
Boost : 
From: Daniel Wesslén (daniel_at_[hidden])
Date: 20061203 07:04:37
I've just uploaded my matrix/vector library to the vault
(math2matrixvector, under Math  Geometry).
It's a library I was working on for a very long time a few years back,
trying to find the computationally most efficient one possible. The
reason I haven't shared it earlier is that I've come to believe that
keeping it simple is better, but now I see that vector swizzling is
being discussed, so...
The library uses expression templates for all componentwise operations
(so v1 = 2*v2 + v3 can be evaluated with no temporaries greater than a
float), has support for SSE2 vector intrinsics, and supports some
element reordering operations, including lvalue vector swizzling (v[zw]
= vector<2>(1,2) works).
Not all swizzlings are named, but if the one you happen to want is not
provided then it is easy to create:
const indexer<bits::index_swizzle<0,0,2,0> > xxzx;
const indexer<bits::index_swizzle<3,2,1,0> > wzyx;
vector<4> v1, v2(1,2,3,4);
v1 = v2[xxzx]; // v1 = (1,1,3,1)
v1[xxzx] = v2; // error  v1[xxzx] is not a lvalue due to aliasing
v1[wzyx] = v2; // v1 = (4,3,2,1)
Overall, I've found swizzling somewhat convenient, but far from
necessary. Nearly every time I used it it was to isolate xyz in a
4component vector.
 Daniel Wesslén
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk