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diff --git a/app/lzo/doc/LZO.FAQ b/app/lzo/doc/LZO.FAQ deleted file mode 100644 index cb1f38aa..00000000 --- a/app/lzo/doc/LZO.FAQ +++ /dev/null @@ -1,213 +0,0 @@ -============================================================================ -LZO Frequently Asked Questions -============================================================================ - - -I hate reading docs - just tell me how to add compression to my program -======================================================================= - -This is for the impatient: take a look at examples/simple.c and -examples/lzopack.c and see how easy this is. - -But you will come back to read the documentation later, won't you ? - - -Can you explain the naming conventions of the algorithms ? -========================================================== - -Let's take a look at LZO1X: - - The algorithm name is LZO1X. - The algorithm category is LZO1. - Various compression levels are implemented. - - LZO1X-999 - !---------- algorithm category - !--------- algorithm type - !!!----- compression level (1-9, 99, 999) - - LZO1X-1(11) - !---------- algorithm category - !--------- algorithm type - !------- compression level (1-9, 99, 999) - !!---- memory level (memory requirements for compression) - -All compression/memory levels generate the same compressed data format, -so e.g. the LZO1X decompressor handles all LZO1X-* compression levels -(for more information about the decompressors see below). - -Category LZO1 algorithms: compressed data format is strictly byte aligned -Category LZO2 algorithms: uses bit-shifting, slower decompression - - -Why are there so many algorithms ? -================================== - -Because of historical reasons - I want to support unlimited -backward compatibility. - -Don't get misled by the size of the library - using one algorithm -increases the size of your application by only a few KiB. - -If you just want to add a little bit of data compression to your -application you may be looking for miniLZO. -See minilzo/README.LZO for more information. - - -Which algorithm should I use ? -============================== - -LZO1X seems to be best choice in many cases, so: -- when going for speed use LZO1X-1 -- when generating pre-compressed data use LZO1X-999 -- if you have little memory available for compression use LZO1X-1(11) - or LZO1X-1(12) - -Of course, your mileage may vary, and you are encouraged to run your -own experiments. Try LZO1Y and LZO1F next. - - -What's the difference between the decompressors per algorithm ? -=============================================================== - -Once again let's use LZO1X for explanation: - -- lzo1x_decompress - The 'standard' decompressor. Pretty fast - use this whenever possible. - - This decompressor expects valid compressed data. - If the compressed data gets corrupted somehow (e.g. transmission - via an erroneous channel, disk errors, ...) it will probably crash - your application because absolutely no additional checks are done. - -- lzo1x_decompress_safe - The 'safe' decompressor. Somewhat slower. - - This decompressor will catch all compressed data violations and - return an error code in this case - it will never crash. - -- lzo1x_decompress_asm - Same as lzo1x_decompress - written in assembler. - -- lzo1x_decompress_asm_safe - Same as lzo1x_decompress_safe - written in assembler. - -- lzo1x_decompress_asm_fast - Similar to lzo1x_decompress_asm - but even faster. - - For reasons of speed this decompressor can write up to 3 bytes - past the end of the decompressed (output) block. - [ technical note: because data is transferred in 32-bit units ] - - Use this when you are decompressing from one memory block to - another memory block - just provide output space for 3 extra bytes. - You shouldn't use it if e.g. you are directly decompressing to video - memory (because the extra bytes will be show up on the screen). - -- lzo1x_decompress_asm_fast_safe - This is the safe version of lzo1x_decompress_asm_fast. - - -Notes: ------- -- When using a safe decompressor you must pass the number of - bytes available in 'dst' via the parameter 'dst_len'. - -- If you want to be sure that your data is not corrupted you must - use a checksum - just using the safe decompressor is not enough, - because many data errors will not result in a compressed data violation. - -- Assembler versions are only available for the i386 family yet. - Please see also asm/i386/00README.TXT - -- You should test if the assembler versions are actually faster - than the C version on your machine - some compilers can do a very - good optimization job and they also can optimize the code - for a specific processor. - - -What is this optimization thing ? -================================= - -The compressors use a heuristic approach - they sometimes code -information that doesn't improve compression ratio. - -Optimization removes this superfluos information in order to -increase decompression speed. - -Optimization works similar to decompression except that the -compressed data is modified as well. The length of the compressed -data block will not change - only the compressed data-bytes will -get rearranged a little bit. - -Don't expect too much, though - my tests have shown that the -optimization step improves decompression speed by about 1-3%. - - -I need even more decompression speed... -======================================= - -Many RISC processors (like MIPS) can transfer 32-bit words much -faster than bytes - this can significantly speed up decompression. -So after verifying that everything works fine you can try if activating -the LZO_ALIGNED_OK_4 macro improves LZO1X and LZO1Y decompression -performance. Change the file config.h accordingly and recompile everything. - -On an i386 architecture you should evaluate the assembler versions. - - -How can I reduce memory requirements when (de)compressing ? -=========================================================== - -If you cleverly arrange your data, you can do an overlapping (in-place) -decompression which means that you can decompress to the *same* -block where the compressed data resides. This effectively removes -the space requirements for holding the compressed data block. - -This technique is essential e.g. for usage in an executable packer. - -You can also partly overlay the buffers when doing compression. - -See examples/overlap.c for a working example. - - -Can you give a cookbook for using pre-compressed data ? -======================================================= - -Let's assume you use LZO1X-999. - -1) pre-compression step - - call lzo_init() - - call lzo1x_999_compress() - - call lzo1x_optimize() - - compute an adler32 checksum of the *compressed* data - - store the compressed data and the checksum in a file - - if you are paranoid you should verify decompression now - -2) decompression step within your application - - call lzo_init() - - load your compressed data and the checksum - - optionally verify the checksum of the compressed data - (so that you can use the standard decompressor) - - decompress - -See examples/precomp.c and examples/precomp2.c for a working example. - - -How much can my data expand during compression ? -================================================ - -LZO will expand incompressible data by a little amount. -I still haven't computed the exact values, but I suggest using -these formulas for a worst-case expansion calculation: - - Algorithm LZO1, LZO1A, LZO1B, LZO1C, LZO1F, LZO1X, LZO1Y, LZO1Z: - ---------------------------------------------------------------- - output_block_size = input_block_size + (input_block_size / 16) + 64 + 3 - - [This is about 106% for a large block size.] - - Algorithm LZO2A: - ---------------- - output_block_size = input_block_size + (input_block_size / 8) + 128 + 3 - |