Re: Boolean Variable Type
On Thu, 17 Feb 2000, Brian Broker wrote:
> On Thu, 17 Feb 2000 21:21:54 GMT, Lewis Townsend wrote:
>
> >But I don't really care if it
> >takes up 32 bytes of space or not.
>
> I think would really concern me if it took up 32 bytes of space... unless
> you meant to say 32 bits (4 bytes). 8^)
>
> But I'd have to agree that the memory 'wasted' on storing flags in an
> integer is trivial these days. And I would bet that there would be a
> performance hit from the need to (internally) mask a bit to determine a
> boolean value.
>
> -- Brian
>
You'd better believe it. The minimum a CPU can write to memory is
8 bits. Most C programs use 32-bit integers for flags. They should be
using 8-bit ints, but rarely do. The problem with a data type of only one
bit is that it takes far more to address it than it contains. Furthermore,
the only thing you can put in those remaining seven bits are other 1 bit
types.
If you've only got 1 flag in your programn, a boolean type will
save you no memory (it will actually waste some, address & bit vs.
address). 32 bits will address (by byte) 4,294,967,296 bytes. To do this
by bit, you need 35 bits, three bits wasted per address. Then there's the
overhead involved in translating the address into a readable form, and
back. Generally, there's no real advantage.
To demonstrate this, think about writing flag handling routines in
euphoria. You'll notice that no matter how you do it, it will waste both
memory and speed. Same deal if it were compiled into the language.
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