Fastest code C/C++ to select the median in a set of 27 floating point values

Question

This is the well know select algorithm. see http://en.wikipedia.org/wiki/Selection_algorithm.

I need it to find the median value of a set of 3x3x3 voxel values. Sinc

Answer 1

You might want to have a look at Knuth's Exercise 5.3.3.13. It describes an algorithm due to Floyd that finds the median of n elements using (3/2)n+O(n^(2/3) log n) comparisons, and the constant hidden in the O(·) seems not to be too large in practice.