function Test-Subnet ([string]$cidr, [string]$ip)
{
    $network, [int]$subnetlen = $cidr.Split('/')
    $a = [uint32[]]$network.split('.')
    [uint32] $unetwork = ($a[0] -shl 24) + ($a[1] -shl 16) + ($a[2] -shl 8) + $a[3]

    $mask = (-bnot [uint32]0) -shl (32 - $subnetlen)

    $a = [uint32[]]$ip.split('.')
    [uint32] $uip = ($a[0] -shl 24) + ($a[1] -shl 16) + ($a[2] -shl 8) + $a[3]

    $unetwork -eq ($mask -band $uip)
}