Re: [PATCH] PPC assembly implementation of SHA1

On Sat, 2005-04-23 at 12:42 +0000, linux@horizon.com wrote:

- You don't need to decrement %r1 before saving registers.
  The PPC calling convention defines a "red zone" below the
  current stack pointer that is guaranteed never to be touched
  by signal handlers or the like.  This is specifically for
  leaf procedure optimization, and is at least 224 bytes.

On ELF ppc32 ABI ? Hrm... the SysV ABI document says

"The only permitted references with negative offsets from the stack
pointer are those described here for establishing a stack frame."

I know MacOS had a red zone, but do we ?

- Is that many stw/lwz instructions faster than stmw/lmw?
  The latter is at least more cahce-friendly.

More cache friendly ? Hrm.. I wouldn't be sure. Also, I remember readind
a while ago that those store/load multiple instructions aren't that
recommended. They aren't very good on some CPU models. I would expect
the bus/cache bandwidth to be the limiting factor here anyway, and as
you point out below, the they don't deal with unaligned access very well
in all cases.