Re: Floating point load-store behaviour.
- From: "Ancient_Hacker" <grg2@xxxxxxxxxxx>
- Date: 23 Aug 2006 12:46:27 -0700
thisismyidentity@xxxxxxxxx wrote:
Hi all,
I am trying to predict the behaviour of floating point load and store
operations on integer locations. I ve written a small piece of code
having some inline assembly code which I am describing here.
Not a good subejct foer this group, which is tightly limited to pure C
discussions.
But
The FPU hardware in 99.73% of all computers ever made has absolutely no
idea that an area of memory has had "integers" stored into it. There
were a few Intel aipx432 prototype chips made with type checking in
hardware, but they're hard to find nowdays.
If you load a floating-point register from memory, I suspect the FP
hardware has the freedom to fudge the bits any way it feels like, as
long as the operation doesnt change the FP value of the number.
For example, if you load up a denormalized number, the FP unit may
normalize the number it picks up. It still will have the exactly same
value, as a FP number, but of course if it's an integer it will be all
messed up.
BTW the register-oriented fp move instructions don't mess with the
bits, ever. That allows them to be used to move or hold integer or
packed MMX operands without danger of lossage.
.
- References:
- Floating point load-store behaviour.
- From: thisismyidentity
- Floating point load-store behaviour.
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