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Re: Using __builtin_add_overflow and friends for overflow checking

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James E Keenan
October 24, 2017 12:22
Re: Using __builtin_add_overflow and friends for overflow checking
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On 10/23/2017 05:34 PM, 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
> - benchmarks (compared to a17768d7c7b82c136fbeacd85db3451973a8007a)

1. You might want to rename your branch 'smoke-me/mauke/overflow'. 
Lacking the 'smoke-me/', it won't appear in the drop-down box at (even though will 
show it).

2. Please see these smoke-test reports on FreeBSD-10.3 and FreeBSD-11.0, 


I think the one test failure is spurious:  a side effect of resource 
constraints on this VM on my laptop.


Significant failures in t/op/numconvert.t.  Attaching output.

Thank you very much.
Jim Keenan

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