On 23 Sep 2009, at 8:11 pm, Shiro Kawai wrote:

> An interesting approach is taken by a Ruby implementor
> (Koichi Sasada): Taking one tag bit from exponent (instead of
> mantissa) of IEEE double floats. [...]

Awesome trick! I'd really love:

a) to collect all such clever tricks, and write them up somewhere, as
they seem to be very widely distributed and hard to find

b) CPU manufacturers to add custom hardware to make life hard for
dynamic languages (such as, a single instruction that adds two
immediate numbers, using tag bits to tell if they're floats or
fixnums, or calling a handler if they're Something Else)... more and
more code these days comes from such languages, so it'd surely be
worth it in the long run. But the long run isn't always what's in the
best interests of hardware companies...

--
Alaric Snell-Pym
Work: http://www.snell-systems.co.uk/
Play: http://www.snell-pym.org.uk/alaric/
Blog: http://www.snell-pym.org.uk/archives/author/alaric/




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