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Blitz Support : |
From: Frank Astier (fastier_at_[hidden])
Date: 2005-05-17 12:45:08
Hi -
I'm trying to use Blitz for a very simple mean computation on a 1D
vector of floats. I'm comparing to my own algorithm, which just does
a linear scan with N additions and a division. Compiling with -O2,
apparently, Blitz is slower... Am I missing some compilation flag to
make the thing go faster?
Here are the runtime results and the whole program, followed by my
implementation of mean (admittedly not safe):
Blitz: N = 5000000 mean = inf in 1.71s
Utils: N = 5000000 mean = inf in 1.6s
int main(int, char** argv) {
const size_t N = 5000000;
{
Array<double, 1> a(N);
for (size_t i = 0; i < N; ++i)
a(i) = double(rand() % 32768) / double(rand() % 65535);
timer t;
double m1 = mean(a);
cout << "Blitz: N = " << N << " mean = " << m1
<< " in " << t.elapsed() << endl;
}
{
vector<double> a(N);
for (size_t i = 0; i < N; ++i)
a[i] = double(rand() % 65535) / double(rand() % 32768);
timer t;
double m1 = mean(a);
cout << "Utils: N = " << N << " mean = " << m1
<< " in " << t.elapsed() << endl;
}
return 0;
}
//------------------------------------------------------------------------------
template <typename Iter1>
inline IteratorValueType mean(Iter1 first, Iter1 last)
{
// non empty ranges only
return sum(first, last) / (last - first);
}
//------------------------------------------------------------------------------
template <typename Container>
inline ContainerValueType mean(const Container& v)
{
return mean(v.begin(), v.end());
}
Frank