the algorithm of decimal<->binary conversion

[Michael Mair]

Re: the algorithm of decimal&lt;-&gt;binary conversion



Mars wrote:[color=blue]
> Peter Nilsson mentioned:
>[color=green]
>> Peter Nilsson wrote:
>>[/color]
>
> And what's that "1u" mean in your program??
>
> e.g.
> q2=(1u<<(q4-1)<<1)-1;[/color]

You were not there when they were talking about constants...

1 (int)
1u, 1U (unsigned int)
1l, 1L (long)
1UL, 1ul, 1LU, 1lu ....
1.0 (double)
1.0F,1.0f (float)
1.0L,1.0l (long double)


-Michael
--
E-Mail: Mine is a gmx dot de address.

[Chris Williams]

Re: the algorithm of decimal&lt;-&gt;binary conversion

Flash Gordon wrote:[color=blue]
> Chris Williams wrote:[color=green]
> > 2 >> 1 = 1 //division by two
> > 4 >> 1 = 2
> > 6 >> 1 = 3
> > 8 >> 1 = 4
> > 8 >> 2 = 2 //division by four
> >
> > 1 & 1 = 1 //modulus of 2
> > 2 & 1 = 0
> > 3 & 1 = 1
> > 4 & 1 = 0
> > 4 & 2 = 0 //modulus of 4[/color]
>
> Any decent optimising compiler will do this optimisation when dealing[/color]
[color=blue]
> with division by a constant. So it is generally better to write what[/color]
you[color=blue]
> mean rather than making the code harder to read.[/color]

True. It's a two second test, but indeed there might be no change if
your compiler was spitting your code out using shifts and ands in
secret.

Though I was never big on trusting the compiler to do anything past
predetermining all math between constants--e.g. time = y + 1000 * 60;
-> time = y + 60000; Just the general idea that between knowing how to
do it myself or having the best optimizing compiler, I'd rather know
what I'm doing. Though I would want one for any large project to deal
with the 99% of code that won't be used intensively.

-Chris