Re: integer arithmetics

[John W. Eaton]

On  1-Oct-2008, Jaroslav Hajek wrote:

| On Wed, Oct 1, 2008 at 5:14 PM, John W. Eaton <address@hidden> wrote:
| > On 23-Sep-2008, Jaroslav Hajek wrote:
| >
| > | Sorry. I didn't realize that std::abs (int) is declared in cstdlib,
| > | not cmath. Please try again, same location. This new one should also
| > | get rid of the unused vars warnings you see.
| >
| > OK.
| >
| > I applied this changeset.
| >
| 
| Hmm, initially I didn't mean this to go into 3.2.x, but if you're fine
| with that, then why not.

Does it work?  If so, then I don't see why not.  I also built it with
HAVE_FAST_INT_OPS undefined and it seemed to build and function OK, at
least for the minimal tests I tried.

| Please consider also the attached patch, that
| fully implements the 64-bit arithmetics.
| If at least 80-bit wide long double type is discovered, it is used to
| implement 64-bit multiplication and mixed operations, otherwise, more
| complicated non-inline code is employed. In the latter case, some
| operations may suffer from precision loss (converting int64->double)
| or early truncation - see comments in oct-inttypes.cc. I think that
| the important cases (int64 +- double) are OK, and that one can live
| with losing precision when doing, for instance, 4611686018427387901 *
| 0.75. Maybe these emulations will be improved over time (though at a
| performance cost).

Do you mean this comment?

| +  // XXX: This trick is to not lose precision for things like 3*2**63 + 
intmin('int64')

Can you elaborate?

Also, please use FIXME instead of XXX since some people have
complained in the past about spam filters flagging mails that contain
XXX.

| OK to push?

Probably not yet.  What happened here:

| diff -r 1651939a394b -r 836df84b7997 doc/interpreter/contributors.in
| --- a/doc/interpreter/contributors.in Wed Oct 01 11:34:45 2008 -0400
| +++ b/doc/interpreter/contributors.in Wed Oct 01 20:16:39 2008 +0200
| @@ -193,7 +193,6 @@
|  Doug Stewart
|  Jonathan Stickel
|  Thomas Stuart
| -Ivan Sutoris
|  John Swensen
|  Ariel Tankus
|  Georg Thimm

?  I just added Ivan to this list.

jwe