On 2013-11-26 21:31:55 +0000, bioinfornatics said:
On Tuesday, 26 November 2013 at 21:18:29 UTC, Shammah Chancellor wrote:
On 2013-11-26 21:00:56 +0000, bioinfornatics said:
On Tuesday, 26 November 2013 at 20:50:13 UTC, bioinfornatics wrote:
On Tuesday, 26 November 2013 at 20:29:00 UTC, bearophile wrote:
bioinfornatics:
I wrote some template to compute at compile time how many bits is need
for a number x. http://www.dpaste.dzfl.pl/99a842fd
That works for small number but after i got an error about limit recursion
Instead of template recursion, have you tried regular code run at compile time?
http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious
Bye,
bearophile
Thanks i will take a look
this one seem to be interesting
http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogLookup
is like i do but use a table than me i used a recursive way. I go to try it :-)
I think you just have a bug in your template code not terminating. At
most you should execute 4 times. I think there's a problem with
casting down from byte to bool.
However, not user if LesserType is what you're after, but this works:
template log2(ulong x)
{
static if( x >> 8 )
{
enum log2 = log2!(x >> 8) + 8;
}
else static if( x >> 1)
{
enum log2 = log2!(x>>1) + 1;
} else
{
enum log2 = 1;
}
}
Thanks your way is much easier to write, works fine :-)
I would suggest turning it into a compile-time-function though as this
will instantiate a large number of templates if you use is
repetitively. Remember that templates are cached by DMD.
int log2(const ulong x)
{
if( x >> 8 )
{
return log2(x >> 8) + 8;
}
else if( x >> 1)
{
return log2(x>>1) + 1;
} else
{
return 1;
}
}
void main()
{
pragma(msg, log2(1UL<<63));
}
