# mathr / blog / #

## Exponential mapping and OpenMP

Robert Munafo pointed me at a cunning technique for transforming coordinates for optimizing zoom animation computations - it involves vastly less book-keeping than the ideas I've experimented with before and so makes it easier to do other clever things, like parallelizing with OpenMP:

...
do {
progress = 0;
#pragma omp parallel for private(p) reduction(||:progress) schedule(static, 1)
for (int x = 0; x < W; ++x) {
p = iteratePoint(y * W + x, count);
progress = progress || p;
}
} while (progress);
...

which leads to some impressive scaling benchmarks:

modetime
plain (1 thread)10m02s
OpenMP (1 thread)10m27s
OpenMP (2 threads)5m22s

Adding -fopenmp to the gcc flags is the only other thing needed to make it use another core and finish twice as quick, with attractive tall and thin results.