Re: [clisp-list] array index limits

[<don...@is...>]

Bruno Haible writes:

 > The maximum size for arrays and strings is driven by the desire to have only
 > two header words per instance. It is a compromise. One could also choose to
 > have all arrays and all strings with three header words per instance. This
 > would increase the memory size by a certain percentage and the run time of
 > all programs by twice this percentage (according to Michael Monagan's
 > rule that when the memory use of a program increases by a factor X, its
 > use of time increases by a factor X^2).
I'm not familar with that rule.  What ever became of time/space tradeoffs?
Certainly there are lots of small arrays (especially strings), and it would 
be nice to be able to represent them with low overhead.  
In fact, I suggest that for strings that are short enough, it would
make sense to have a representation analogous to fixnum, i.e., one
other 8 bit type code for short string.
By the time you get to large arrays, the difference between 2 and 3
header words doesn't matter.  So it would make sense to have another
type for large arrays.

 >     but as Sam mentioned, ARRAY-DIMENSION-LIMIT must be a fixnum. and
 >     MOST-POSITIVE-FIXNUM is 2^24-1. 24 = oint_data_len.
Even worse, array total size must be a fixnum.
I wonder why the writers of the spec made that decision.  (Any ideas?)
It seems absurd to me right now.
Perhaps there could be yet another type for BIG Arrays.
I know, I should implement that type in CLOS.
I'm tempted to do so.  If someone out there beats me to it I won't object.

 > You can write an abstraction of very long arrays, say in terms of
 > an array of arrays, in about 50 lines of code. With clisp's
 > extensible sequences, you can can even use the normal sequence
 > functions on it. Refer to SYS::%DEFSEQ.
I see, it might have been worth reading the rest of the message before
typing the last few sentences.
I guess I can't change functions like aref without violating the spec.
So I'd have to change my code to use the new functions.

Does anyone out there already have a very large array package?