Class FormatableBitSet
java.lang.Object
org.apache.derby.iapi.services.io.FormatableBitSet
- All Implemented Interfaces:
Externalizable
,Serializable
,Cloneable
,Formatable
,TypedFormat
FormatableBitSet is implemented as a packed array of bytes.
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprivate byte
private int
private byte[]
Bits are stored as an array of bytes. -
Constructor Summary
ConstructorsConstructorDescriptionNiladic ConstructorFormatableBitSet
(byte[] newValue) Constructs a Bit from an array of bytes.FormatableBitSet
(int numBits) Constructs a Bit with the initial number of bitsFormatableBitSet
(FormatableBitSet original) Copy constructor -
Method Summary
Modifier and TypeMethodDescriptionvoid
and
(FormatableBitSet otherBit) Bitwise AND this FormatableBitSet with another FormatableBitSet.int
If any bit is set, return the zero-based bit index of the first bit that is set.int
anySetBit
(int beyondBit) Like anySetBit(), but return any set bit whose number is bigger than beyondBit.private int
calculateLength
(int realByteLength) private final void
checkPosition
(int p) void
clear()
Clear all the bits in this FormatableBitSetvoid
clear
(int position) Bit clearclone()
int
compare
(FormatableBitSet other) Bit comparison.void
copyFrom
(FormatableBitSet that) Copy the bytes from another FormatableBitSet.boolean
Bit equivalence.private static byte
firstSet
(byte v) A utility method which treats the byte argument as an 8-bit bitset and finds the first set bit in that byte.final boolean
get
(int position) Bit get -- alias for isSet()byte[]
Get the value of the byte arrayint
Get the length in bitsint
Get the length in bytes of a Bit valueint
Get a count of the number of bits that are set.int
Get the formatID which corresponds to this class.void
grow
(int n) Grow (widen) a FormatableBitSet so that it contains at least N bits.int
hashCode()
Produce a hash code by putting the value bytes into an int, exclusive OR'ing if there are more than 4 bytes.private void
initializeBits
(int numBits) boolean
This method returns true if the following conditions hold: 1.final boolean
isSet
(int position) Bit isSetstatic int
maxBitsForSpace
(int numBytes) Statically calculates how many bits can fit into the number of bytes if this Bit object is externalized.private static byte
numBitsInLastByte
(int bits) Figure out how many bits are in the last byte from the total number of bits.private static int
numBytesFromBits
(int bits) Figure out how many bytes are needed to store the input number of bits.void
or
(FormatableBitSet otherBit) Bitwise OR this FormatableBitSet with another FormatableBitSet.void
Note: gracefully handles zero length bits -- will create a zero length array with no bits being used.void
set
(int position) Bit setvoid
shrink
(int n) Shrink (narrow) a FormatableBitSet to N bits.int
size()
Get the length in bits -- alias for getLength()toString()
Format the string into BitSet format: {0, 2, 4, 8} if bits 0, 2, 4, 8 are set.private static int
udiv8
(int i) private static byte
umod8
(int i) private static int
umul8
(int i) void
Format: int length in bits byte[]void
xor
(FormatableBitSet otherBit) Bitwise XOR this FormatableBitSet with another FormatableBitSet.
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Field Details
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value
private byte[] valueBits are stored as an array of bytes. Bits are numbered starting at 0. Bits 0..7 go in byte[0], 8..15 in byte[1] and so on. The number of bytes is tracked as part of the byte array. The number of bits being used is derived by the number of bytes being used and the number of bits being used by the last byte. The partially unused byte is always byte[byte.length] with the lowest bits being unused. Zero length bits are stored using a zero length byte array, with all bits marked as unused. -
bitsInLastByte
private byte bitsInLastByte -
lengthAsBits
private transient int lengthAsBits
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Constructor Details
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FormatableBitSet
public FormatableBitSet()Niladic Constructor -
FormatableBitSet
public FormatableBitSet(int numBits) Constructs a Bit with the initial number of bits -
FormatableBitSet
public FormatableBitSet(byte[] newValue) Constructs a Bit from an array of bytes. Assume bytes are all being used.- Parameters:
newValue
- The array of bytes to make up the new Bit
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FormatableBitSet
Copy constructor- Parameters:
original
- the FormatableBitSet to make a copy from
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Method Details
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checkPosition
private final void checkPosition(int p) -
udiv8
private static int udiv8(int i) -
umod8
private static byte umod8(int i) -
umul8
private static int umul8(int i) -
initializeBits
private void initializeBits(int numBits) -
clone
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invariantHolds
public boolean invariantHolds()This method returns true if the following conditions hold: 1. The number of bits in the bitset will fit into the allocated byte array. 2. 'lengthAsBits' and 'bitsInLastByte' are consistent. 3. All unused bits in the byte array are unset. This represents an invariant for the class, so this method should always return true. The method is public, but is primarily intended for testing and ASSERTS.- Returns:
- true if invariant holds, false otherwise
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getLengthInBytes
public int getLengthInBytes()Get the length in bytes of a Bit value- Returns:
- The length in bytes of this value
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getLength
public int getLength()Get the length in bits- Returns:
- The length in bits for this value NOTE: could possibly be changed to a long. As is we are restricted to 2^(31-3) -> 256meg instead of 2^31 (Integer.MAX_VALUE) like other datatypes (or 2 gig). If it is ever changed to a long be sure to change read/writeExternal which write out the length in bits.
