round.go - Round a float64 in Go

round.go

package main

func RoundPrec(x float64, prec int) float64 {
	if math.IsNaN(x) || math.IsInf(x, 0) {
		return x
	}

	sign := 1.0
	if x < 0 {
		sign = -1
		x *= -1
	}

	var rounder float64
	pow := math.Pow(10, float64(prec))
	intermed := x * pow
	_, frac := math.Modf(intermed)

	if frac >= 0.5 {
		rounder = math.Ceil(intermed)
	} else {
		rounder = math.Floor(intermed)
	}

	return rounder / pow * sign
}