How to manipulate specific bits of a variable

[User137]

//edit: I wrote (but didn't test) function that would check if specific bit is set. You'll need math unit for that one:

function IsBitSet(num:integer;bit:byte):Boolean
var bitnum:Integer;
begin
  bitnum:= Trunc(intpower(2,bit);
  Result:= (num and bitnum) = bitnum;
end;

Though it should work fine.

Dan already gave more optimized code for that

function GetBit(const Value, Bit: LongWord): Boolean;
begin
  Result := Boolean((Value shr Bit) and 1);
end;

Both trunc() and intpower() do a massive amount of extra work.

[Darkhog]

I guess it should work fine too. But why using longword for bit no.? Byte would do here much better and I don't suppose we'll need to check like 5000th bit of value soon. Therefore longword would just waste memory while byte would be much more memory-efficient here, especially when dealing with embedded systems.

[imcold]

Byte would be worse actually - more generated code. And you wouldn't save any memory, as it would be most likely passed in a register or pushed as a 4B value on the stack, depending on ABI.