On Fri, Apr 01, 2016 at 06:23:28PM +0100, Andy Bennett wrote: > Thanks Peter! > > I'm mostly using log2 to work out if numbers are a power of two and find > the highest bit that they have set. > > Is there a more robust way to do that in CHICKEN when using the numbers > egg and bignums?
It's probably better to do something like this: (= (arithmetic-shift 1 (sub1 (integer-length x))) x) If you find it clearer, you can also use (= (expt 2 (sub1 (integer-length x))) x) Note that the former accepts zero as a power of two, while the latter doesn't. And if you want to have some fun with bits: (zero? (bitwise-xor (arithmetic-shift 1 (sub1 (integer-length x))) x)) Maybe we should consider including "first-bit-set" or "logcount" from SRFI-60, what do you think? These would allow us to avoid constructing potential bignums just to check the lowest bit. I initially decided against including SRFI-60 because it's such a huge grab-bag of procedures without much of a design behind it, and the worst part is that most of them have two names instead of one :( Cheers, Peter
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