C# 4 bit data type [closed]

问题

Does C# have a 4 bit data type? I want to make a program with variables that waste the minimum amount of memory, because the program will consume a lot.

For example: I need to save a value that i know it will go from 0 to 10 and a 4 bit var can go from 0 to 15 and it's perfect. But the closest i found was the 8 bit (1 Byte) data type Byte.

I have the idea of creating a c++ dll with a custom data type. Something like nibble. But, if that's the solution to my problem, i don't know where to start, and what i have to do.

Limitations: Creating a Byte and splitting it in two is NOT an option.

回答1:

No, there is no such thing as a four-bit data type in c#.

Incidentally, four bits will only store a number from 0 to 15, so it doesn't sound like it is fit for purpose if you are storing values from 0 to 127. To compute the range of a variable given that it has N bits, use the formula (2^N)-1 to calculate the maximum. 2^4 = 16 - 1 = 15.

If you need to use a data type that is less than 8 bits in order to save space, you will need to use a packed binary format and special code to access it.

You could for example store two four-bit values in a byte using an AND mask plus a bit shift, e.g.

byte source = 0xAD;
var hiNybble = (source & 0xF0) >> 4; //Left hand nybble = A
var loNyblle = (source & 0x0F);      //Right hand nybble = D

Or using integer division and modulus, which works well too but maybe isn't quite as readable:

var hiNybble = source / 16;
var loNybble = source % 16;

And of course you can use an extension method.

static byte GetLowNybble(this byte input)
{
    return input % 16;
}

static byte GetHighNybble(this byte input)
{
    return input / 16;
}

var hiNybble = source.GetHighNybble();
var loNybble = source.GetLowNybble();

Storing it is easier:

var source = hiNybble * 16 + lowNybble;

Updating just one nybble is harder:

var source = source & 0xF0 + loNybble;        //Update only low four bits
var source = source & 0x0F + (hiNybble << 4); //Update only high bits

回答2:

A 4-bit data type (AKA Nib) only goes from 0-15. It requires 7 bits to go from 0-127. You need a byte essentially.

回答3:

No, C# does not have a 4-bit numeric data type. If you wish to pack 2 4-bit values in a single 8-bit byte, you will need to write the packing and unpacking code yourself.

回答4:

No, even boolean is 8 bits size.

You can use >> and << operators to store and read two 4 bit values from one byte.

https://msdn.microsoft.com/en-us/library/a1sway8w.aspx

https://msdn.microsoft.com/en-us/library/xt18et0d.aspx

回答5:

Depending on how many of your nibbles you need to handle and how much of an issue performance is over memory usage, you might want to have a look at the BitArray and BitVector32 classes. For passing around of values, you'd still need bigger types though.

~~Yet another option could also be StructLayout fiddling, ... beware of dragons though.~~

来源：https://stackoverflow.com/questions/42075537/c-sharp-4-bit-data-type

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