[SM-Discuss] Smallest Source Mage
charkins at upl.cs.wisc.edu
Sun Jul 28 17:13:39 EDT 2002
> > > - Even if the iso is compiled with pentium "instructions" it should be
> > > usable on any x86 compatible cpu... should'nt it ?
> > No. Each new family of CPUs introduce new instructions that weren't
> > present in older familys. If you compile binaries using these
> > instructions, and then try to run them on a system with a lower class
> > CPU, they will fail. Very few instructions were added between the 486
> > and the origial pentium though, which is probably why the ISO binaries
> > are runnable on a 486. Cast nasm and read it's docs for a (much) more
> > detailed reference on the x86 instruction set and which are available on
> > which family.
> Fine... I'm a bit surprised here, since I tought that this kind of things
> should not happen.
If this weren't the case, the architecture selection and subsequent
optimizations in sorcery (at least CPU dependent ones) would not be
possible. IIRC, the first major additions to the IA32 instruction set came
with the Pentium w/MMX. These added new MMX instructions which allowed
(among other things) better use of the processor ALU's for doing smaller
math operations. Instead of adding bytes one at a time using 32bit math,
why not do four at a time by splitting up the ALU.
The bottom line is that they do maintain backwards compatability, but
have added instructions to make better use of the processor for certain
types of applications. The MMX instructions are mostly centered around
doing faster arithmetic for audio/video apps. Compilers can then make use
of these extra instructions automatically.
I think these things *should* happen!
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