CRC CALCULATOR - C# / POWERSHELL
CRC stands for Cyclic Redundancy Check. It is an error-detecting code used to determine if a block of data has been corrupted. CRC is a great technique for detecting common transmission errors. The receiving device also calculates the CRC and compares it to the CRC from the sending device. If even one bit in the message is received incorrectly, the CRCs will be different and an error will result.
I initially made this because the Get-Filehash was slow for big files, and some CRC implementation below are faster, some are slower.
Pure CRC PowerShell Implementation
function Get-CRC32 {
<#
.SYNOPSIS
Calculate CRC.
.DESCRIPTION
This function calculates the CRC of the input data using the CRC32 algorithm.
For a Test File, this CRC for a file length 349.83 MB (366819792 bytes): 157.39 seconds
.EXAMPLE
Get-CRC32 $data
.EXAMPLE
$data | Get-CRC32
.INPUTS
byte[]
.OUTPUTS
uint32
#>
[CmdletBinding(SupportsShouldProcess)]
param (
# Array of Bytes to use for CRC calculation
[Parameter(Mandatory=$true, Position = 0)]
[ValidateNotNullOrEmpty()]
[byte[]]$Bytes
)
Begin {
function New-CrcTable {
[uint32]$c = $null
$crcTable = New-Object 'System.Uint32[]' 256
for ($n = 0; $n -lt 256; $n++) {
$c = [uint32]$n
for ($k = 0; $k -lt 8; $k++) {
if ($c -band 1) {
$c = (0xEDB88320 -bxor ($c -shr 1))
}
else {
$c = ($c -shr 1)
}
}
$crcTable[$n] = $c
}
Write-Output $crcTable
}
function Update-Crc ([uint32]$crc, [byte[]]$buffer, [int]$length) {
[uint32]$c = $crc
if (-not($script:crcTable)) {
Write-Verbose "[Update-Crc] New-CrcTable start"
$script:crcTable = New-CrcTable
Write-Verbose "[Update-Crc] New-CrcTable done"
}
Write-Verbose "[Update-Crc] start ($length bytes)"
for ($n = 0; $n -lt $length; $n++) {
$c = ($script:crcTable[($c -bxor $buffer[$n]) -band 0xFF]) -bxor ($c -shr 8)
}
Write-Verbose "[Update-Crc] done"
Write-output $c
}
}
process{
try{
Write-Verbose "[Get-CRC32] clone data"
[byte[]]$dataArray = $Bytes.Clone()
[uint32]$inputLength = $dataArray.Length
Write-Verbose "[Get-CRC32] Update-Crc (len $inputLength bytes)"
[uint32]$tmp_crc_buf = Update-Crc –crc 0xffffffffL –buffer $dataArray –length $inputLength
[uint32]$crc_value = ($tmp_crc_buf -bxor 0xffffffffL)
Write-output $crc_value
}catch{
Write-Error "$_"
}
}
}
C# Implementation
Here’s a C# Implementation integrated in the PowerShell script
using System;
public static class ModRTU_CRC
{
public static readonly ushort[] CRCTable =
