Hello,

I'm working on KerGIS, a BSD licenced revival of CERL GRASS, in order to
make it compile and run on Plan 9 too---at the moment, it compiles and
runs on any POSIX Unix flavour.

Even if a huge amount of work has already been done for cleaning,
reorganizing and extending the original sources, confrontation with Plan
9 shows that it is far from being, if not ideal, even sensible in some
area.

The first step---for Plan 9---will be a compilation using APE, and the
development of a graphical visualization using Plan 9 libdraw.

But I need too, for Plan 9 and others, to isolate correctly arithmetic
operations (I include not only integers but floats too in this
expression) in order to identify correctly the domain of definition of
the algorithms.

AFAIK, ISO C for examples does not mandate anything about integer
overflows (may silently wraps). C99 has added some support for IEEE754,
but the handling of "exceptions"---that may or may not be faults---is
still fuzzy for me.

[I forgot the references]:

On Wed, Jul 25, 2007 at 05:51:55PM +0200, tlaronde wrote:

MMIX is the mythical RISC machine described by Donald E. Knuth in:

1 The Art of Computer Programming, Volume 1, Fascicle 1: MMIX, A RISC
Computer for the New Millenium, Addison-Wesley, 2005.

and

2 MMIXware, A RISC Computer for the Third Millennium, Springer, Lecture
Notes in Computer Science n°1750, 1999.

i may not be qualified to answer all those questions for you, but i'll
try my best. i was dealing with FP exceptions last week and
consequently may have some of the answers:

i don't think there's anything about integers, but float exception
behaviour can be controlled via the getfcr/setfcr routines described
in getfcr(2). that man page will also tell you how to figure out
whether a particular machine supports those.

in my particular case the code I was porting defined NaN as a constant
and threw an exception whenever it ran. one particular quirk that i
observed was that an exception was thrown regardless of whether I
defined a silent or a non-silent NaN... my "solution" was simply to
turn off FPINVAL via setfcr(). if you're porting via ape, as i was
doing, the best solution is to get the little bits of assembly that
constitute the *fcr routines, compile them with 8a and link them
against the

On Wed, Jul 25, 2007 at 10:25:28AM -0600, andrey mirtchovski wrote:

Yes, definitively. Thank you very much!

It's almost clear that I need for KerGIS to orthogonalize things, so
that in the libgis are indeed system dependant (POSIX or Plan 9)
facilities and only these, and in a libarithm sys dep and machine
dependant arithmetic.

All the rest should be userland computation and almost usable as
is---minus the idiosynchrasies about C and libc [headers].

Thanks once more,

On Wed, Jul 25, 2007 at 10:25:28AM -0600, andrey mirtchovski wrote:

Perhaps a hint on this. In The Intel documentation (Intel64 and IA32
Architectures Software Developer's Manual, Volume 1, §4.8.3.4):

------quote
SNaNs are typically used to trap or invoke an exception handler.
They must be inserted by software; that is, the processor never
generates an SNaN as a result of a loating-point operation.
------endquote