Inheritance diagram for ICSharpCode::SharpZipLib::Checksums::Adler32:
Public Member Functions | |
Adler32 () | |
Creates a new instance of the Adler32 class. The checksum starts off with a value of 1. | |
void | Reset () |
Resets the Adler32 checksum to the initial value. | |
void | Update (int bval) |
Updates the checksum with the byte b. | |
void | Update (byte[] buffer) |
Updates the checksum with an array of bytes. | |
void | Update (byte[] buf, int off, int len) |
Updates the checksum with the bytes taken from the array. | |
Properties | |
long | Value |
Returns the Adler32 data checksum computed so far. | |
Private Attributes | |
uint | checksum |
Static Private Attributes | |
static readonly uint | BASE = 65521 |
largest prime smaller than 65536 |
The specification for Adler32 may be found in RFC 1950. ZLIB Compressed Data Format Specification version 3.3)
From that document:
"ADLER32 (Adler-32 checksum) This contains a checksum value of the uncompressed data (excluding any dictionary data) computed according to Adler-32 algorithm. This algorithm is a 32-bit extension and improvement of the Fletcher algorithm, used in the ITU-T X.224 / ISO 8073 standard.
Adler-32 is composed of two sums accumulated per byte: s1 is the sum of all bytes, s2 is the sum of all s1 values. Both sums are done modulo 65521. s1 is initialized to 1, s2 to zero. The Adler-32 checksum is stored as s2*65536 + s1 in most- significant-byte first (network) order."
"8.2. The Adler-32 algorithm
The Adler-32 algorithm is much faster than the CRC32 algorithm yet still provides an extremely low probability of undetected errors.
The modulo on unsigned long accumulators can be delayed for 5552 bytes, so the modulo operation time is negligible. If the bytes are a, b, c, the second sum is 3a + 2b + c + 3, and so is position and order sensitive, unlike the first sum, which is just a checksum. That 65521 is prime is important to avoid a possible large class of two-byte errors that leave the check unchanged. (The Fletcher checksum uses 255, which is not prime and which also makes the Fletcher check insensitive to single byte changes 0 - 255.)
The sum s1 is initialized to 1 instead of zero to make the length of the sequence part of s2, so that the length does not have to be checked separately. (Any sequence of zeroes has a Fletcher checksum of zero.)"
ICSharpCode::SharpZipLib::Zip::Compression::Streams::InflaterInputStream ICSharpCode::SharpZipLib::Zip::Compression::Streams::DeflaterOutputStream
Definition at line 89 of file Adler32.cs.
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Creates a new instance of the Adler32 class. The checksum starts off with a value of 1.
Definition at line 111 of file Adler32.cs. |
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Resets the Adler32 checksum to the initial value.
Implements ICSharpCode::SharpZipLib::Checksums::IChecksum. Definition at line 119 of file Adler32.cs. |
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Updates the checksum with the bytes taken from the array.
Implements ICSharpCode::SharpZipLib::Checksums::IChecksum. Definition at line 166 of file Adler32.cs. |
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Updates the checksum with an array of bytes.
Implements ICSharpCode::SharpZipLib::Checksums::IChecksum. Definition at line 149 of file Adler32.cs. |
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Updates the checksum with the byte b.
Implements ICSharpCode::SharpZipLib::Checksums::IChecksum. Definition at line 130 of file Adler32.cs. |
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largest prime smaller than 65536
Definition at line 94 of file Adler32.cs. |
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Definition at line 96 of file Adler32.cs. |
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Returns the Adler32 data checksum computed so far.
Implements ICSharpCode::SharpZipLib::Checksums::IChecksum. Definition at line 101 of file Adler32.cs. |