Re: [Boost-users] [accumulators] Is there a reset function yet?

Subject: Re: [Boost-users] [accumulators] Is there a reset function yet?
From: John Dlugosz (JDlugosz_at_[hidden])
Date: 2010-05-21 15:23:38

> > By the way, does the accumulator do something to prevent an overflow
> when I
> > add up everything into one variable?
> 
> No. It uses native intrinsics for raw performance. If you want anything
> fancy, you can use your own UDT for samples that check for overflow.
> Some construction required. :-( If you do build such a thing, I would
> consider making it an official part of Accumulators.
> Eric Niebler
> BoostPro Computing

Hey Eric, I wonder, did we cross paths back in the day, on Compuserve like DDJFORUM or CLMFORUM?  Your name is familiar.

I faced a similar overflow problem for general work.  I'm worried about adding signed and unsigned types, as well as different sizes of ints.  I made an overflow_add and overflow_subtract template that just does the work in a larger type if one is available, and does necessary checking for the largest type.  Rather than declare variables of some "checked" wrapper with its own overloaded operators, I just use overflow_add occasionally where needed.

It really bugs me that I could not draw upon the CPU's native checking.  It knows!  So why do I have to go out of my way to figure it out based on primitive principles?

I haven't done much writing lately, but I could share this with someone who wants to discuss it.  It would need a little work to make it more portable: I know what the largest type is.  Boost has a module that does fancy casting between integral types that is rather configurable; I know that an error is an overflow exception.  Undoubtedly the "policy" can be separated out from the tricky part of actually doing the detection for every possible case, making that reusable in a larger sense.

--John
John M. Dlugosz





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