{
0X0000, 0XC0C1, 0XC181, 0X0140, 0XC301, 0X03C0, 0X0280, 0XC241, 0XC601, 0X06C0,
0X0780, 0XC741, 0X0500, 0XC5C1, 0XC481, 0X0440, 0XCC01, 0X0CC0, 0X0D80, 0XCD41,
0X0F00, 0XCFC1, 0XCE81, 0X0E40, 0X0A00, 0XCAC1, 0XCB81, 0X0B40, 0XC901, 0X09C0,
0X0880, 0XC841, 0XD801, 0X18C0, 0X1980, 0XD941, 0X1B00, 0XDBC1, 0XDA81, 0X1A40,
0X1E00, 0XDEC1, 0XDF81, 0X1F40, 0XDD01, 0X1DC0, 0X1C80, 0XDC41, 0X1400, 0XD4C1,
0XD581, 0X1540, 0XD701, 0X17C0, 0X1680, 0XD641, 0XD201, 0X12C0, 0X1380, 0XD341,
0X1100, 0XD1C1, 0XD081, 0X1040, 0XF001, 0X30C0, 0X3180, 0XF141, 0X3300, 0XF3C1,
0XF281, 0X3240, 0X3600, 0XF6C1, 0XF781, 0X3740, 0XF501, 0X35C0, 0X3480, 0XF441,
0X3C00, 0XFCC1, 0XFD81, 0X3D40, 0XFF01, 0X3FC0, 0X3E80, 0XFE41, 0XFA01, 0X3AC0,
0X3B80, 0XFB41, 0X3900, 0XF9C1, 0XF881, 0X3840, 0X2800, 0XE8C1, 0XE981, 0X2940,
0XEB01, 0X2BC0, 0X2A80, 0XEA41, 0XEE01, 0X2EC0, 0X2F80, 0XEF41, 0X2D00, 0XEDC1,
0XEC81, 0X2C40, 0XE401, 0X24C0, 0X2580, 0XE541, 0X2700, 0XE7C1, 0XE681, 0X2640,
0X2200, 0XE2C1, 0XE381, 0X2340, 0XE101, 0X21C0, 0X2080, 0XE041, 0XA001, 0X60C0,
0X6180, 0XA141, 0X6300, 0XA3C1, 0XA281, 0X6240, 0X6600, 0XA6C1, 0XA781, 0X6740,
0XA501, 0X65C0, 0X6480, 0XA441, 0X6C00, 0XACC1, 0XAD81, 0X6D40, 0XAF01, 0X6FC0,
0X6E80, 0XAE41, 0XAA01, 0X6AC0, 0X6B80, 0XAB41, 0X6900, 0XA9C1, 0XA881, 0X6840,
0X7800, 0XB8C1, 0XB981, 0X7940, 0XBB01, 0X7BC0, 0X7A80, 0XBA41, 0XBE01, 0X7EC0,
0X7F80, 0XBF41, 0X7D00, 0XBDC1, 0XBC81, 0X7C40, 0XB401, 0X74C0, 0X7580, 0XB541,
0X7700, 0XB7C1, 0XB681, 0X7640, 0X7200, 0XB2C1, 0XB381, 0X7340, 0XB101, 0X71C0,
0X7080, 0XB041, 0X5000, 0X90C1, 0X9181, 0X5140, 0X9301, 0X53C0, 0X5280, 0X9241,
0X9601, 0X56C0, 0X5780, 0X9741, 0X5500, 0X95C1, 0X9481, 0X5440, 0X9C01, 0X5CC0,
0X5D80, 0X9D41, 0X5F00, 0X9FC1, 0X9E81, 0X5E40, 0X5A00, 0X9AC1, 0X9B81, 0X5B40,
0X9901, 0X59C0, 0X5880, 0X9841, 0X8801, 0X48C0, 0X4980, 0X8941, 0X4B00, 0X8BC1,
0X8A81, 0X4A40, 0X4E00, 0X8EC1, 0X8F81, 0X4F40, 0X8D01, 0X4DC0, 0X4C80, 0X8C41,
0X4400, 0X84C1, 0X8581, 0X4540, 0X8701, 0X47C0, 0X4680, 0X8641, 0X8201, 0X42C0,
0X4380, 0X8341, 0X4100, 0X81C1, 0X8081, 0X4040
};
//==========================================================================//
//
//==========================================================================//
public static int GetCrc_Fast(byte[] buf, int len)
{
int icrc = 0xFFFF;
for(int i = 0; i < len; i++)
{
icrc = (icrc >> 8 ) ^ CRCTable[(icrc ^ buf[i]) & 0xff];
}
return icrc;
}
// Compute the MODBUS RTU CRC, version 1.
