ipnet.go

package ipnet

var (
	// these allow zero-allocation IP masking
	cidrMasksIPv4 = [33]net.IPMask{}
	cidrMasksIPv6 = [129]net.IPMask{}
)

func init() {
	for i := 0; i <= 32; i++ {
		cidrMasksIPv4[i] = net.CIDRMask(i, net.IPv4len*8)
	}
	for i := 0; i <= 128; i++ {
		cidrMasksIPv6[i] = net.CIDRMask(i, net.IPv6len*8)
	}
}

// IPMask is a zero-allocation net.IPMask that _must_ be treated as immutable.
func IPMask(ones, bits int) net.IPMask {
	switch {
	case ones <= 32 && bits == net.IPv4len*8:
		return cidrMasksIPv4[ones]
	case ones <= 128 && bits == net.IPv6len*8:
		return cidrMasksIPv6[ones]
	default:
		return net.CIDRMask(ones, bits)
	}
}