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Re: Using __builtin_add_overflow and friends for overflow checking

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Shlomi Fish
October 24, 2017 08:38
Re: Using __builtin_add_overflow and friends for overflow checking
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Hi Lukas,

On Mon, 23 Oct 2017 23:34:16 +0200
Lukas Mai <> wrote:

> I think it would be a good idea to use compiler intrinsics for overflow 
> checks where available.
> I've pushed a branch that implements this at mauke/overflow:
> Dave: I've CC'd you directly because you last worked on this code 
> (commit 230ee21f3e366901ce5769d324124c522df7ce8a, "faster add, subtract, 
> multiply").
> My changes affect pp_add, pp_subtract, and pp_multiply. I think the new 
> code is nicer because it's easier to understand than all the low-level 
> bit fiddling, and it passes all tests on my machine. However, I haven't 
> done any benchmarks to see how it affects performance (if at all).
> Things I need help with:
> - code review
> - testing on different platforms / architectures

I am getting test failures here (Mageia 7 x86-64 after the "b" and "t"
functions from - ;
on this system:

My primary machine is a desktop machine with a:

    An Intel Core i3 CPU (x86-64).
    8 GB of RAM.
    Intel Corporation Sandy Bridge Integrated Graphics Controller (rev 09)
    A 2 TB hard-disk.
    A 21″ Wide LCD Screen by LG.
    Intel Corporation Cougar Point High Definition Audio Controller.
    Intel Corporation 82579V Gigabit Network Connection.

Test Summary Report
op/numconvert.t                                                  (Wstat: 0
Tests: 1444 Failed: 3) Failed tests:  104, 108, 112
Files=2619, Tests=1141848, 562 wallclock secs (107.37 usr 10.03 sys + 1108.68
cusr 57.37 csys = 1283.45 CPU) Result: FAIL
make: *** [makefile:833: test_harness] Error 3
n --msg perl/core test finished

> - benchmarks (compared to a17768d7c7b82c136fbeacd85db3451973a8007a)

Shlomi Fish
Escape from GNU Autohell -

When a FLOSS developer says they will work on something, he or she means

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