# ICSharpCode.SharpZipLib.Checksum.Adler32 - Coverage Report

# Summary

Class: | ICSharpCode.SharpZipLib.Checksum.Adler32
Assembly: | ICSharpCode.SharpZipLib
File(s): | C:\Users\Neil\Documents\Visual Studio 2015\Projects\icsharpcode\SZL_master\ICSharpCode.SharpZipLib\Checksum\Adler32.cs
Covered lines: | 35
Uncovered lines: | 6
Coverable lines: | 41
Total lines: | 175
Line coverage: | 85.3%
Branch coverage: | 100%

# Metrics

Method | Cyclomatic Complexity | Sequence Coverage | Branch Coverage
--- | --- | --- | ---
.ctor() | 1 | 100 | 100
Reset() | 1 | 100 | 100
Update(...) | 1 | 0 | 0
Update(...) | 2 | 100 | 100
Update(...) | 9 | 100 | 100
.cctor() | 1 | 100 | 100

# File(s)

## C:\Users\Neil\Documents\Visual Studio 2015\Projects\icsharpcode\SZL_master\ICSharpCode.SharpZipLib\Checksum\Adler32.cs

| # | Line |  | Line coverage
--- | --- | --- | --- | ---
|  | `1` |  | `using System;`
|  | `2` |  | ``
|  | `3` |  | `namespace ICSharpCode.SharpZipLib.Checksum`
|  | `4` |  | `{`
|  | `5` |  | `/// <summary>`
|  | `6` |  | `/// Computes Adler32 checksum for a stream of data. An Adler32`
|  | `7` |  | `/// checksum is not as reliable as a CRC32 checksum, but a lot faster to`
|  | `8` |  | `/// compute.`
|  | `9` |  | `///`
|  | `10` |  | `/// The specification for Adler32 may be found in RFC 1950.`
|  | `11` |  | `/// ZLIB Compressed Data Format Specification version 3.3)`
|  | `12` |  | `///`
|  | `13` |  | `///`
|  | `14` |  | `/// From that document:`
|  | `15` |  | `///`
|  | `16` |  | `/// "ADLER32 (Adler-32 checksum)`
|  | `17` |  | `/// This contains a checksum value of the uncompressed data`
|  | `18` |  | `/// (excluding any dictionary data) computed according to Adler-32`
|  | `19` |  | `/// algorithm. This algorithm is a 32-bit extension and improvement`
|  | `20` |  | `/// of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073`
|  | `21` |  | `/// standard.`
|  | `22` |  | `///`
|  | `23` |  | `/// Adler-32 is composed of two sums accumulated per byte: s1 is`
|  | `24` |  | `/// the sum of all bytes, s2 is the sum of all s1 values. Both sums`
|  | `25` |  | `/// are done modulo 65521. s1 is initialized to 1, s2 to zero. The`
|  | `26` |  | `/// Adler-32 checksum is stored as s2*65536 + s1 in most-`
|  | `27` |  | `/// significant-byte first (network) order."`
|  | `28` |  | `///`
|  | `29` |  | `/// "8.2. The Adler-32 algorithm`
|  | `30` |  | `///`
|  | `31` |  | `/// The Adler-32 algorithm is much faster than the CRC32 algorithm yet`
|  | `32` |  | `/// still provides an extremely low probability of undetected errors.`
|  | `33` |  | `///`
|  | `34` |  | `/// The modulo on unsigned long accumulators can be delayed for 5552`
|  | `35` |  | `/// bytes, so the modulo operation time is negligible. If the bytes`
|  | `36` |  | `/// are a, b, c, the second sum is 3a + 2b + c + 3, and so is position`
|  | `37` |  | `/// and order sensitive, unlike the first sum, which is just a`
|  | `38` |  | `/// checksum. That 65521 is prime is important to avoid a possible`
