[kaffe] HAVE_move_float_const

Dalibor Topic robilad at yahoo.com
Tue Jul 1 04:05:01 PDT 2003

Ciao Gerlando,

--- Gerlando Falauto <iurly at writeme.com> wrote:

> Nope, it's perfectly clear but still I don't get your point. If you wanna
> be safe, shouldn't you just be CONSISTENT? Declare it as a float, and let
> the compiler decide what casts are appropriate. At this level, so long as
> I get what was meant to be passed (which is a *float*), I shouldn't really
> care what the compiler does. The point here is, I want a float constant

Different versions of C 'standards' (and thus different versions of compilers)
have had different interpretations of what you really meant to be passed when
you wrote 'float'. :)

for another nice explanation of the pitfalls involved.

> (which is 32-bit wide) exactly as it was written in the classfile, so I
> can move it to a register (as a 32-bit chunk). If the compiler wants to
> promote it as an internal optimization, that is none of my business!

The C99 standard doesn't guarantee you'll have 32 bit wide floats. It doesn't
even guarantee the floats will be 'base 2'. But fortunately, kaffe hasn't been
ported to such a beast yet, AFAIK ;) 

On the other hand, we're talking about the jitter here, right? Then you of
course you know more about types and their representations in the hardware.

> If I get it as a double, I have to cast it back to a float. Apart from
> the waste of time, is that guaranteed to be non-destructive?

I don't think it's guaranteed to be non-destructive. NANs for example may not
get to be the same NANs they were before...

But anyway, if just using floats works for you, please port a patch and let
others evaluate it. That's much easier than trying to interpret the C standard

dalibor topic

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