How to read bits from file or extract bits from Byte? (1 bit Boolean, variable-bits Integer?)

[Nikolay Tsutsarin]

For example. I have a binary file with following written into it:

- 1 bit (Boolean)

- 1 bit (Boolean)

- 2 bit (Integer)

- 12 bit (Integer)

In parens are types which I want to read from this file.

[Hugh]

You can only read whole bytes from a file.

So it depends how the bits are laid-out.  Looks like you have a 16-bit number so it could be stored as 2 bytes.

If you are using the haxe.io.Input api, it might look like this:

// Assume little-endian - low first...

var low = input.readByte();

var high = input.readByte(); 

The it might be:

var bool0 = ( high & 0x80 ) > 0;

var bool1 = ( high & 0x40 ) > 0; 

var miniInt = ( high & 0x30 ) >> 4;

var int12 = ((high & 0x0f) << 8 ) | low;

But it really depends on how the bits are on the file.

[Nikolay Tsutsarin]

Wow, awesome, so fast reply!

I have big endian encoding according to documentation, so how I have to change the code?

Also, I know almost nothing about system and low-level programming, where I can read theory primary on working with bits, bytes, endians and so on?

[Juraj Kirchheim]

Swap the two first lines of code:

// Assume big-endian - high first...

var high = input.readByte(); 

var low = input.readByte();

Best,

Juraj

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[Nikolay Tsutsarin]

Everything works, thank you!

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