public static int GetCRC(byte[] buf, int len)
{
UInt16 crc = 0xFFFF;
for (int pos = 0; pos < len; pos++) {
crc ^= (UInt16)buf[pos]; // XOR byte into least sig. byte of crc
for (int i = 8; i != 0; i--) { // Loop over each bit
if ((crc & 0x0001) != 0) { // If the LSB is set
crc >>= 1; // Shift right and XOR 0xA001
crc ^= 0xA001;
}
else // Else LSB is not set
crc >>= 1; // Just shift right
}
}
//byte[] crc_bytes = BitConverter.GetBytes(crc);
return crc;
}
}
Here’s the PowerShell section
function Get-CRCModRTU {
<#
.SYNOPSIS
Calculate CRC using the C# ModRTY implementation
.DESCRIPTION
Calculate CRC using the C# ModRTY implementation
.EXAMPLE
Get-CRCModRTUFast $data
.INPUTS
byte[]
.OUTPUTS
uint32
#>
[CmdletBinding(SupportsShouldProcess)]
param (
# Array of Bytes to use for CRC calculation
[Parameter(Mandatory=$true, Position = 0)]
[ValidateNotNullOrEmpty()]
[byte[]]$Bytes
)
Begin {
if (!("ModRTU_CRC" -as [type])) {
Write-Verbose "Registering ModRTU_CRC... "
try{
Add-Type "$Script:CsSource"
}catch{}
}
}
process{
try{
Write-Verbose "[Get-CRCModRTU] clone data"
[byte[]]$dataArray = $Bytes.Clone()
[uint32]$inputLength = $dataArray.Length
Write-Verbose "[Get-CRCModRTU] GetCrc (len $inputLength bytes)"
[uint32]$crc_value = [ModRTU_CRC]::GetCRC($dataArray, $inputLength)
Write-output $crc_value
}catch{
Write-Error "$_"
}
}
}
function Get-CRCModRTUFast {
<#
.SYNOPSIS
Calculate CRC using the C# ModRTY implementation
.DESCRIPTION
Calculate CRC using the C# ModRTY implementation (fast)
.EXAMPLE
Get-CRCModRTUFast $data
.INPUTS
byte[]
.OUTPUTS
uint32
#>
[CmdletBinding(SupportsShouldProcess)]
param (
# Array of Bytes to use for CRC calculation
[Parameter(Mandatory=$true, Position = 0)]
[ValidateNotNullOrEmpty()]
[byte[]]$Bytes
)
Begin {
if (!("ModRTU_CRC" -as [type])) {
Write-Verbose "Registering ModRTU_CRC... "
try{
Add-Type "$Script:CsSource"
}catch{}
}
}
process{
try{
Write-Verbose "[Get-CRCModRTUFast] clone data"
[byte[]]$dataArray = $Bytes.Clone()
[uint32]$inputLength = $dataArray.Length
Write-Verbose "[Get-CRCModRTUFast] GetCrc_Fast (len $inputLength bytes)"
[uint32]$crc_value = [ModRTU_CRC]::GetCrc_Fast($dataArray, $inputLength)
Write-output $crc_value
}catch{
Write-Error "$_"
}
}
}
Wrapper Function
this function gets a file name and retrieves the bytes to process in other CRC functions
function Get-FileCRC32 {
<#
.SYNOPSIS
Calculate CRC of a file.
.DESCRIPTION
This function calculates the CRC of the input file using the CRC32 algorithm.
.EXAMPLE
Get-FileCRC32 $path
.INPUTS
string
.OUTPUTS
uint32
#>
[CmdletBinding(SupportsShouldProcess)]
param (
# Array of Bytes to use for CRC calculation
[Parameter(Mandatory=$true, Position = 0)]
[ValidateScript({
if(-Not ($_ | Test-Path) ){
throw "File or folder does not exist"
}
if(-Not ($_ | Test-Path -PathType Leaf) ){
throw "The Destination Path argument must be a file. Directory paths are not allowed."
}
return $true
})]
[string]$Path,
[ValidateSet('Block32','ModRTU','ModRTUFast')]
[string]$Algorithm='Block32'
)
begin{
Write-Verbose "[Get-FileCRC32] ReadAllBytes start (`"$Path`")"
# Portable Get-Content to bytes, the .NET is faster a bit
[byte[]] $file_bytes = [System.IO.File]::ReadAllBytes("$Path")
Write-Verbose "[Get-FileCRC32] ReadAllBytes done ($($file_bytes.Length) bytes)"
}
process{
try{
[uint32]$crc = 0
switch($Algorithm){
'Block32' { [uint32]$crc = Get-CRC32 $file_bytes }
'ModRTU' { [uint32]$crc = Get-CRCModRTU $file_bytes }
'ModRTUFast' { [uint32]$crc = Get-CRCModRTUFast $file_bytes }
default { [uint32]$crc = Get-CRC32 $file_bytes }
}
return $crc
}catch{
write-error "$_"
}
}
}
Performance Test Results
Get the code
Crc32 on PowerShell.Public.Sandbox GitHub
Crc32 on PowerShell.Reddit.Support GitHub
Important Note Do You have Issues accessing the core repository? Don’t be shy and send me an EMAIL to guillaumeplante.qc@gmail.com and I will fix access for you
