scc::encode::Adler32 Class Reference

Adler-32 checksum allowing rolling calculation. More...

#include <adler32.h>

Public Member Functions
	Adler32 ()
	Construct with initialized value.
	Adler32 (const void *loc, int len)
	Construct with initial value. More...
	operator uint32_t () const
uint32_t	val () const
int	size ()
	Size of the current window.
uint32_t	reset ()
	Reset the checksum.
uint32_t	reset (const void *loc, int len)
	Reset the checksum, and update with initial value. More...
uint32_t	update (const void *, int)
	Update the checksum with buffer contents. More...
uint32_t	combine (const Adler32 &)
uint32_t	rotate (unsigned char, unsigned char)
	Update the checksum with next byte. More...
uint32_t	rotate (char xrem, char xadd)

Detailed Description

Adler-32 checksum allowing rolling calculation.

Rolling calculation allows very fast calculations within a sliding window, removing the overhead of recalculating for the entire window size.

Test example from scclib/encode/unittest/adler32.cc

static string test =
"ljpoaweu9uwat7a9g0ujaW219U0U;DSJGEOPUJGAfPVAPUAS:FGJALGJ7804-85,"      // 64 bytes
"G;AKGPTG[ASIGSFDAS[DFSAPDFJASPFJSPADFJPAJPGAJSGSAGJAPJGAPJGPOIOO";     // 64 bytes
static uint32_t all_ad = 0xf9932612;        // all bytes
static uint32_t last64_ad = 0x583e1280;     // last 64 bytes

    Adler32 ad;
    size_t sz = test.size();                // 128 bytes
    
    ad.reset(test.data(), sz/2);            // first 64 bytes, sets window size to 64
    ASSERT_EQ(ad.size(), 64);
    
    // rolling 64 byte window, will calculate the checksum at each 64 byte window
    for (size_t i = 0; i < 64; i++)
    {
        ad.rotate(test[i], test[64+i]);     // first byte is 0-63, last is 64-127
    }
    ASSERT_EQ(ad, last64_ad);               // end up with the last 64 bytes checksum

Examples

scclib/encode/unittest/adler32.cc.

Definition at line 32 of file adler32.h.

Constructor & Destructor Documentation

Adler32()

scc::encode::Adler32::Adler32 ( const void *  loc, int  len  )

inline

Construct with initial value.

Parameters

loc	Buffer location.
len	Buffer size.

Definition at line 43 of file adler32.h.

Member Function Documentation

reset()

uint32_t scc::encode::Adler32::reset ( const void *  loc, int  len  )

inline

Reset the checksum, and update with initial value.

Parameters

loc	Buffer location.
len	Buffer size. Window length is set to len.

Definition at line 72 of file adler32.h.

rotate()

uint32_t Adler32::rotate	(	unsigned char	xrem,
		unsigned char	xadd
	)

Update the checksum with next byte.

Usable for a "rolling window" checksum.

For example for bytes 01234 with checksum ch1, calling rotate('0', '5') will produce a checksum ad2 on bytes 12345.

Parameters

xrem	Byte to rotate out (first in old window)
xadd	Byte to rotate in (last in new window)

see https://openresearch-repository.anu.edu.au/bitstream/1885/40765/3/TR-CS-96-05.pdf

Definition at line 36 of file adler32.cc.

update()

uint32_t Adler32::update	(	const void *	loc,
		int	len
	)

Update the checksum with buffer contents.

Parameters

loc	Buffer location.
len	Buffer size. Window length is increased by len.

Definition at line 7 of file adler32.cc.

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The documentation for this class was generated from the following files:

• encode/pub/encode/adler32.h
• encode/adler32.cc