Crate bitvec[−][src]

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Addressable Bits

bitvec is a foundation library for memory compaction techniques that rely on viewing memory as bit-addressed rather than byte-addressed.

The bitvec project is designed to provide a comprehensive set of tools for users who need memory compaction, with as low a cost as possible.

Usage

bitvec provides data structures that specialize the major sequence types in the standard library:

[bool] becomes BitSlice
[bool; N] becomes BitArray
Box<[bool]> becomes BitBox
Vec<bool> becomes BitVec

You can start using the crate in an existing codebase by replacing types and chasing compiler errors from there.

As an example,

let mut io_buf: Vec<u8> = Vec::new();
io_buf.extend(&[0x47, 0xA5]);

let mut stats: Vec<bool> = Vec::new();
stats.extend(&[true, false, true, true, false, false, true, false]);

would become

use bitvec::prelude::*;

let mut io_buf = bitvec![Msb0, u8; 0; 16];
io_buf[.. 4].store(4u8);
io_buf[4 .. 8].store(7u8);
io_buf[8 .. 16].store(0xA5u8);

let mut stats: BitVec = BitVec::new();
stats.extend(&[true, false, true, true, false, false, true, false]);

Capabilities

bitvec stands out from other bit-vector libraries, both in Rust and in other languages, in a few significant ways.

Unlike other Rust libraries, bitvec stores its information in pointers to memory regions, rather than in the region directly. By using its own pointer encoding scheme, it can use references &BitSlice and &mut BitSlice to manage memory and fit seamlessly into the Rust language rules and API signatures.

Unlike any other bit-sequence system, bitvec enables users to specify the register element type used to store data, and the ordering of bits within those elements. This sidesteps the problems found in C bitfields, C++ std::bitset, Python bitstring, Erlang bitstream, and Rust libraries such as bit-vec.

By permitting the in-memory layout to be specified by the user, rather than within the library, users are able to have the behavior characteristics they want without effort or workarounds.

This works by suppling two type parameters: O: BitOrder specifies the ordering of bits within a register element, and T: BitStore specifies which register element is used to store bits. T is restricted to be only the unsigned integers, and Cell or Atomic variants of them.

bitvec correctly handles memory aliasing by leveraging the type system to mark regions that have become subject to concurrency and either force the use of atomic memory accesses or forbid simultaneous multiprocessing. You will never need to insert your own guards to prevent race conditions, and BitSlice provides APIs to separate any slice into its aliased and unaliased sub-regions.

Library Structure

You should generally import the library prelude, with

use bitvec::prelude::*;

The prelude contains all the symbols you will need to make use of the crate. Almost all begin with the prefix Bit; only the orderings Lsb0 and Msb0 do not. This will reduce the likelihood of name collisions. See the prelude module documentation for more detail on which symbols are imported, and how you can more precisely control this.

Each major component in the library is divided into its own module. This includes each data structure and trait, as well as utility objects used for implementation. The data structures that mirror the language distribution have submodules for each part of their mirroring: api ports inherent methods, iter contains iteration logic, ops operator overrides, and traits all other trait implementations.The data structure’s own module only contains its own definition and its inherent methods that are not ports of the standard libraries.

Usage

As a replacement for bool data structures, you should be able to replace old type definition and value construction sites with their corresponding items from this crate, and the rest of your project should just work with the new types.

To use bitvec for bitfields, use BitArray or BitVec to manage your data buffers (compile-time static and run-time dynamic, respectively), and the BitField trait to manage transferring values into and out of them.

The BitSlice type contains most of the methods and trait implementations used to interact with the contents of a memory buffer. BitVec adds methods for operating on allocations, and specializes BitSlice methods that can take advantage of owned buffers.

The domain module, whose types are accessed by the .{bit_,}domain{,_mut} methods on BitSlice, allows users to split their views of memory on aliasing boundaries, removing synchronization where provably safe.

There are many ways to construct a bit-level view of data. The BitArray, BitBox, and BitVec types are all owning types that contain a buffer of memory and dereference to BitSlice in order to view it. In addition, you can borrow any piece of ordinary Rust memory as a BitSlice view using its borrowing constructor functions, and the BitView trait methods.