Re: [boost] [boost::endian] Request for comments/interest

Subject: Re: [boost] [boost::endian] Request for comments/interest
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2010-06-03 13:26:43

----- Original Message ----- 
From: "Terry Golubiewski" <tjgolubi_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Thursday, June 03, 2010 5:38 PM
Subject: Re: [boost] [boost::endian] Request for comments/interest

> 
> Tomas Puverle wrote:
> 
>>> > Swap Based: 18 seconds
>>> > Type Based   14 seconds
>>
>> This is unexpected...
> 
> Swap-then-copy is less efficient than just a reverse copy (in the general 
> case).
> These differences are more significant than I expected.  If we allow 9 
> seconds for the disk i/o and memcmp, then the overhead is approximately
> 
> Type-based: 36% overhead  (14-9)/14
> Swap-based: 50% overhead (18-9)/18.
 
Been a little more conservative: If we allow 6 seconds for the disk i/o and memcmp

Type-based:  (14-6)=8
Swap-based: (18-6)=12.

Ii.e; Swap-based spends 50%  more time than Type-based. 

>> Thanks again.  If there is a performance discrepancy between swap (soon to 
>> be
>> endian_cast<>) and the object-based approach, I will make sure to fix it,
>> of course.
> 
> If you implement endian_cast<> using a reverse-copy instead of swapping, you 
> will see a performance improvement.

You are right. Swap should make 50% more copies as a temporary is needed. This is in line with the figures.

Vicente