On Fri, 18 Jul 2008, stefan kersten wrote:
On 17.07.2008, at 21:46, Lennart Augustsson wrote:
If scaleFloat and exponent are implemented with bit twiddling
they can
be quite fast.
is there a way in ghc to 'cast' between float/int32 and double/
int64 (without going through memory)?
I read this as
"Is there any way to take a 32-bit float in a register and end up
with a 32-bit int
in a register, without going through memory, in GHC?
How about the other way around?
How about 64-bit floats and integers?"
It is rather hard to do portably in GHC what some hardware does not do.
A long time ago hardware architects decided that separating the
integer and
floating point register files was a Good Thing.
The machine I know best is SPARC, where there are no instructions to
move
data directly between integer registers and floating point registers.
On the other hand, there are other pressures, notably graphics.
While integer and floating point registers may be kept separate, there
are often
"vector" instructions that let you operate on integers in the floating-
point
registers. (Such as the VIS instructions on SPARCs, which are
technically
optional.) Exploiting such instructions tends to be rather non-
portable.
All things considered, I wouldn't worry about it too much: the memory
in
question should be at the top of the stack, so should be in L1 cache,
so should
be pretty fast to access, and other things may be more significant.
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