func arithRound(a *big.Float) (*big.Float, error) {
var i *big.Int
if a.Signbit() {
i, _ = new(big.Float).Sub(a, halfAwayFromZero).Int(nil)
} else {
i, _ = new(big.Float).Add(a, halfAwayFromZero).Int(nil)
}
return new(big.Float).SetInt(i), nil
}