Mail Archives: djgpp/1999/07/12/10:17:45
Michal wrote:
> > >If you take 2 to the 4th power witch is 16, you can say:
> > > ch-=16;
> > >and that will turn of the 4th bit if it is on. If it is off and you want
> it on
> > >you can go
> > > ch+=16;
> > >so basicly you add or subtract 2 to the power of the bit you want.
> >
> > or, if you like assembler you can use "setb" and friends.
> > in addition, OR'ing allows you to set a bit, and you can also AND a bit out
> > with a mask. using logical bitwise operations are usually faster than
> > adding and subtracting.
> Not true, i don't know about other processors but pentium and higher
> (which is the platform of djgpp) execute them all at the same speed,
> which is in perfect conditions two instructions per clock on pentium and
> pentium MMX and two or one (depending on operands types) instruction for
> pentium pro and pentium II, also in both you can use registers or
> immediate so there are no speed differences.
But, it is much safer to use the bit-wise logical operators. Adding 16 to a
number with the 5th bit already set will mess things up.
--
-Rolf Campbell (39)3-6318
- Raw text -