|  | `39` |  | `/// large class of two-byte errors that leave the check unchanged.`
|  | `40` |  | `/// (The Fletcher checksum uses 255, which is not prime and which also`
|  | `41` |  | `/// makes the Fletcher check insensitive to single byte changes 0 -`
|  | `42` |  | `/// 255.)`
|  | `43` |  | `///`
|  | `44` |  | `/// The sum s1 is initialized to 1 instead of zero to make the length`
|  | `45` |  | `/// of the sequence part of s2, so that the length does not have to be`
|  | `46` |  | `/// checked separately. (Any sequence of zeroes has a Fletcher`
|  | `47` |  | `/// checksum of zero.)"`
|  | `48` |  | `/// </summary>`
|  | `49` |  | `/// <see cref="ICSharpCode.SharpZipLib.Zip.Compression.Streams.InflaterInputStream"/>`
|  | `50` |  | `/// <see cref="ICSharpCode.SharpZipLib.Zip.Compression.Streams.DeflaterOutputStream"/>`
|  | `51` |  | `public sealed class Adler32 : IChecksum`
|  | `52` |  | `{`
|  | `53` |  | `#region Instance Fields`
|  | `54` |  | `/// <summary>`
|  | `55` |  | `/// largest prime smaller than 65536`
|  | `56` |  | `/// </summary>`
| 1 | `57` |  | `readonly static uint BASE = 65521;`
|  | `58` |  | ``
|  | `59` |  | `/// <summary>`
|  | `60` |  | `/// The CRC data checksum so far.`
|  | `61` |  | `/// </summary>`
|  | `62` |  | `uint checkValue;`
|  | `63` |  | `#endregion`
|  | `64` |  | ``
|  | `65` |  | `/// <summary>`
|  | `66` |  | `/// Initialise a default instance of <see cref="Adler32"></see>`
|  | `67` |  | `/// </summary>`
| 709 | `68` |  | `public Adler32()`
|  | `69` |  | `{`
| 709 | `70` |  | `Reset();`
| 709 | `71` |  | `}`
|  | `72` |  | ``
|  | `73` |  | `/// <summary>`
|  | `74` |  | `/// Resets the Adler32 data checksum as if no update was ever called.`
|  | `75` |  | `/// </summary>`
|  | `76` |  | `public void Reset()`
|  | `77` |  | `{`
| 1143 | `78` |  | `checkValue = 1;`
| 1143 | `79` |  | `}`
|  | `80` |  | ``
|  | `81` |  | `/// <summary>`
|  | `82` |  | `/// Returns the Adler32 data checksum computed so far.`
|  | `83` |  | `/// </summary>`
|  | `84` |  | `public long Value {`
|  | `85` |  | `get {`
| 18 | `86` |  | `return checkValue;`
|  | `87` |  | `}`
|  | `88` |  | `}`
|  | `89` |  | ``
|  | `90` |  | `/// <summary>`
|  | `91` |  | `/// Updates the checksum with the byte b.`
|  | `92` |  | `/// </summary>`
|  | `93` |  | `/// <param name="bval">`
|  | `94` |  | `/// The data value to add. The high byte of the int is ignored.`
|  | `95` |  | `/// </param>`
|  | `96` |  | `public void Update(int bval)`
|  | `97` |  | `{`
|  | `98` |  | `// We could make a length 1 byte array and call update again, but I`
|  | `99` |  | `// would rather not have that overhead`
| 0 | `100` |  | `uint s1 = checkValue & 0xFFFF;`
| 0 | `101` |  | `uint s2 = checkValue >> 16;`
|  | `102` |  | ``
| 0 | `103` |  | `s1 = (s1 + ((uint)bval & 0xFF)) % BASE;`
| 0 | `104` |  | `s2 = (s1 + s2) % BASE;`
|  | `105` |  | ``
| 0 | `106` |  | `checkValue = (s2 << 16) + s1;`
| 0 | `107` |  | `}`
|  | `108` |  | ``
