("original", "truncated", "rounded")
	for _, k := range floatTests {
		t := Truncate(k)
		r := RoundPrice(k)
		fmt.Println(k, t, r)
	}
}