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- Subject: Re: bug in ceillog2 macro (Lua-5.1.4)
- From: Roberto Ierusalimschy <roberto@...>
- Date: Fri, 7 Jan 2011 13:44:32 -0200
> Hi List,
> In Lua-5.1.4 macro
> #define ceillog2(x) (luaO_log2((x)-1) + 1)
> gives wrong answer when x is 0.
> ceillog2(0) => 32 (should be 1).
> I attached below a standalone code snippet to demonstrate the problem.
> I use Lua-5.1.4 on Ubuntu-9.04 x86 (32 bits).
> There are several ways to fix it and I like _none_ of them.
> (1) Ignore the bug. Just make sure that x>0 always.
This is an internal function; it is not for general use. It cannot be
called with a zero argument (see the calling points). It should not be
called with a zero argument, because math.ceil(math.log(0, 2)) is -inf
Where is the bug?