package zstandard
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doc/zstandard/Zstandard/index.html
Module ZstandardSource
zstd, short for Zstandard, is a fast lossless compression algorithm, targeting real-time compression scenarios at zlib-level and better compression ratios. The zstd compression library provides in-memory compression and decompression functions. The library supports compression levels from 1 up to max_compression_level () (currently 22). Levels >= 20, labeled `--ultra`, should be used with caution, as they require more memory.
Compression can be done in:
- a single step (described as Simple API)
- a single step, reusing a context (described as Explicit context)
- unbounded multiple steps (described as Streaming compression)
The compression ratio achievable on small data can be highly improved using a dictionary in:
- a single step (described as Simple dictionary API)
- a single step, reusing a dictionary (described as Bulk-processing dictionary API)
Also see LZ4.
Might be raised when decompressing a message using a single pass decompression function.
Decompressed size is an optional field of compressed messages, but is always present when using a single-pass function such as Simple.compress, With_explicit_content.comprss, Simple_dictionary.compress and With_bulk_dictionary.compress. If the decompressed size is not present in the message, it might be necessary to use streaming mode to decompress the message.
Might be raised when decompressing a message using a single pass decompression function, indicating an error when inspecting the message -- for instance, invalid magic numbers.
Compression / decompression functions below might raise this exception if the return value they are passed does not have enough capacity. The argument is the required capacity.
The size of compressed messages is encoded in as a 64 bit integers. This OCaml library internally uses Int.t to represent size and can't decode messages whose sizes would not fit on an int. For those messages, decompression using the streaming mode is recommended.
Returns the max possible value for compression_level
compression_output_size_bound x is the maximum possible output size when doing a a single-pass compression of an input of size x.
(Single pass means something like Simple.compress; maximum possible means the worst case of the compression algorithm.).
Returns the decompressed size of a message. Since decompressed size is an optional field of compressed message, it might raise Content_size_unknown, Content_size_error or Error.
This module implements compression and decompression with explicitly managed contexts. When compressing or decompressing many times, it is recommended to allocate a context just once, and re-use it for each successive compression operation. This will make workload friendlier for system's memory.