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.TH VDELTA 3 "16 July 1994"

.SH NAME

vdelta \- data differencing and compression

.SH SYNOPSIS

.MW "#include <vdelta.h>"

.nf

.MW "long vddelta(Vddisc_t* source, Vddisc_t* target, Vddisc_t* delta);"

.MW "long vdupdate(Vddisc_t* source, Vddisc_t* target, Vddisc_t* delta);"

.MW "int vdsqueeze(Void_t* target, int n, Void_t* delta);"

.MW "int vdexpand(Void_t* target, int n, Void_t* delta);"

.fi

.SH DESCRIPTION

These functions embody an algorithm for determining a compressed form of the

difference between two byte streams,

and for applying that difference to a byte stream.

.PP

.I Vddelta

computes a transformation (encoded as the byte stream \f5delta\fP)

that maps the source byte stream \f5source\fP

to the target byte stream \f5target\fP.

If the source stream is empty (\f5source\fP is \f5NULL\fP or

\f5source->size\fP is non-positive),

\fIvddelta\fP acts like a compression routine.

\fIVddelta\fP returns the length of the transformation byte stream.

.PP

.I Vdupdate

applies a transformation \f5delta\fP generated by

\fIvddelta\fP to the source byte stream \f5source\fP

and emits the target byte stream \f5target\fP.

\fIVdupdate\fP returns the length of the target byte stream.

.PP

.I Vdsqueeze

compresses the string \f5target\fP of length \f5n\fP and outputs

the compressed data to the string \f5delta\fP.

\fIVdsqueeze\fP returns the length of the compressed data.

.PP

.I Vdexpand

decompresses compressed data in \f5delta\fP into the \f5target\fP area

which is of size \f5n\fP.

\fIVdexpand\fP returns the length of the decompressed data.

.PP

The handling of data for a data stream is defined

by a discipline structure of type \f5Vddisc_t\fP.

This type contains the following members:

.in +.5i

.nf

.MW "long size;"

.MW "Void_t* data;"

.MW "int (*readf)(Void_t* buf, int n, long offset, Vddisc_t* disc);"

.MW "int (*writef)Void_t* buf, int n, long offset, Vddisc_t* disc);"

.fi

.in -.5i

.TP

\f5size\fP defines the length of the respective data stream.

.TP

\f5data\fP, if not \f5NULL\fP, is an array that either contains

the entire data for a read stream or is large enough to store

the entire generated data. For example, in the \fIvddelta\fP call,

\f5target->size\fP defines the length of the target stream.

In this case, if \f5target->data\fP is not \f5NULL\fP,

it is assumed to contain all of the target data

(therefore, \f5target->readf\fP is not required.)

.TP

.MW readf

points to a function that reads at most \f5n\fP bytes

into \f5buf\fP from position \f5offset\fP

in the byte stream specified by the as described above, and

returns the number of bytes actually read, or \-1 on error.

The argument \f5disc\fP is the containing discipline structure.

.TP

.MW writef

is identical to \f5readf\fP except that it writes rather than reads bytes.

.TP

.PP

\f5Void_t\fP is \f5#define\fPd as \f5void\fP if possible, otherwise \f5char\fP.

.SH DIAGNOSTICS

\fIVddelta\fP, \fIvdupdate\fP, \fIvdsqueeze\fP and \fIvdexpand\fP

return \-1 on error.

.SH AUTHORS

Kiem-Phong Vo, kpv@research.att.com, AT&T Bell Laboratories

.br

David G. Korn, dgk@research.att.com, AT&T Bell Laboratories