Bruno, why is the index argument to array_displace_check
uintL and unitV?
is this a bug?
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Array dimensions are stored as an uintL.
array-dimension-limit = 2^32-1.
Therefore all array indices and sizes are 32-bit.
Care must be used only when a Lisp integer is used as an
to avoid _implicit_ uintV -> uintL conversions before the range
An example how it's done: In function ROW-MAJOR-AREF:
var uintV indexv = posfixnum_to_V(STACK_0);
if (indexv >= array_total_size(array)) /* index must be smaller
than size */
/* Only after indexv is known to be < size, we can safely cast
it to uintL: */
var uintL index = indexv;
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32 bits is far too little for the array limit.
this is a 64-bit world now.
there should be a way to address the whole of RAM,
be it 16GB or more.
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>32 bits is far too little for the array limit.
>this is a 64-bit world now.
This remembers me of tradeoff found in many databases:
Is it ok to use a 64bit array index when only very few if
any indices in an application will need so many bits?
Why is there a fixnum type, when all integers could be
represented using the bignum data structure?
Databases historically solve this using distinct types.
CLISP could do something similar, introducing a new array
type. But that would, again, cause code bloat and likely
more untested code.
For the near future, I'd prefer posfixnum_to_V code be
reviewed. I'm sure there are bugs left
> 32 bits is far too little for the array limit.
> this is a 64-bit world now.
Please mention a concrete, real use case that needs arrays
with more than 2^32 elements in a row. As far as I'm aware,
in Lisp it's commonplace to create data structures using many
objects, rather than huge arrays.
The machines I have access to have 512 MB RAM or less.
A year ago, LispWorks was still sold with an array dimension
limit of 2^16. This indicates that "a 64-bit world" is still a few
I'm closing this bug as "Postponed". Please reopen it when
the 64-bit world has arrived.
you are falling into the old fallacy of assuming that your
use pattern is everyone's use pattern.
remember a couple of years ago I needed multi-gig images and
you had to fix that functionality in a hurry (thanks for
helping me then!)
as far as I am aware, lisp philosophy has been to avoid
arbitrary limits on functionality (watch seamless
integration of bignums and fixnums) - and bot being able to
create huge arrays that is not a good idea.
limitations of other lisps is not a good reason to cripple
User subclassable array types would solve this issue and
provide other valuable extensions.
E.g. I've used the extendable SEQUENCE types to provide a
bridge to foreign arrays (unfinished code), so POSITION,
FIND and other sequence functions work on foreign array
It's dog slow (as all sequence functions), but could have
its uses. Better than sequence would IMHO be integration
with array functions (e.g. AREF on the foreign thing).
I mention that because I could believe (for the near future)
that if you allocate a >32bit array, then you don't want GC
to move that around. So malloc() is fine with it, so a
foreign<->array bridge would be enough for many needs
actually, this is the use case raised on clisp mailing lists
a few times in the past:
people want to use the normal lisp array functions on
a huge mmaped file.
they also want this access to be fast, i.e.,
without the FFI overhead.
I reviewed the bits in array.d which I thought were
problematic. They are not. I forgot that the C compiler
would DRT with a uint64 < uint32 comparison.
2. It's not trivial to add 64bit AREF access to a new
#<FOREIGN-ARRAY> type without touching the others, since
all C functions e.g. subscripts_to_index(), vector_length()
Actually, the integration work for such an addition is
independent on array-dimension-limit.
3. About "fast". The SEQUENCE functions in CLISP are
really generic and not fast at all anyway.
aref is fast enough and it does not cons.
64-bit access is indeed orthogonal to sequence functions
speeddup, but there is not reason not to do both.
64-bit computers are so common now - and will be even more
common soon - that any argument against doing as much as
possible in 64 bits reminds me of Tannenbaums criticism of
Linus reliance on i386 as being elitist and out of reach of
an average student user.
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