Re: how to specify power of number

Antoninus Twink <nospam@xxxxxxxxxxxxxx> wrote in
news:slrng0h483.166.nospam@xxxxxxxxxxxxxx:

On 18 Apr 2008 at 11:01, Bartc wrote:
You would have to use pow(256,3) which uses floating point arithmetic
-- not recommended, even though the compiler is likely to optimise.

Your code is fine as it is, the compiler will optimise 256*256*256 to
*16777216 or <<24. Or just write those in yourself.

For general integer powers, a simple square-and-multiply algorithm is
a good bet, e.g.

unsigned long long power(unsigned a, unsigned b)
{
unsigned long long r, bit, pow;
for(bit=r=1, pow=a; bit<=b; bit<<=1, pow *= pow)
if(b & bit)
r*=pow;
return r;
}

The hardest part is checking for overflow - left as an exercise for
the reader...


Thank you both. I must admit, that the code Is almost a mystery for me :-)
.

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