sargon.lz77

Components that can compress and expand ranges.

Description:
Compression is useful for storage and transmission data formats. This compresses using a variant of the LZ77 compression algorithm. compress() and expand() are meant to be a matched set. Users should not depend on the particular data format.

Example:
This program takes a filename as an argument, compresses it, expands it, and verifies that the result matches the original contents.

int main(string args[])
{
    import std.stdio;
    import std.algorithm;
    import std.file;
    import std.compression.lz77;

    string filename;
    if (args.length < 2)
    {
        printf("need filename argument\n");
        return 1;
    }
    else
        filename = args[1];

    ubyte[] si = cast(ubyte[])std.file.read(filename);

    // Compress
    auto di = new ubyte[maxCompressedSize(si.length)];
    auto result = si.compress().copy(di);

    di = di[0..$ - result.length];

    writefln("Compression done, srclen = %s compressed = %s",
        si.length, di.length);

    // Decompress
    ubyte[] si2 = new ubyte[si.length];
    result = di.expand().copy(si2);
    assert(result.length == 0);

    writefln("Decompression done, dilen = %s decompressed = %s",
        di.length, si2.length);

    if (si != si2)
    {
        writeln("Buffers don't match");
        assert(0);
    }

    return 0;
}

References:
Wikipedia

License:
Boost License 1.0.

Authors:
Walter Bright

Source:
src/sargon/lz77.d

size_t maxCompressedSize(size_t length);

Compute the max size of a buffer needed to hold the compressed result.

Parameters:
length number of bytes of uncompressed data

Returns:
max size of compressed buffer

class CompressException: object.Exception;

Exception thrown on errors in compression functions, likely caused by corrupted data.

auto compress(R)(R src) if (isInputRange!R && is(ElementType!R : ubyte));

Component that returns a Range that will compress src using LZ77 compression.

Description:
Compresses input of arbitrarily large size.

compress() does not allocate memory, although it uses a little over 8Kb of stack if src is not an array.

Parameters:
src An InputRange of ubytes. If it is an array, it will go faster and will use much less stack.

Returns:
InputRange

auto expand(R)(R src) if (isInputRange!R && is(ElementType!R : ubyte));

Component to expand compressed result of LZ77 Compress.

Description:
Does not allocate memory. The expand operation is quite a bit faster than the corresponding compress.

Parameters:
src An InputRange over data generated by compress.

Returns:
An InputRange which provides the expanded data.