org.tikv.common.codec

Class MyDecimal

java.lang.Object

org.tikv.common.codec.MyDecimal

All Implemented Interfaces:

Serializable

public class MyDecimal
extends Object
implements Serializable

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
MyDecimal()
MyDecimal(int digitsInt, int digitsFrac, boolean negative, int[] wordBuf)

Method Summary

Modifier and Type	Method and Description
void	clear() Clears this instance.
int	frac() Returns fraction digits that counts how many digits after ".".
int	fromBin(int precision, int frac, int[] bin) Parses a decimal from binary string for given precision and frac.
void	fromDecimal(double value) Parses a decimal value from a string
void	fromString(String s) parser a decimal value from a string.
int	precision()
static int	readWord(int[] b, int size, int start) Reads a word from a array at given size.
BigDecimal	toBigDecimal()
int[]	toBin(int precision, int frac) ToBin converts decimal to its binary fixed-length representation two representations of the same length can be compared with memcmp with the correct -1/0/+1 result
long	toLong()
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

MyDecimal

public MyDecimal()

MyDecimal

public MyDecimal(int digitsInt,
                 int digitsFrac,
                 boolean negative,
                 int[] wordBuf)

Method Detail

readWord

public static int readWord(int[] b,
                           int size,
                           int start)

Reads a word from a array at given size.

Parameters:

b - b is source data of unsigned byte as int[]

size - is word size which can be used in switch statement.

start - start indicates the where start to read.

precision

public int precision()

frac

public int frac()

Returns fraction digits that counts how many digits after ".". frac() reflects the actual effective fraction without trailing zero

fromDecimal

public void fromDecimal(double value)

Parses a decimal value from a string

Parameters:

value - an double value

fromBin

public int fromBin(int precision,
                   int frac,
                   int[] bin)

Parses a decimal from binary string for given precision and frac.

Parameters:

precision - precision specifies total digits that this decimal will be..

frac - frac specifies how many fraction digits

bin - bin is binary string which represents a decimal value.

fromString

public void fromString(String s)

parser a decimal value from a string.

Parameters:

s - s is a decimal in string form.

toString

public String toString()

Overrides:

toString in class Object

toBin

public int[] toBin(int precision,
                   int frac)

ToBin converts decimal to its binary fixed-length representation two representations of the same length can be compared with memcmp with the correct -1/0/+1 result

PARAMS precision/frac - if precision is 0, internal value of the decimal will be used, then the encoded value is not memory comparable.

NOTE the buffer is assumed to be of the size decimalBinSize(precision, frac)

RETURN VALUE bin - binary value errCode - eDecOK/eDecTruncate/eDecOverflow

DESCRIPTION for storage decimal numbers are converted to the "binary" format.

This format has the following properties: 1. length of the binary representation depends on the {precision, frac} as provided by the caller and NOT on the digitsInt/digitsFrac of the decimal to convert. 2. binary representations of the same {precision, frac} can be compared with memcmp - with the same result as DecimalCompare() of the original decimals (not taking into account possible precision loss during conversion).

This binary format is as follows: 1. First the number is converted to have a requested precision and frac. 2. Every full digitsPerWord digits of digitsInt part are stored in 4 bytes as is 3. The first digitsInt % digitsPerWord digits are stored in the reduced number of bytes (enough bytes to store this number of digits - see dig2bytes) 4. same for frac - full word are stored as is, the last frac % digitsPerWord digits - in the reduced number of bytes. 5. If the number is negative - every byte is inverted. 5. The very first bit of the resulting byte array is inverted (because memcmp compares unsigned bytes, see property 2 above)

Example:

1234567890.1234

internally is represented as 3 words

1 234567890 123400000

(assuming we want a binary representation with precision=14, frac=4) in hex it's

00-00-00-01 0D-FB-38-D2 07-5A-EF-40

now, middle word is full - it stores 9 decimal digits. It goes into binary representation as is:

........... 0D-FB-38-D2 ............

First word has only one decimal digit. We can store one digit in one byte, no need to waste four:

01 0D-FB-38-D2 ............

now, last word. It's 123400000. We can store 1234 in two bytes:

01 0D-FB-38-D2 04-D2

So, we've packed 12 bytes number in 7 bytes. And now we invert the highest bit to get the final result:

81 0D FB 38 D2 04 D2

And for -1234567890.1234 it would be

7E F2 04 C7 2D FB 2D return a int array which represents a decimal value.

Parameters:

precision - precision for decimal value.

frac - fraction for decimal value.

clear

public void clear()

Clears this instance.

toLong

public long toLong()

toBigDecimal

public BigDecimal toBigDecimal()