|  | `109` |  | `/// <summary>`
|  | `110` |  | `/// Updates the Adler32 data checksum with the bytes taken from`
|  | `111` |  | `/// a block of data.`
|  | `112` |  | `/// </summary>`
|  | `113` |  | `/// <param name="buffer">Contains the data to update the checksum with.</param>`
|  | `114` |  | `public void Update(byte[] buffer)`
|  | `115` |  | `{`
| 2 | `116` |  | `if (buffer == null) {`
| 1 | `117` |  | `throw new ArgumentNullException(nameof(buffer));`
|  | `118` |  | `}`
|  | `119` |  | ``
| 1 | `120` |  | `Update(buffer, 0, buffer.Length);`
| 1 | `121` |  | `}`
|  | `122` |  | ``
|  | `123` |  | `/// <summary>`
|  | `124` |  | `/// Update Adler32 data checksum based on a portion of a block of data`
|  | `125` |  | `/// </summary>`
|  | `126` |  | `/// <param name = "buffer">Contains the data to update the CRC with.</param>`
|  | `127` |  | `/// <param name = "offset">The offset into the buffer where the data starts</param>`
|  | `128` |  | `/// <param name = "count">The number of data bytes to update the CRC with.</param>`
|  | `129` |  | `public void Update(byte[] buffer, int offset, int count)`
|  | `130` |  | `{`
| 6204 | `131` |  | `if (buffer == null) {`
| 1 | `132` |  | `throw new ArgumentNullException(nameof(buffer));`
|  | `133` |  | `}`
|  | `134` |  | ``
| 6203 | `135` |  | `if (offset < 0) {`
| 1 | `136` |  | `throw new ArgumentOutOfRangeException(nameof(offset), "cannot be less than zero");`
|  | `137` |  | `}`
|  | `138` |  | ``
| 6202 | `139` |  | `if (offset >= buffer.Length) {`
| 1 | `140` |  | `throw new ArgumentOutOfRangeException(nameof(offset), "not a valid index into buffer");`
|  | `141` |  | `}`
|  | `142` |  | ``
| 6201 | `143` |  | `if (count < 0) {`
| 1 | `144` |  | `throw new ArgumentOutOfRangeException(nameof(count), "cannot be less than zero");`
|  | `145` |  | `}`
|  | `146` |  | ``
| 6200 | `147` |  | `if (offset + count > buffer.Length) {`
| 1 | `148` |  | `throw new ArgumentOutOfRangeException(nameof(count), "exceeds buffer size");`
|  | `149` |  | `}`
|  | `150` |  | ``
|  | `151` |  | `//(By Per Bothner)`
| 6199 | `152` |  | `uint s1 = checkValue & 0xFFFF;`
| 6199 | `153` |  | `uint s2 = checkValue >> 16;`
|  | `154` |  | ``
| 13890 | `155` |  | `while (count > 0) {`
|  | `156` |  | `// We can defer the modulo operation:`
|  | `157` |  | `// s1 maximally grows from 65521 to 65521 + 255 * 3800`
|  | `158` |  | `// s2 maximally grows by 3800 * median(s1) = 2090079800 < 2^31`
| 7691 | `159` |  | `int n = 3800;`
| 7691 | `160` |  | `if (n > count) {`
| 6199 | `161` |  | `n = count;`
|  | `162` |  | `}`
| 7691 | `163` |  | `count -= n;`
| 8355525 | `164` |  | `while (--n >= 0) {`
| 8347834 | `165` |  | `s1 = s1 + (uint)(buffer[offset++] & 0xff);`
| 8347834 | `166` |  | `s2 = s2 + s1;`
|  | `167` |  | `}`
| 7691 | `168` |  | `s1 %= BASE;`
| 7691 | `169` |  | `s2 %= BASE;`
|  | `170` |  | `}`
|  | `171` |  | ``
| 6199 | `172` |  | `checkValue = (s2 << 16) | s1;`
| 6199 | `173` |  | `}`
|  | `174` |  | `}`
|  | `175` |  | `}`