C#•2y ago

❔ How Would I extract a single byte from an int

In my project, I have information which is effectively a byte[4] stored in an int32, I want to grab a specific byte from this I currently have the code

byte adjacentTileType = _tiledata >> (i * 8);

byte adjacentTileType = _tiledata >> (i * 8);

this produces an error as it should, but how would I do this properly

16 Replies

Sherbert LemonOP•2y ago

just realised after sending that I could left shift it before right shifting it, so that all other values are overflown and elimenated is that the best way? or is there a better?

byte adjacentTileType = (byte)((_tiledata << ((i - 3) * 8)) >> (3 * 8));

byte adjacentTileType = (byte)((_tiledata << ((i - 3) * 8)) >> (3 * 8));

is what I have changed it to, but it seems a bit verbose with too many brackets also is "bitfucking" a word which people use? I have been using it a bunch with my friend when we are clueless about bit shifting, but I googled it and couldn't find anyone else using it, have we made it up? it is the verb form of "bitfuckery"

Jester•2y ago

there are a few ways you could do this

Jester•2y ago

int i = ...
byte a = i & byte.MaxValue;
byte b = (i >> 8) & byte.MaxValue;
etc. or
unsafe {
byte* p = &i;
byte a = p[0];
byte b = p[1];
etc
}

int i = ...
byte a = i & byte.MaxValue;
byte b = (i >> 8) & byte.MaxValue;
etc. or
unsafe {
byte* p = &i;
byte a = p[0];
byte b = p[1];
etc
}

or with this class but then you are allocating memory which is maybe not prefered https://learn.microsoft.com/en-us/dotnet/api/system.bitconverter.getbytes?view=net-7.0#system-bitconverter-getbytes(system-int32)

BitConverter.GetBytes Method (System)

Converts the specified data to an array of bytes.

Jester•2y ago

more complicated bitfuckery https://graphics.stanford.edu/~seander/bithacks.html @Sherbert Lemon does this help?

Sherbert LemonOP•2y ago

does the first one work? how does it just work with an and? but yeah defo not the getbytes, the whole point of the bitfuckery was to avoid a few hundred to a few thousand arrays needlessly oh yeah ok i get it now i'm not very good at bitfuckery, i partially did this to get better at it

Jester•2y ago

the & byte.MaxValue is so only the 8 bits stay and the other turn 0

Sherbert LemonOP•2y ago

yep that is quite a nice concise way of doing it thanks how does the pointer one work then, I will defo just use the first thing but that intrigues me

Jester•2y ago

with pointers you can change the type of a thing (which is dangerous to do ofc) so if the compiler thinks it points to a byte array instead of an int. an int is 4 bytes so you can use it like its a byte array of 4 bytes instead

Sherbert LemonOP•2y ago

ah ok that is nice, not a very c# way of doing it tho lol, and this is in unity so it is a bit of a pain to enable unsafe code thanks though, I will defo have a read through the bitfuckery page, he calls it bittwiddling, is that the more normal way of calling it?

Jester•2y ago

idk

Sherbert LemonOP•2y ago

what do you call it?

Jester•2y ago

id call it bitfuckery

Jester•2y ago

dont do this pointerfuck though omegalul

(i just want to show it bcuz i think its a bit crazy)

Jester•2y ago

pointers are dangerous so yeah go with the safe solution

Sherbert LemonOP•2y ago

lol what, that took me a good minute to clock what it was doing, weird ig you have to pin it but is a bit of a pain to do, i'll leave pointerfuckery to cpp that is good though, I can blame you if I ever call it bitfuckery in class and say that is what everyone calls it. At least whenever we finally get to that topic lol, the computer science curriculum moves so slowly in the uk

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ How Would I extract a single byte from an int