Re: [boost] Proposal/InterestCheck: Boost.Geom

Subject: Re: [boost] Proposal/InterestCheck: Boost.Geom
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2009-01-27 12:44:15

Anis Benyelloul wrote:
> (such as if you
> are packing the X and Y coordinates in the same machine word,
> geom::point<>::operator==() will be able to compare both coordinates with the
> same operation, instead of the generic x1==x2 && y1==y2). 

I have wondered about this particular optimisation before and your 
mention made me investigate.  gcc for ARM seems to make the 
optimisation but surprisingly the x86 version doesn't.  Test code:

struct pair {
   short a;
   short b;
};

int compare_pair(struct pair p1, struct pair p2)
{
   return p1.a==p2.a && p1.b==p2.b;
}

int compare_int(int i1, int i2)
{
   return i1==i2;
}

Is there anything in the language that makes this sort of thing 
difficult for the compiler?  I don't think so.

Phil.