On Fri, Nov 24, 2017 at 5:25 AM, lkintact <[email protected]> wrote:
> Type a large number, for example 999999999999999999999999.
> Switch to Normal mode, put the cursor on the number and hit Ctrl-x. The
> number changes to 18446744073709551614. (this seems to be intended, perhaps
> gVim changes too large a number to the largest possible value for the type).
> Hit Ctrl-x again, nothing happens, that is 18446744073709551614 isn't
> reduced by 1, while expected.
> Hit Ctrl-a. 18446744073709551614 changes to -18446744073709551615 (this
> seems to be intended too).
> Hit Ctrl-a again, -18446744073709551615 changes to -18446744073709551614 as
> expected.
> Hit Ctrl-a one more time, nothing happens, that is -18446744073709551614
> isn't increased by 1, while expected.
>
> Win 7 SP1,
> gVim 8.0.1333 x86
>

I see the same on gvim 8.0.1333 with GTK2-Gnome GUI (x86_64) on
openSUSE Linux 42.3.

I think this is related to how Vim emulates NaN, INF and -INF for
integer numbers, see the second half of the help text between |expr6|
and |expr7|. I suppose it makes some sense that -INF + 1 == -INF. What
in fact surprises me more is that +INF + 1 results apparently in -INF.
Maybe a result of an uncaught arithmetic overflow somewhere.

Best regards,
Tony.

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