How to store integer in fewest bits possible in Java

Question

I have numbers lower than 16 and I want to store them the smallest way possible. I currently convert my integer to a byte but I don't need the whole byte. I think I only need 4 bits to hold my number. I want to use as little of a byte as I can.

byte solutionLength = (byte) myArray.length;
return solutionLength;

myArray.length is always less than 12. How can I use as few bits to store to my variable solutionLength ?

Off topic: Any reason you need to worry about memory so much? Just curious — ZeldaZach, Jun 30 '17 at 02:53
Because I store about 800 million of the returned value in an array. @ZeldaZach — ProgrammingCuber, Jun 30 '17 at 02:54
[`BitSet`](https://docs.oracle.com/javase/8/docs/api/java/util/BitSet.html) — Elliott Frisch, Jun 30 '17 at 02:55
@ProgrammingCuber Maybe you should look into alternative methods as I'd never store _that_ many results in an array... can you possibly shed some light as to why you're doing this exactly? — ZeldaZach, Jun 30 '17 at 02:56
this array contains solutions lengths of branches in a search algorithm which searches 1.5 billion nodes total. Currently only need 800 million of the 1.5 billion. @ZeldaZach — ProgrammingCuber, Jun 30 '17 at 02:58
[`BitSet`](https://docs.oracle.com/javase/8/docs/api/java/util/BitSet.html) — Dawood ibn Kareem, Jun 30 '17 at 03:06
BitSet helps if you want to store 1-bit values; it doesn't help for 4-bit or n-bit values. — Erwin Bolwidt, Jun 30 '17 at 03:49

score 4 · Accepted Answer · answered Jun 30 '17 at 03:17

It's impossible to have data types lower than a byte in size. If you have multiple numbers to store you can do a trick: store two 4-bit values in one byte.

byte storage = (byte) (((byte)myArray.length << 4) | (byte)myArray2.length);

Here you store two numbers in one byte. To access them try:

byte myArrayLength = (byte) ((storage & 0xf0) >> 4);
byte myArrayLength2 = (byte) (storage & 0x0f);

But integer would be better solution for it by avoiding type conversions

score 3 · Answer 2 · answered Jun 30 '17 at 03:00

3

You can use byte array, each byte will hold two values - one in higher 4 bits and another in lower for bits. E.g. 0x1F holds 1 and F. And you need to create a class which will calculate values by index.

answered Jun 30 '17 at 03:00

Evgeniy Dorofeev

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How to store integer in fewest bits possible in Java

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