bit-coder

A node.js library for bitwise binary encoding of data

Usage

var assert = require('assert');
var bitCoder = require('bit-coder');

// 1000 bits to write to.
var wbs = new bitCoder.BitStream(1000);

// Write out some values.
wbs.writeBits(100, 20);
wbs.writeUnary(20);
wbs.writeEliasGamma(2000);

// Pad and get the result
var buf = wbs.wrap();

// Get a new bitstream removing the padding
var rbs = bitCoder.BitStream.unwrap(buf);

// Check the contents.
assert.equal(rbs.readBits(20), 100);
assert.equal(rbs.readUnary(), 20);
assert.equal(rbs.readEliasGamma(), 2000);

API

BitStream

new bitCoder.BitStream(len)

Construct a new BitStream backed by a new BitBuffer len bits.

new bitCoder.BitStream(bitbuf)

Construct a new BitStream backed by an existing BitBuffer.

new bitCoder.BitStream(buf, len)

Construct a new BitStream backed by an new BitBuffer constructed from the existing buffer and optional length.

bitCoder.Bitstream.unwrap(buf)

Construct a new BitStream from of buffer previously obtained from calling wrap. This is a Function method, not a prototype method.

BitStream.index

The current read/write pointer; change this to seek.

BitStream.view

The underling BitBuffer.

BitStream.wrap()

Pad a bit stream with 1 to 8 bits to the nearest byte boundary and return the slice of the underling Buffer that was written.

Bitstream.readBits(len)

Read len bits (32 maximum) from the stream.

Bitstream.writeBits(offset, len)

Write len (32 maximum) to the stream.

Bitstream.fillBits(offset, v, len)

Write len bits with the lowest bit of v.

BitStream.writeUnary(v)

Write out the given value (v >= 1) in unary encoding

BitStream.readUnary()

Read a unary encoded value from the stream

BitStream.writeEliasGamma/writeEliasDelta/writeEliasOmega/writeFibonacci(v)

Write out the given value (v >= 1) in the indicated universal code

BitStream.readEliasGamma/readEliasDelta/readEliasOmega/readFibonacci()

Read a value encoded with the indicated universal code

BitStream.writeTruncateBinary(v, n)

Write out the value v (0 <= v < n) in base n truncated binary representation

BitStream.readTruncateBinary(n)

Read a base n truncated binary value from the stream

BitBuffer

new bitCoder.BitBuffer(len)

Construct a new BitBuffer len bits long backed by a Buffer on node.js or a Uint8Array in the browser.

new bitCoder.BitBuffer(buffer, len)

Construct a new BitBuffer backed by the supplied Buffer or Uint8Array. The length is specified by the optional len, which is all the bits in the buffer if unspecified.

BitBuffer.getBits(offset, len)

Retreive len bits (32 maximum) from the buffer at the supplied offset.

BitBuffer.setBits(offset, len)

Set len (32 maximum) to the buffer at the supplied offset.

BitBuffer.fillBits(offset, v, len)

Fill len bits with the lowest bit of v at the supplied offset.

License

MIT