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calculateLength
private int calculateLength(int realByteLength) -
size
public int size()Get the length in bits -- alias for getLength()- Returns:
- The length in bits for this value
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getByteArray
public byte[] getByteArray()Get the value of the byte array- Returns:
- The value of the byte array
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grow
public void grow(int n) Grow (widen) a FormatableBitSet so that it contains at least N bits. If the bitset already has more than n bits, this is a noop. Negative values of n are not allowed. ASSUMPTIONS: that all extra bits in the last byte are zero.- Parameters:
n
- The number of bits you want. The bits are always added as 0 and are appended to the least significant end of the bit array.
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shrink
public void shrink(int n) Shrink (narrow) a FormatableBitSet to N bits. N may not be larger than the current bitset size, or negative.- Parameters:
n
- The number of bits the caller wants. The bits are always removed from the least significant end of the bit array.
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equals
Bit equivalence. Compare this with other. If the length is different, then cannot be equal so short circuit. Otherwise, rely on compare(). Note that two zero length bits are considered equal. -
compare
Bit comparison. Compare this with other. Will always do a byte by byte compare. Given 2 similar bits of unequal lengths (x and y), where x.getLength() < y.getLength() but where: x[0..x.getLength()] == y[0..x.getLength()] then x < y.- Parameters:
other
- the other bit to compare to- Returns:
- -1 - if other < this 0 - if other == this 1 - if other > this
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hashCode
public int hashCode()Produce a hash code by putting the value bytes into an int, exclusive OR'ing if there are more than 4 bytes. -
isSet
public final boolean isSet(int position) Bit isSet- Parameters:
position
- the bit to check
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get
public final boolean get(int position) Bit get -- alias for isSet()- Parameters:
position
- the bit to check
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set
public void set(int position) Bit set- Parameters:
position
- the bit to set
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clear
public void clear(int position) Bit clear- Parameters:
position
- the bit to clear
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clear
public void clear()Clear all the bits in this FormatableBitSet -
numBytesFromBits
private static int numBytesFromBits(int bits) Figure out how many bytes are needed to store the input number of bits.- Parameters:
bits
- bits- Returns:
- the number of bytes
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numBitsInLastByte
private static byte numBitsInLastByte(int bits) Figure out how many bits are in the last byte from the total number of bits.- Parameters:
bits
- bits- Returns:
- the number of bits
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toString
Format the string into BitSet format: {0, 2, 4, 8} if bits 0, 2, 4, 8 are set. -
maxBitsForSpace
public static int maxBitsForSpace(int numBytes) Statically calculates how many bits can fit into the number of bytes if this Bit object is externalized. Only valid for this implementation of Bit. -
firstSet
private static byte firstSet(byte v) A utility method which treats the byte argument as an 8-bit bitset and finds the first set bit in that byte. Assumes that at least one bit in v is set (v!=0).- Parameters:
v
- a non-zero byte to check for set bits- Returns:
- the zero-based index of the first set bit in the argument byte
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anySetBit
public int anySetBit()If any bit is set, return the zero-based bit index of the first bit that is set. If no bit is set, return -1. By using anySetBit() and anySetBit(beyondBit), one can quickly go thru the entire bit array to return all set bit.- Returns:
- the zero-based index of the first bit that is set, or -1 if no bit is set
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anySetBit
public int anySetBit(int beyondBit) Like anySetBit(), but return any set bit whose number is bigger than beyondBit. If no bit is set after beyondBit, -1 is returned. By using anySetBit() and anySetBit(beyondBit), one can quickly go thru the entire bit array to return all set bit.- Parameters:
beyondBit
- Only look at bit that is greater than this bit number. Supplying a value of -1 makes the call equivalent to anySetBit().- Returns:
- the bit number of a bit that is set, or -1 if no bit after beyondBit is set
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or
Bitwise OR this FormatableBitSet with another FormatableBitSet. The result is stored in this bitset. The operand is unaffected. A null operand is treated as an empty bitset (i.e. a noop). A bitset that is smaller than its operand is expanded to the same size.- Parameters:
otherBit
- bitset operand
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copyFrom
Copy the bytes from another FormatableBitSet. Assumes that this bit set is at least as large as the argument's bit set. -
and
Bitwise AND this FormatableBitSet with another FormatableBitSet. The result is stored in this bitset. The operand is unaffected. A null operand is treated as an empty bitset (i.e. clearing this bitset). A bitset that is smaller than its operand is expanded to the same size.- Parameters:
otherBit
- bitset operand
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xor
Bitwise XOR this FormatableBitSet with another FormatableBitSet. The result is stored in this bitset. The operand is unaffected. A null operand is treated as an empty bitset (i.e. a noop). A bitset that is smaller than its operand is expanded to the same size.- Parameters:
otherBit
- bitset operand
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getNumBitsSet
public int getNumBitsSet()Get a count of the number of bits that are set.- Returns:
- The number of bits that are set.
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writeExternal
Format:- int length in bits
- byte[]
- Specified by:
writeExternal
in interfaceExternalizable
- Throws:
IOException
- See Also:
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readExternal
Note: gracefully handles zero length bits -- will create a zero length array with no bits being used. Fortunately in.read() is ok with a zero length array so no special code.WARNING: this method cannot be changed w/o changing SQLBit because SQLBit calls this directly w/o calling read/writeObject(), so the format id is not stored in that case.
- Specified by:
readExternal
in interfaceExternalizable
- Throws:
IOException
- See Also:
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getTypeFormatId
public int getTypeFormatId()Get the formatID which corresponds to this class.- Specified by:
getTypeFormatId
in interfaceTypedFormat
- Returns:
- the formatID of this class
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