[Rcpp-devel] Loops, iterators and accumulate

[Smith, Dale]

I'm not sure what compliers you are using out there, but gcc does have a way to enable warnings for this type of implicit conversion.

-Wconversion
Warn for implicit conversions that may alter a value. This includes conversions between real and integer...

http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Please check this, as it's not entirely obvious from the description that it will pick up a warning in this case.

Thanks,
Dale Smith, Ph.D.
Senior Financial Quantitative Analyst
Risk & Compliance
Fiserv.
107 Technology Park
Norcross, GA 30092
Office: 678-375-5315
Mail: dale.smith at fiserv.com
www.fiserv.com


-----Original Message-----
From: rcpp-devel-bounces at r-forge.wu-wien.ac.at [mailto:rcpp-devel-bounces at r-forge.wu-wien.ac.at] On Behalf Of Romain Francois
Sent: Thursday, November 15, 2012 9:18 AM
To: Hadley Wickham
Cc: rcpp-devel
Subject: Re: [Rcpp-devel] Loops, iterators and accumulate

Le 15/11/12 15:14, Hadley Wickham a écrit :
> On Thu, Nov 15, 2012 at 8:11 AM, Romain Francois 
> <romain at r-enthusiasts.com> wrote:
>> I'm not getting the same results, so I might not make the same conclusions:
>>
>>
>> Unit: microseconds
>>        expr    min     lq  median      uq    max
>> 1   sum(x) 16.072 16.161 16.2090 16.3110 21.721
>> 2  sum1(x) 10.771 10.954 11.0445 11.1910 16.163
>> 3  sum2(x) 48.438 48.567 48.6650 48.8425 61.116
>> 4 sum2a(x) 10.806 10.965 11.0695 11.2080 17.401
>> 5  sum3(x) 10.835 10.967 11.0490 11.1875 23.943
>> 6  sum4(x) 10.847 10.989 11.0690 11.2160 16.331
>>
>> For me that makes more sense.
>
> I just discovered the problem with my accumulate.  I was doing:
>
> double total = std::accumulate(x.begin(), x.end(), 0);
>
> instead of
>
> double total = std::accumulate(x.begin(), x.end(), 0.0);
>
> Hadley

Ah. Interesting. That makes sense, lots of conversion from double to int to accumulate into an int.

--
Romain Francois
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