Power of 2

[Ryan Binns]

:laugh:!

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

[Divyang Mithaiwala]

Hello v2.0, We are on visual C++ & my suggesion is not wrong for it.

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Divyang Mithaiwala System Engineer & Software Developer

[toxcct]

Divyang Mithaiwala wrote:

my suggesion is not wrong for it.

yes it is, it will not work on a MFC/Win32 project... it is only for managed C++ (which is not for this forum, but for the C++/CLI forum instead)

[RichardS]

Hi Ryan, Thanks for the help. The code is great and the application is for an embedded -> PC interface. cheers Rich "Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far the Universe is winning." -- Rich Cook

[RichardS]

Hi Ryan, Is there is quick way for now making x a power of 2 after you have decided that it is not? regards, Rich "Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far the Universe is winning." -- Rich Cook

[Stephen Hewitt]

Modified version is still wrong - It will treat any integer as a power of 2. Steve

[toxcct]

i did not pretend to modified my post for a much working stuff...

[David Crow]

#define ISPOWER2(x) (!((x)&((x)-1)))

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"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

[David Crow]

_Russell_ wrote:

This function that I wrote last year find the bigger long, greater than the input value, that is a power of 2.

Why not just use log2()?

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"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

[Ryan Binns]

RichardS wrote:

Is there is quick way for now making x a power of 2 after you have decided that it is not?

Not that I know of. I've never had to do this. Would you round up or down?

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

[RichardS]

Round up. So far I have a loop (for 32-bits) shifting 0x80000000 down until the & with x is successful, then shifting it back up by one. regards, Rich "Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far the Universe is winning." -- Rich Cook

[Russell]

Because my function is faster (I think) than log2(). But if I'm wrong let me know how have a faster function. And why. thanks

Have a nice code day ;)

[David Crow]

_Russell_ wrote:

...let me know how have a faster function.

This one benchmarks faster than the one you've shown:

unsigned long Next2Power(unsigned long x)
{
x--;
x |= x >> 1;
x |= x >> 2;
x |= x >> 4;
x |= x >> 8;
x |= x >> 16;
x++;

return x;

}

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"Let us be thankful for the fools. But for them the rest of us could not succeed." - Mark Twain

"There is no death, only a change of worlds." - Native American Proverb

[cmk]

#define CK_ISPOW2(n) ( ((n)&((n)-1)) == 0 )

ullong FkGrainDn2( ullong S, ullong G )
{
// if( !CK_ISPOW2(G) ) return( FkGrainDnN(S, G) );
S = S & ~(G-1);
return(S);
}

ullong FkGrainUp2( ullong S, ullong G )
{
// if( !CK_ISPOW2(G) ) return( FkGrainUpN(S, G) );
G -= 1;
S = (S+G) & ~G;
return(S);
}

where: S is value to round G is a power of 2 ...cmk Save the whales - collect the whole set