Re: bug in ceillog2 macro (Lua-5.1.4)
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- Subject: Re: bug in ceillog2 macro (Lua-5.1.4)
- From: Leo Razoumov <slonik.az@...>
- Date: Fri, 7 Jan 2011 10:09:17 -0500
On Fri, Jan 7, 2011 at 09:57, liam mail <liam.list@googlemail.com> wrote:
>
> Unless my maths fails me isn't log2(0) infinity or undefined?
> Liam
>
Mathematically, log2(0) is negative infinity. But here we talk about
ceillog2 function which is a ceiling by nearest power of two. Also
luaO_log2(x) implementation via shifts and integer table lookups makes
it mathematically quite different from, real log2 function.
For any non-negative integer x minimal number of bits to store x is
ceillog2(x)+1. And this is the practical meaning of ceillog2 in Lua
context.
--Leo--