Re: sub-optimal code for packed boolean arrays -- bug or inherent limitation

[Pascal Obry <pascal@obry.net>]

tmoran@acm.org a �crit :
> Using -O2 with the old gnat 3.15p on a 3GHz dual core Pentium (but only
> programming to use one core) under W2k, I find that the versions with
>         B(I) := not B(I);
> and
>         B(I) := B(I) xor True;
> take about 14 nanoseconds, while the version with
>         One(i) := True;
>         B   := B xor One;
> takes about 6.  With 1e9 calls, that's an 8 second difference.

That's not a proper timing. 3.15p is using a very old backend (2.x if my
memory is good). Since then there have been two major versions of the
GCC backend, both bringing better optimizations. It would be better to
do the measurement with GCC/FSF 4.2 or GNAT GPL 2007.

Pascal.

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