zstandard v0.17.0 (latest)

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.

exception Error of string

exception Content_size_unknown

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.

exception Content_size_error

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.

exception Not_enough_capacity of int

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.

exception Decompressed_size_exceeds_max_int of Core.Int64.t

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.

val max_compression_level : unit -> int

Returns the max possible value for compression_level

val compression_output_size_bound : Core.Int64.t -> Core.Int64.t

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.).

module Output : sig ... end

module Input : sig ... end

val decompressed_size : Input.t -> Core.Int64.t

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.

module Compression_context : sig ... end

module Decompression_context : sig ... end

module Simple : sig ... end

module With_explicit_context : sig ... end

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.

module Dictionary : sig ... end

module Simple_dictionary : sig ... end

module Bulk_processing_dictionary : sig ... end

module Streaming : sig ... end

The functions exposed in this module differ from the rest of the library, and operates on stream of data (rather than on single messages). Therefore, the API is more complex, and does not use the Input module.

package zstandard