Rumour about IBM benchmarks

[jim frost]

mherman at alias.UUCP (Michael Herman) writes:
>Although I am less familiar with them, there are supposedly a number of
>C library (i.e. zero terminated) string functions what have also been
>implemented directly in the silicon.

Sort of.  There are a number of operations which act on multiple
sequential registers which presumably contain a string.  It's fast and
easy to load a bunch of registers with a bunch of sequential bytes,
act on them in the registers (often with instructions that work across
sequential registers) then write back the bytes.  Not exactly C string
handling in silicon but it's not a lot of work to implement the C
functions and they'll have good performance.

XLC generates some interesting code when dealing with structures that
uses the string load and store instructions.  Even more interesting is
that it often doesn't use the string instructions when it could (eg
when saving the argument registers to the stack in a varargs
function).

Happy hacking,

jim frost
saber software
jimf at saber.com