Re: [ANN] Lua 5.2.0 (rc7) now available

[KHMan <keinhong@...>]

On 12/10/2011 12:20 AM, Roberto Ierusalimschy wrote:
> > and the simple tests:
> >
> > >   print(2^3 - 8)
> > -1.7763568394003e-015
> > >   print(3^4 - 81)
> > 2.8421709430404e-014
> > > =2^4-16
> > -1.7763568394003e-015
>
> These all should be zero. It really seems that the 'pow' function
> from the C library is broken.

Correction to my previous post, usage of 2 ** (y log2(x)) for x86 
may not be the real reason. For one, the value I got 
(-2.84217e-014) had the wrong sign, and secondly, for 2^3-8, the 
calculation is exact.

FWIW, for the result -2.84217e-014, the IEEE754 double byte value 
of the 81-something value versus the normally expected result is:

0x40543FFFFFFFFFFF => short of -2.84217e-014
0x4054400000000000 => 81 exact

so Tymur's result should be off by 1 in the other direction,
0x4054400000000001

Sorry for the noise. But a non-exact value for 2^3-8 seems pretty 
bad for business, though...

--
Cheers,
Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia