On 09/06/2011 08:44 PM, austin seipp wrote:
On Thu, Jun 9, 2011 at 1:53 PM, Andrew Coppin
<andrewcop...@btinternet.com> wrote:
I'm still left wondering if using 32-bit instructions to manipulate 64-bit
values is actually that much slower.
The problem is you're probably going to need to spill things
(somewhere) in order to operate on the upper 32bits of any given
register in the non trivial case. x86 already is pathetic in its 8 GP
registers. amd64 brings it up to 16.
Well, that's true enough.
Given that AMD64 adds more registers, I'm surprised that this apparently
makes such a small difference to wall-clock run-times. (But perhaps it
makes a bigger difference for GHC. I don't know.)
I'm wondering if you could write the operations you want is small C stub
functions, and FFI to them and do it that way. I don't really know enough
about this sort of thing to know whether that'll work...
It's highly unlikely that the cost of a foreign call (even an unsafe
one) in terms of just CPU cycles will be cheaper than executing a few
primitive arithmetic ops on the CPU.
Yeah, you're probably right there actually.
Too bad GHC doesn't support inline assembly yet... (Or does it? I know
it supports inline Core now.)
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