On Thu, Jan 16, 2014 at 1:12 PM, Jens Nockert <j...@nockert.se> wrote: > > On 2014/01/16, at 17:40, Jason Orendorff <jason.orendo...@gmail.com> > wrote: > > Or maybe: flip the function around so that it returns the number of > > bits in the binary expansion of the value: Math.bitlen(15) === 4. This > > is just (32 - CLZ), so it effectively computes the same thing as clz. > > The advantage is that it extends naturally to integers of any size. > > What is Math.bitlen(-1) then? Isn’t this just the same problem as before, > except it happens for negative numbers instead of positive?
FWIW: Common Lisp has rigorously transparent (that is, you cannot observe the machine word size) bigints and quite a few binary operations defined on them, so it's where I personally would look for precedent on such questions. It doesn't have clz or bitlen per se, but it has these two functions which contain positions on the issue: integer-length http://www.lispworks.com/documentation/HyperSpec/Body/f_intege.htm Returns the number of bits needed to represent 'integer' in binary two's-complement format. [Comment: This is equivalent to bitlen + 1 in order to count the sign bit, and is well-defined for negative numbers.] logcount http://www.lispworks.com/documentation/HyperSpec/Body/f_logcou.htm Computes and returns the number of bits in the two's-complement binary representation of 'integer' that are `on' or `set'. If 'integer' is negative, the 0 bits are counted; otherwise, the 1 bits are counted. (If I had guessed without actually reading the docs, though, I would have had logcount rejecting negative numbers.)
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