[Matroska-devel] Re: [png-list] Request for a hi-speed bitmap compression format standard

Adam M. Costello png.amc+0 at nicemice.net.RemoveThisWord
Thu Aug 14 05:00:10 CEST 2003


Christian HJ Wiesner <chris at matroska.org> wrote:

> Results - speed:
> 1)              lzo1x_1 decompression time: 1111.283ms, 89986.1 blocks/s
> 2)            lzo1x_999 decompression time: 1504.558ms, 66464.7 blocks/s
> 3)              zlib l1 decompression time: 13653.456ms, 7324.2 blocks/s
> 4)              zlib l9 decompression time: 13660.727ms, 7320.3 blocks/s
> 3)             bzlib l1 decompression time: 40515.699ms, 2468.2 blocks/s
> 4)             bzlib l9 decompression time: 39775.623ms, 2514.1 blocks/s

Note that this is a comparison of various decompressors, not a
comparison of the potential decompression speed of the corresponding
stream formats.

The zlib decompressor always checks the compressed stream for syntactic
validity, and always computes a checksum of the decompressed data.

The lzo decompressor that you used never checks the compressed stream
for syntactic validity, and can crash the program if fed an invalid
stream.  Furthermore, it does not compute a checksum.

If you want to get closer to the truth about the speed limitations
inherent in the formats, you might try using lzo1x_decompress_safe()
instead of lzo1x_decompress(), and try hacking the zlib decompressor to
omit the checksum calculation.

AMC



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