From: Brent Roman <brent@...>
Date: 2008-12-06T10:17:52+09:00
Subject: [ruby-core:20396] Re: Leave my open classes alone (was   Behavior: autoload calls rb_require()  directly)


Paul,

I understand your concern, but it may not be an tricky as you believe.

I think the MagLev folks addressed this by truncating 
the binary exponent to 8 bits in their immediate object format while 
always preserving the full mantissa.  There should thus be no loss of
precision,
but there will be a loss of dynamic range.  Those few floats
whose absolute value is greater than approx. 2**127 (1.0e+38) could not be
represented as SmallFloats, so they would be automatically promoted to
non-immediate
Float objects, much like 2**30 gets silently promoted to a Bignum in 32-bit
MRI today.

- brent


Paul Brannan wrote:
> 
> On Sat, Dec 06, 2008 at 04:46:36AM +0900, Brent Roman wrote:
> 
> You can't easily do these sorts of tricks with floating point numbers;
> it breaks IEEE floating point compatibility.  On some platforms you
> might be able to get away with breaking out the exponent and dropping a
> few bits off it, but you'd want a LOT of unit tests to ensure you don't
> introduce a subtle incompatibility.
> 
> Floating point code can be very fragile, and I'd feel much better about
> a solution that leaves the floating point number intact.
> 
> Paul
> 
> 
> 
> 

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