ref: 905e669fced93d8f1648157ade1456227230b979
dir: /man/2/rabin/
.TH RABIN 2
.SH NAME
rabin \- rabin fingerprinting
.SH SYNOPSIS
.EX
include "rabin.m";
rabin := load Rabin Rabin->PATH;
Rcfg, Rfile: import rabin;
init: fn(bufio: Bufio);
open: fn(rcfg: ref Rcfg, b: ref Iobuf, min, max: int): (ref Rfile, string);
Rcfg: adt {
mk: fn(prime, width, mod: int): (ref Rcfg, string);
};
Rfile: adt {
read: fn(r: self ref Rfile): (array of byte, big, string);
};
.EE
.SH DESCRIPTION
.B Rabin
implements a data fingerprinting algorithm. A rolling checksum is calculated while reading data. Certain checksum values are taken to be data boundaries and used to split the data into chunks.
.PP
.B Rcfg
represents the parameters to the algorithm;
.B Rcfg.mk
creates a new instance.
.I Prime
should be a prime number.
.I Width
is the width of the rolling checksum window in bytes. A wider window results in more diverse boundary patterns. A window of 30 bytes should be reasonable for most uses.
.I Mod
effectively sets the mean desired chunk size. The rolling checksum is calculated modulo
.IR mod .
All three parameters influence where chunk boundaries will be found.
.PP
.B Rfile
represents a file to read chunks from.
.B Open
returns an initialised Rfile or an error string.
.I Min
and
.I max
are the minimum and maximum size in bytes of chunks that will be returned. Only the last chunk in a file can be smaller than the minimum chunk size. Note that the mean chunk size may be off due to these parameters.
Data is read from
.B Iobuf
.IR b .
.B Rfile.read
returns subsequent chunks of data and the file offset at which they were found, or an error message. After end of file, the returned chunks are zero bytes long.
.SH SOURCE
.B /appl/lib/rabin.b
.SH AUTHOR
Mechiel Lukkien, during GSoC 2007