Re: faster std::accumulate, via metaprogramming
strnbrg@trhj.homeunix.net wrote:
For adding up the elements of an int[4] (say) v[0]+v[1]+v[2]+v[3] is
about nine times faster that std::accumulate (gcc-4.0.1, -O6).
This...
----------------------------------------------------------
template<int N> long accum( const long* v )
{
return v[N-1] + accum<N-1>(v);
}
template<> long accum<1>( const long* v )
{
return v[0];
}
-----------------------------------------------------------
...is as fast as v[0]+v[1]+v[2]+v[3]. So far so good. Unfortunately,
I'd really rather use STL, than write things like this and moreover,
with earlier gcc versions, this template of mine is actually slower
than std::accumulate.
I know I can't expect STL to beat handwritten codeeverywhere, but
shouldn't we expect better than a 9x performance hit?
Uh... Did you manage to pass a variable (not compile time constant) to
your 'accum' template as the template argument or were you testing with
the hard-coded 4? How much of your program is data-independent and has
hard-coded numerical values?
V
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