public static void RadixSort(Testing[] a)
{
// our helper array
Testing[] t = new Testing[a.Length];
// number of bits our group will be long
int r = 4; // try to set this also to 2, 8 or 16 to see if it is quicker or not
// number of bits of a C# int
int b = 32;
// counting and prefix arrays
// (note dimensions 2^r which is the number of all possible values of a r-bit number)
int[] count = new int[1 << r];
int[] pref = new int[1 << r];
// number of groups
int groups = (int)Math.Ceiling((double)b / (double)r);
// the mask to identify groups
int mask = (1 << r) - 1;
// the algorithm:
for (int c = 0, shift = 0; c < groups; c++, shift += r)
{
// reset count array
for (int j = 0; j < count.Length; j++)
{
count[j] = 0;
}
// counting elements of the c-th group
for (int i = 0; i < a.Length; i++)
{
count[(a[i].Key >> shift) & mask]++;
}
// calculating prefixes
pref[0] = 0;
for (int i = 1; i < count.Length; i++)
{
pref[i] = pref[i - 1] + count[i - 1];
}
// from a[] to t[] elements ordered by c-th group
for (int i = 0; i < a.Length; i++)
{
t[pref[(a[i].Key >> shift) & mask]++] = a[i];
}
// a[]=t[] and start again until the last group
t.CopyTo(a, 0);
}
// a is sorted
}
