Click here to Skip to main content
15,173,646 members
Articles / Programming Languages / C#
Posted 29 Oct 2007


25 bookmarked

Adler-32 Checksum Calculation

Rate me:
Please Sign up or sign in to vote.
3.22/5 (8 votes)
29 Oct 2007CPOL2 min read
Presents a C# implementation of Adler-32 checksum calculation for use in the .NET Framework


Checksums are a common way to ensure data integrity. Adler-32 checksum may be used for revealing the damaged files or to compare two files for identity.

Background (from

Adler-32 is a checksum algorithm which was invented by Mark Adler. It is almost as reliable as a 32-bit cyclic redundancy check for protecting against accidental modification of data, such as distortions occurring during a transmission.

An Adler-32 checksum is obtained by calculating two 16-bit checksums A and B and concatenating their bits into a 32-bit integer. A is the sum of all bytes in the string; B is the sum of the individual values of A from each step. At the beginning of an Adler-32 run, A is initialized to 1, B to 0. The sums are done modulo 65521 (the largest prime number smaller than 216). The bytes are stored in network order (big endian), B occupying the two most significant bytes. The function may be expressed as A = 1 + D1 + D2 + ... + DN (mod 65521) B = (1 + D1) + (1 + D1 + D2) + ... + (1 + D1 + D2 + ... + DN) (mod 65521) = N×D1 + (N-1)×D2 + (N-2)×D3 + ... + DN + N (mod 65521) Adler-32(D) = B * 65536 + A where D is the string of bytes for which the checksum is to be calculated, and N is the length of D.

Using the Code

Here are the steps needed to add Adler-32 checksum into your program without worrying about how it works:

  • Add the source code AdlerChecksum.cs to your project and add to your source file using FileHelper;
  • Create an instance of the AdlerChecksum class.
  • Call MakeForFile method for checksum calculation.
  • Get Adler-32 checksum value by ChecksumValue property. For printing method ToString can be used.

See example code below:

// Adler-32 checksum using
 AdlerChecksum acs = new AdlerChecksum();
 if (acs.MakeForFile(textPath.Text))
    textVal.Text = acs.ToString(); //success
    textVal.Text = "Unable to get checksum!"; //failure


I hope this code will be useful! Thanks all for the comments and critique. New suggestions and ideas are welcome.


  • Version, 29th October 2007 - First initial release


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Software Developer (Senior) Elmo Motion Control
Israel Israel
Software developer since 1992

Comments and Discussions

Questionwhat type of hashing is used in it Pin
zameer990915-Apr-10 14:00
Memberzameer990915-Apr-10 14:00 
GeneralAccuracy Pin
seandillon12-Nov-07 2:47
Memberseandillon12-Nov-07 2:47 
GeneralApalling. Pin
GZero5-Nov-07 2:01
MemberGZero5-Nov-07 2:01 
GeneralRe: Apalling. Pin
merlin9817-Nov-07 5:37
professionalmerlin9817-Nov-07 5:37 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Praise Praise    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.