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digitalmars.D.learn - next power of 2

reply "ref2401" <refactor24 gmail.com> writes:
is there any Phobos function to calculate the next power of 2 of 
the specified number?
Oct 06 2012
next sibling parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 10/6/12 4:48 PM, ref2401 wrote:

 is there any Phobos function to calculate the next power of 2 of the
 specified number?


Use 1U << bsr(x).

http://dlang.org/phobos/core_bitop.html#bsr


Andrei
Oct 06 2012
prev sibling next sibling parent reply Dmitry Olshansky <dmitry.olsh gmail.com> writes:
On 07-Oct-12 00:48, ref2401 wrote:

 is there any Phobos function to calculate the next power of 2 of the
 specified number?


No though it's reinvented in a couple of places I think.

Anyway this should work for unsigned numbers:

import core.bitop;
T nextPow2(T)(T x){
	return x == 0 ? 1 : 1^^(bsr(x)+1);
}

-- 
Dmitry Olshansky
Oct 06 2012
next sibling parent reply Dmitry Olshansky <dmitry.olsh gmail.com> writes:
On 07-Oct-12 00:54, Dmitry Olshansky wrote:

 On 07-Oct-12 00:48, ref2401 wrote:

 is there any Phobos function to calculate the next power of 2 of the
 specified number?


 No though it's reinvented in a couple of places I think.

 Anyway this should work for unsigned numbers:

 import core.bitop;
 T nextPow2(T)(T x){
      return x == 0 ? 1 : 1^^(bsr(x)+1);
 }


Yikes, 1<<(bsr(x)+1) or 2 ^^ (bsr(x)+1) ...
still haven't got used to 2^^x notation compared to shifts.


-- 
Dmitry Olshansky
Oct 06 2012
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 10/6/12 4:57 PM, Dmitry Olshansky wrote:

 On 07-Oct-12 00:54, Dmitry Olshansky wrote:

 On 07-Oct-12 00:48, ref2401 wrote:

 is there any Phobos function to calculate the next power of 2 of the
 specified number?


 No though it's reinvented in a couple of places I think.

 Anyway this should work for unsigned numbers:

 import core.bitop;
 T nextPow2(T)(T x){
 return x == 0 ? 1 : 1^^(bsr(x)+1);
 }


 Yikes, 1<<(bsr(x)+1) or 2 ^^ (bsr(x)+1) ...
 still haven't got used to 2^^x notation compared to shifts.


That's right, apologies for my buggy suggestion and my suggestion of a 
buggy suggestion :o).

Andrei
Oct 06 2012
parent Dmitry Olshansky <dmitry.olsh gmail.com> writes:
On 07-Oct-12 00:58, Andrei Alexandrescu wrote:

 On 10/6/12 4:57 PM, Dmitry Olshansky wrote:

 On 07-Oct-12 00:54, Dmitry Olshansky wrote:

 On 07-Oct-12 00:48, ref2401 wrote:

 is there any Phobos function to calculate the next power of 2 of the
 specified number?


 No though it's reinvented in a couple of places I think.

 Anyway this should work for unsigned numbers:

 import core.bitop;
 T nextPow2(T)(T x){
 return x == 0 ? 1 : 1^^(bsr(x)+1);
 }


 Yikes, 1<<(bsr(x)+1) or 2 ^^ (bsr(x)+1) ...
 still haven't got used to 2^^x notation compared to shifts.


 That's right, apologies for my buggy suggestion and my suggestion of a
 buggy suggestion :o).


Post of the day :)

-- 
Dmitry Olshansky
Oct 06 2012
prev sibling parent Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 10/6/12 4:54 PM, Dmitry Olshansky wrote:

 On 07-Oct-12 00:48, ref2401 wrote:

 is there any Phobos function to calculate the next power of 2 of the
 specified number?


 No though it's reinvented in a couple of places I think.

 Anyway this should work for unsigned numbers:

 import core.bitop;
 T nextPow2(T)(T x){
 return x == 0 ? 1 : 1^^(bsr(x)+1);
 }


That's right, apologies for my buggy suggestion.

Andrei
Oct 06 2012
prev sibling parent "bearophile" <bearophileHUGS lycos.com> writes:
On Saturday, 6 October 2012 at 21:00:57 UTC, ref2401 wrote:

 is there any Phobos function to calculate the next power of 2 
 of the specified number?


See:
http://d.puremagic.com/issues/show_bug.cgi?id=6343

Bye,
bearophile
Oct 06 2012