Re: Re: NaN packing for TValue

[Tony Finch <dot@...>]

On Fri, 25 Feb 2011, Peter Cawley wrote:
> 2011/2/24 Yura Sokolov <funny.falcon@gmail.com>:
> > Well, x64 at the moment uses only 48 bits for addresses.
> >
> > 1bit for a sign + 11bits for mantis + 1bit for quiet NaN + 48 bits for an
> > address = 61bit

You mean 11 bits for the exponent :-)

> > So that there is 3bits for tagging.
> >
> > Currently Lua uses 13 different tag values, so that it would be tricky to
> > pack them into three bits :)
>
> If you're willing to pay the price of an extra indirection, you might
> be able to get away with using a single tag value for all GC types, as
> the GC header stores the tag value.

Or steal another three bits from the bottom of the pointer...

Tony.
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