> (But it could be a problem if the buffer is
> right at the end of the virtual memory space . Sorry about the buggy ...

that will be a problem if the hardware is sloppy, but it would be true regardless how
you wrote the test (because it's the resulting prefetch addresses that then matter).
i think hardware designers now know about this problem (since it's fairly old)
but that probably hasn't stopped a few from not including it in the processor manual
but slipping it instead into the errata.