@damienvesper/bit-buffer

BitBuffer provides two objects, BitView and BitStream. BitView is a wrapper for ArrayBuffers, similar to JavaScript's DataView, but with support for bit-level reads and writes. BitStream is a wrapper for a BitView used to help maintain your current buffer position, as well as to provide higher-level read / write operations such as for ASCII strings.

BitView

Attributes

bb.buffer  // Underlying ArrayBuffer.

bb.bigEndian = true; // Switch to big endian (default is little)

Methods

BitView(buffer, optional byteOffset, optional byteLength)

Default constructor, takes in a single argument of an ArrayBuffer. Optional are the byteOffset and byteLength arguments to offset and truncate the view's representation of the buffer.

getBits(offset, bits, signed)

Reads bits number of bits starting at offset, twiddling the bits appropriately to return a proper 32-bit signed or unsigned value. NOTE: While JavaScript numbers are 64-bit floating-point values, we don't bother with anything other than the first 32 bits.

getInt8, getUint8, getInt16, getUint16, getInt32, getUint32(offset)

Shortcuts for getBits, setting the correct bits / signed values.

getFloat32(offset)

Gets 32 bits from offset, and coerces and returns as a proper float32 value.

getFloat64(offset)

Gets 64 bits from offset, and coerces and returns as a proper float64 value.

setBits(offset, value, bits)

Sets bits number of bits at offset.

setInt8, setUint8, setInt16, setUint16, setInt32, setUint32(offset)

Shortcuts for setBits, setting the correct bits count.

setFloat32(offset)

Coerces a float32 to uint32 and sets at offset.

setFloat64(offset)

Coerces a float64 to two uint32s and sets at offset.

BitStream

Attributes

bb.byteIndex; // Get current index in bytes.
bb.byteIndex = 0;  // Set current index in bytes.

bb.view;  // Underlying BitView

bb.length; // Get the length of the stream in bits

bb.bitsLeft; // The number of bits left in the stream

bb.index; // Get the current index in bits
bb.index = 0; // Set the current index in bits

bb.bigEndian = true; // Switch to big endian (default is little)

Methods

BitStream(view)

Default constructor, takes in a single argument of a BitView, ArrayBuffer or node Buffer.

BitSteam(buffer, optional byteOffset, optional byteLength)

Shortcut constructor that initializes a new BitView(buffer, byteOffset, byteLength) for the stream to use.

readBits(bits, signed)

Returns bits numbers of bits from the view at the current index, updating the index.

writeBits(value, bits)

Sets bits numbers of bits from value in the view at the current index, updating the index.

readUint8(), readUint16(), readUint32(), readInt8(), readInt16(), readInt32()

Read a 8, 16 or 32 bits (unsigned) integer at the current index, updating the index.

writeUint8(value), writeUint16(value), writeUint32(value), writeInt8(value), writeInt16(value), writeInt32(value)

Write 8, 16 or 32 bits from value as (unsigned) integer at the current index, updating the index.

readFloat32(), readFloat64()

Read a 32 or 64 bit floating point number at the current index, updating the index.

writeFloat32(value), writeFloat64()

Set 32 or 64 bits from value as floating point value at the current index, updating the index.

readBoolean()

Read a single bit from the view at the current index, updating the index.

writeBoolean(value)

Write a single bit to the view at the current index, updating the index.

readASCIIString(optional bytes), readUTF8String(optional bytes)

Reads bytes from the underlying view at the current index until either bytes count is reached or a 0x00 terminator is reached.

writeASCIIString(string, optional bytes), writeUTF8String(string, optional bytes)

Writes a string followed by a NULL character to the underlying view starting at the current index. If the string is longer than bytes it will be truncated, and if it is shorter 0x00 will be written in its place.

readBitStream(length)

Create a new BitStream from the underlying view starting the the current index and a length of length bits. Updating the index of the existing BitStream

readArrayBuffer(byteLength)

Read byteLength bytes of data from the underlying view as ArrayBuffer, updating the index.

License

MIT