Converting 32 bit binary number to an IP address

This script will convert a 32-bit number into an IP address. This script is usually used by other TCP/IP scripts, not necessarily directly. This script also requires New-CmnLogEntry

Function ConvertTo-CmnCidr {
<#
.SYNOPSIS
Converts IP address and subnet mask to a CIDR address.DESCRIPTION
    Converts IP address and subnet mask in put to a CIDR address.
    This function als requires New-CmnLogEntry


.PARAMETER ipAddress
    IP Address in dotted decimal notation


.PARAMETER subnetMask
    Subnet mask in dotted decimal notation


.PARAMETER logFile
    File for writing logs to (default is C:\Windows\Temp\Error.log).


.PARAMETER logEntries
    Set to $true to write to the log file. Otherwise, it will just be New-CMNLogEntry -Entry (default is $false).


.PARAMETER maxLogSize
    Max size for the log (default is 5MB).


.PARAMETER maxLogHistory
    Specifies the number of history log files to keep (default is 5).

.EXAMPLE
    ConvertTo-CmnCidr -ipAddress 192.168.0.1 -subnetMask 255.255.240.0
    will return 192.168.0.1/20


.LINK
    http://configman-notes.com


.NOTES
    Author:     Jim Parris
    Email:      Jim@ConfigMan-Notes
    PSVer:      2.0/3.0
    Version:    1.0.0
    Date:       2018-12-26
    Updated:    2020-07-10 Cleanup/comment
#>

[CmdletBinding(ConfirmImpact = 'Low')]
Param(
    [Parameter(Mandatory = $true, ValueFromPipeline = $true, ValueFromPipelineByPropertyName = $true, HelpMessage = 'IP Address in dotted decimal notation')]
    [ValidatePattern('^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$')]
    [string]$ipAddress,

    [Parameter(Mandatory = $true, HelpMessage = 'Subnet mask in dotted decimal notation')]
    [ValidatePattern('^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$')]
    [String]$subnetMask,


    [Parameter(Mandatory = $false, HelpMessage = 'File for writing logs to (default is C:\Windows\Temp\Error.log).')]
    [String]$logFile = 'C:\Windows\Temp\Error.log',


    [Parameter(Mandatory = $false, HelpMessage = 'Set to $true to write to the log file. Otherwise, it will just be write-verbose (default is $false).')]
    [Boolean]$logEntries = $false,


    [Parameter(Mandatory = $false, HelpMessage = 'Max size for the log (default is 5MB).')]
    [Int]$maxLogSize = 5242880,


    [Parameter(Mandatory = $false, HelpMessage = 'Specifies the number of history log files to keep (default is 5).')]
    [Int]$maxLogHistory = 5
)


begin {
    #Build splat for log entries
    $NewLogEntry = @{
        logFile       = $logFile;
        component     = 'ConvertTo-CmnCidr';
        logEntries    = $logEntries;
        maxLogSize    = $MaxLogSize;
        maxLogHistory = $maxLogHistory;
    }


    # Log variables
    New-CMNLogEntry -entry 'Starting Function' -type 1 @NewLogEntry
    New-CMNLogEntry -entry "ipAddress = $ipAddress" -type 1 @NewLogEntry
    New-CMNLogEntry -entry "subnetMask = $subnetMask" -type 1 @NewLogEntry
    New-CMNLogEntry -entry "logFile = $logFile" -type 1 @NewLogEntry
    New-CMNLogEntry -entry "logEntries = $logEntries" -type 1 @NewLogEntry
    New-CMNLogEntry -entry "maxLogSize = $maxLogSize" -type 1 @NewLogEntry
    New-CMNLogEntry -entry "maxLogHistory = $maxLogHistory" -type 1 @NewLogEntry
}


process {
    New-CMNLogEntry -entry 'Beginning process loop' -type 1 @NewLogEntry
    # Get each octet seperate
    $octets = $subnetMask -split "\." 
    $subnetInBinary = @()


    # Let's convert the octets to binary
    foreach ($octet in $octets) { 
        # Convert to binary 
        $octetInBinary = [convert]::ToString($octet, 2) 
        # Get length of binary string add leading zeros to make octet 
        $octetInBinary = ("0" * (8 - ($octetInBinary).Length) + $octetInBinary) 
        # Add to variable
        $subnetInBinary = $subnetInBinary + $octetInBinary 
    } 
    $subnetInBinary = $subnetInBinary -join "" 
    New-CMNLogEntry -Entry "Subnet = $subnetInBinary" -type 1 @NewLogEntry


    # Now, let's make sure it's a valid subnet mask
    $x = 0
    while ($subnetInBinary.Substring($x, 1) -eq '1') {
        $x++
    }
    $networkBits = $x


    # OK, now we've got all the 1's, let's make sure the rest are 0's!
    do {
        if ($subnetInBinary.Substring($x, 1) -ne '0') {
            # No good, time to alert!
            $errorMessage = "The mask $subnetMask is invalid"
            New-CMNLogEntry -entry $errorMessage -type 3 @NewLogEntry
            throw $errorMessage
        } 
        $x++ 
    } while ($x -lt 32)
}


End {
    # Done! Log and send back the results
    $results = "$ipAddress/$networkBits"
    New-CMNLogEntry -entry "Returning $results" -type 1 @NewLogEntry
    New-CMNLogEntry -entry 'Completing Function' -type 1 @NewLogEntry
    Return $results
}
} #End ConvertTo-CmnCidr

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