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:
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:
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_c/ruby/zlib-3.2/zstdlib.c', line 1665 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; } |