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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.

driconmax
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    The smallest addressable space is a byte, so no, you can't have a half byte variable. – NathanOliver Feb 06 '17 at 19:18
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    you'll have a lot of overhead. – Daniel A. White Feb 06 '17 at 19:18
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    If you are worried about having so many 4-bit values that you'll exhaust memory, then you are probably trying to solve this problem the wrong way. – Joe Feb 06 '17 at 19:19
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    What is "consume a lot"? 2 GB? 4 GB? 64 GB? Whatever you are looking at, you are probably thinking about this too soon and/or solving the problem the wrong way. – crashmstr Feb 06 '17 at 19:20
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    I need to save memory from all the places that i can. – driconmax Feb 06 '17 at 19:20
  • It sounds like you need a byte anyway to store 0-127. But if you need to work with nibbles, look here: http://stackoverflow.com/questions/3124960/how-can-you-nibble-nybble-bytes-in-c – Icemanind Feb 06 '17 at 19:21
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    Why the downvotes? I just want to know something that i don't... – driconmax Feb 06 '17 at 19:26
  • "Creating a Byte and splitting it in two is NOT an option." I'll let you have three guesses at what any compiler faced with the task of offering a 4-bit data type would *need to do* to support this on any modern processor, and the first two don't count. There's a really good reason why C# *doesn't* offer you this (nor any other kind of bit types like C does): bit bashing is hella slow. For most applications, consuming twice as much memory in exchange for running more than twice as fast would be totally worth it. For the few where it's not, you get to earn your wage by programming it. – Jeroen Mostert Feb 06 '17 at 20:07
  • Instead of thinking small, it may pay off to think big. Why do you need to store a lot of values in the range 0 to 10? Is that 10, inclusive or exclusive? Are these digits? Could you be using integer/`BigInteger` types to group these instead, and get a speed up of computation along with reduction of memory? If the 10 is inclusive, what about base 11 arithmetic? "I need to consume the minimum amount of memory" is almost certainly not a valid problem statement -- you need to consume an *effective* amount of memory for your actual problem, which may or may not be the minimum possible. – Jeroen Mostert Feb 06 '17 at 20:29
  • I have a program that simulates all the stars in the milky way. Having that loaded in memory, and rendered in the screen, consumes memory and cpu time, processing each value. So i think if had smaller variables i could solve some problems and leaving more memory to the double vars containing the stars positions – driconmax Feb 06 '17 at 20:41
  • There are about three orders of magnitude more stars in the Milky Way than you can hold data in memory for on most reasonable machines, barring compression techniques -- and of those that will fit in memory, there's many more than you'll be able to render. You really don't need to worry about solving the problem of storing numbers from 0 to 10 *just yet*. Effectively partitioning your data would be more likely to pay off. Or for that matter seeing where `float` would be enough (4 bytes as opposed to the 8 of a `double`). Identify what you are spending memory on first, before *nibbling* at it. – Jeroen Mostert Feb 06 '17 at 20:53
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    There are roughly 100 billion stars in the Milky Way. A standard for RAM in a modern desktop is 8 or 16 gigabytes, which is `17,179,869,184` bytes [at the most](https://en.wikipedia.org/wiki/Gibibyte). Assuming you used nibbles and packed the RAM full of nothing but star data, that still only lets you store about 34% of them, and that leaves nothing for the program as well as other low-priority things such as the operating system itself. I think you should really revisit the scope and requirements of your program. – Abion47 Feb 06 '17 at 21:45
  • I'd also be really curious how you planned on storing and simulating all the relevant information and behavior of a star, including but not limited to mass, 3D velocity, 3D position, 3D spin, composition, size, or number of satellites, all using only 4 bits of information. – Abion47 Feb 06 '17 at 21:52
  • The color of the star, spin, composition and bodies orbiting are not useful from a very far distance, so that's not loaded. I save a lot of memory in that. But when i get closer i have to render a lot of data, like the type of star, all the data you mention, pulse frequency between other info. For example, for the type of star, i only need a one digit number. For the type of the surface, i can use 15 types, and combine them. And for so many others things i need short numbers. That i thought it could help saving memory, and leaving it to the big data (double and floats) – driconmax Feb 07 '17 at 12:43
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    This is an excellent question, I do not know why you guys attacking the asker? yes, you can, just create a class or a struct containing 4 bool variables, and you program its methods such as convert to integer, printing, storing, etc. – Ahmad Hassanat May 27 '20 at 19:20

5 Answers5

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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
Community
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John Wu
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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.

VoteCoffee
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  • Yes, sorry, i mean 0 to 10. Fixing the question now – driconmax Feb 06 '17 at 19:23
  • http://stackoverflow.com/questions/3124960/how-can-you-nibble-nybble-bytes-in-c – VoteCoffee Feb 06 '17 at 19:24
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    If you only need 0-10, you can compact 2 nibs in a byte. But honestly, all of this is bad practice in a managed environment. You should really consider what you're trying to accomplish. Programming in a managed environment really is more concerned with abstraction and decoupling from implementation hardware. If you were looking for the answer in C++ it would make more sense to me. – VoteCoffee Feb 06 '17 at 19:26
  • @VoteCoffee `Limitations: Creating a Byte and splitting it in two is NOT an option.` – driconmax Feb 06 '17 at 19:29
  • You'll likely need to create a helper class to marshall your work into unmanaged code. If you try to roll your own nibble using booleans, then you'll end up using more memory space. Even in the unmanaged environment, memory is addressed at the byte level, so you'll have to create functions to look up half-bytes. It's going to be a lot of work. – VoteCoffee Feb 06 '17 at 19:33
  • So creating that 4b var, it makes all the work for nothing for the cost that have using it? – driconmax Feb 06 '17 at 19:35
  • A managed environment like c# doesn't let you control memory allocation at a low level. Also, for every variable you allocate, it add padding data required for garbage collection. Managed code decouples you from control of memory, threading, etc. – VoteCoffee Feb 06 '17 at 19:40
  • There's no code you could write in a managed environment to accomplish what you want. If you wrote a helped application in unmanaged code like c++ and marshalled your work over to it and let it handle the memory and work performed on the memory, you could do it. It would be a lot of work though. Better to just write the code in C++ to begin with. – VoteCoffee Feb 06 '17 at 19:42
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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.

Brandon
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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

Uladzimir Palekh
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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.

sunside
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