Method: Zstdlib::Deflate#initialize

Defined in:
ext/zstdlib/ruby/zlib-2.6/zstdlib.c,
ext/zstdlib/ruby/zlib-2.5/zstdlib.c,
ext/zstdlib/ruby/zlib-2.4/zstdlib.c,
ext/zstdlib/ruby/zlib-2.3/zstdlib.c,
ext/zstdlib/ruby/zlib-2.2/zstdlib.c

#initialize(*args) ⇒ Object

call-seq: Zstdlib::Deflate.new(level=DEFAULT_COMPRESSION, window_bits=MAX_WBITS, mem_level=DEF_MEM_LEVEL, strategy=DEFAULT_STRATEGY)

Creates a new deflate stream for compression. If a given argument is nil, the default value of that argument is used.

The +level+ sets the compression level for the deflate stream between 0 (no compression) and 9 (best compression). The following constants have been defined to make code more readable:

  • Zstdlib::DEFAULT_COMPRESSION
  • Zstdlib::NO_COMPRESSION
  • Zstdlib::BEST_SPEED
  • Zstdlib::BEST_COMPRESSION

See http://www.zlib.net/manual.html#Constants for further information.

The +window_bits+ sets the size of the history buffer and should be between 8 and 15. Larger values of this parameter result in better compression at the expense of memory usage.

The +mem_level+ specifies how much memory should be allocated for the internal compression state. 1 uses minimum memory but is slow and reduces compression ratio while 9 uses maximum memory for optimal speed. The default value is 8. Two constants are defined:

  • Zstdlib::DEF_MEM_LEVEL
  • Zstdlib::MAX_MEM_LEVEL

The +strategy+ sets the deflate compression strategy. The following strategies are available:

Zstdlib::DEFAULT_STRATEGY:: For normal data Zstdlib::FILTERED:: For data produced by a filter or predictor Zstdlib::FIXED:: Prevents dynamic Huffman codes Zstdlib::HUFFMAN_ONLY:: Prevents string matching Zstdlib::RLE:: Designed for better compression of PNG image data

See the constants for further description.

== Examples

=== Basic

open "compressed.file", "w+" do |io| io << Zstdlib::Deflate.new.deflate(File.read("big.file")) end

=== Custom compression

open "compressed.file", "w+" do |compressed_io| deflate = Zstdlib::Deflate.new(Zstdlib::BEST_COMPRESSION, Zstdlib::MAX_WBITS, Zstdlib::MAX_MEM_LEVEL, Zstdlib::HUFFMAN_ONLY)

begin
  open "big.file" do |big_io|
    until big_io.eof? do
      compressed_io << zd.deflate(big_io.read(16384))
    end
  end
ensure
  deflate.close
end

end

While this example will work, for best optimization review the flags for your specific time, memory usage and output space requirements.



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# File 'ext/zstdlib/ruby/zlib-2.6/zstdlib.c', line 1555

static VALUE
rb_deflate_initialize(int argc, VALUE *argv, VALUE obj)
{
    struct zstream *z;
    VALUE level, wbits, memlevel, strategy;
    int err;

    rb_scan_args(argc, argv, "04", &level, &wbits, &memlevel, &strategy);
    TypedData_Get_Struct(obj, struct zstream, &zstream_data_type, z);

    err = deflateInit2(&z->stream, ARG_LEVEL(level), Z_DEFLATED,
		       ARG_WBITS(wbits), ARG_MEMLEVEL(memlevel),
		       ARG_STRATEGY(strategy));
    if (err != Z_OK) {
	raise_zlib_error(err, z->stream.msg);
    }
    ZSTREAM_READY(z);

    return obj;
}