BitBuffer (Yamcs Core 3.4.2 API)

java.lang.Object
- org.yamcs.utils.BitBuffer

```
public class BitBuffer
extends Object
```
Allows to read bits from a byte array (byte[]) keeps a bit position and the extractions are relative to the position. It allows also to provide an offset (in bytes) inside the byte array and then the bit position is relative to the offset. Supported operations are - extract up to 64 bits into a long - big endian or little endian - extract a byte array (throws exception if the position is not at the beginning of a byte) - exact a byte (throws exception if the position is not at the beginning of a byte) Note on the Little Endian: it is designed to work on x86 architecture which uses internally little endian byte _and_ bit ordering but when accessing memory, full bytes are transferred in big endian order. For example when in C you have a 32 bit structure: struct S { unsigned int a: 3; unsigned int b: 12; unsigned int c: 17; } and you pack that in a packet by just reading the corresponding 4 bytes memory, you will get the following representation (0 is the most significant bit): b7 b8 b9 b10 b11 a0 a1 a2 c16 b0 b1 b2 b3 b4 b5 b6 c8 c9 c10 c11 c12 c13 c14 c15 c0 c1 c2 c3 c4 c5 c6 c7 To read this with this BitBuffer you would naturally do like this: BitBuffer bb = new BitBuffer(..., 0); bb.setOrder(LITTLE_ENDIAN); a = bb.getBits(3); b = bb.getBits(12); c = bb.getBits(17); Note how the first call (when the bb.position=0) reads the 3 bits at position 5 instead of those at position 0

Author:

nm

Constructor Summary

Constructors
Constructor and Description
`BitBuffer(byte[] b)` Creates a new bit buffer that wraps array b starting at offset 0
`BitBuffer(byte[] b, int offset)` Creates a new bit buffer that wraps the array b starting at offset (in bytes)

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`byte[]`	`array()`
`int`	`arrayLength()` returns the backing array length in bytes!
`long`	`getBits(int numBits)` reads numBits from the buffer and returns them into a long on the rightmost position.
`byte`	`getByte()` fast getByte - only works when position%8 = 0 - otherwise throws an IllegalStateException advances the position by 8 bits
`void`	`getByteArray(byte[] dst)` Copies bytes from the buffer to the given destination array.
`ByteOrder`	`getByteOrder()`
`int`	`getPosition()` get position in bits
`int`	`offset()` Returns the offset inside the byte array where this buffer starts
`int`	`remainingBytes()` Returns the remaining bytes from position until the end of the buffer.
`void`	`setByteOrder(ByteOrder order)`
`void`	`setPosition(int position)` set position in bits
`int`	`sizeInBits()` returns the size of the buffer (from the offset to the end of the byte array) in bits
`BitBuffer`	`slice()` Creates a new BitBuffer backed by the same array but with the offset set at the current position of this buffer Works only when position%8 = 0 - otherwise throws an IllegalStateException

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - BitBuffer
```
public BitBuffer(byte[] b)
```
    Creates a new bit buffer that wraps array b starting at offset 0
    
    Parameters:
    
    b -
  - BitBuffer
```
public BitBuffer(byte[] b,
                 int offset)
```
    Creates a new bit buffer that wraps the array b starting at offset (in bytes)
    
    Parameters:
    
    b -
    
    offset -
- Method Detail
  - getBits
```
public long getBits(int numBits)
```
    reads numBits from the buffer and returns them into a long on the rightmost position. numBits has to be max 64.
    
    Parameters:
    
    numBits -
    
    Returns:
  - getPosition
```
public int getPosition()
```
    get position in bits
    
    Returns:
    
    current position in bits
  - setPosition
```
public void setPosition(int position)
```
    set position in bits
    
    Parameters:
    
    position -
  - setByteOrder
```
public void setByteOrder(ByteOrder order)
```
  - getByteOrder
```
public ByteOrder getByteOrder()
```
  - getByte
```
public byte getByte()
```
    fast getByte - only works when position%8 = 0 - otherwise throws an IllegalStateException advances the position by 8 bits
    
    Returns:
    
    the byte at the current position
  - getByteArray
```
public void getByteArray(byte[] dst)
```
    Copies bytes from the buffer to the given destination array. Works only when position%8 = 0 - otherwise throws an IllegalStateException
    
    Parameters:
    
    dst - - destination array
  - sizeInBits
```
public int sizeInBits()
```
    returns the size of the buffer (from the offset to the end of the byte array) in bits
    
    Returns:
    
    size in bits
  - arrayLength
```
public int arrayLength()
```
    returns the backing array length in bytes!
    
    Returns:
    
    array length
  - slice
```
public BitBuffer slice()
```
    Creates a new BitBuffer backed by the same array but with the offset set at the current position of this buffer Works only when position%8 = 0 - otherwise throws an IllegalStateException
    
    Returns:
    
    new bit buffer
  - array
```
public byte[] array()
```
  - offset
```
public int offset()
```
    Returns the offset inside the byte array where this buffer starts
    
    Returns:
  - remainingBytes
```
public int remainingBytes()
```
    Returns the remaining bytes from position until the end of the buffer. Works only when position%8 = 0 - otherwise throws an IllegalStateException
    
    Returns:

Class BitBuffer

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

BitBuffer

BitBuffer

Method Detail

getBits

getPosition

setPosition

setByteOrder

getByteOrder

getByte

getByteArray

sizeInBits

arrayLength

slice

array

offset

remainingBytes