Fabulous performance optimization 3-4X for the worst-case of a constant array, which also makes sense for all other cases and doesn't make a special case for constant array.

Author: DragonSpit

HPCsharp/SelectionRadix.cs

@@ -38,15 +38,16 @@ private static void RadixSelectiontMsdUIntInner(uint[] a, int first, int length,
  if (binLength == 0) continue; // skip empty bins
  if (k >= startOfBin[kthBin] && k <= (startOfBin[kthBin + 1] - 1)) break;
  }
- int _current_ob = first, _current_ib = startOfBin[kthBin]; // _ob = outside of bin, _ib = inside of bin
+ int _current_ob = first, _current_ib = startOfBin[kthBin], found_ob; // _ob = outside of bin, _ib = inside of bin
  while (true) // process elements outside the bin that k is in, which are to the left of that bin
  {
  // Look for the element that belongs in the bin that k is in, to move into that bin
- for (; _current_ob < startOfBin[kthBin]; _current_ob++)
- if (((a[_current_ob] >> shiftRightAmount) & bitMask) == kthBin) break;
+ for (found_ob = 0; _current_ob < startOfBin[kthBin]; _current_ob++)
+ if (((a[_current_ob] >> shiftRightAmount) & bitMask) == kthBin) { found_ob = 1; break; }
  // Look for the first location in the bin that k is in, which has an element that does not belong in that bin
- for (; _current_ib < startOfBin[kthBin + 1]; _current_ib++)
- if (((a[_current_ib] >> shiftRightAmount) & bitMask) != kthBin) break;
+ if (found_ob == 1)
+ for (; _current_ib < startOfBin[kthBin + 1]; _current_ib++)
+ if (((a[_current_ib] >> shiftRightAmount) & bitMask) != kthBin) break;
 
  if (_current_ib >= startOfBin[kthBin + 1] || _current_ob >= startOfBin[kthBin]) break; // The bin that k is in is full or all the element outside the bin to the left have been exhausted
  a[_current_ib++] = a[_current_ob++]; // Move the element that belongs in the bin into the bin
@@ -55,11 +56,12 @@ private static void RadixSelectiontMsdUIntInner(uint[] a, int first, int length,
  while (true) // process elements outside the bin that k is in, which are to the right of that bin
  {
  // Look for the element that belongs in the bin that k is in, to move into that bin
- for (; _current_ob <= last; _current_ob++)
- if (((a[_current_ob] >> shiftRightAmount) & bitMask) == kthBin) break;
+ for (found_ob = 0; _current_ob <= last; _current_ob++)
+ if (((a[_current_ob] >> shiftRightAmount) & bitMask) == kthBin) { found_ob = 1; break; }
  // Look for the first location in the bin that k is in, which has an element that does not belong in that bin
- for (; _current_ib < startOfBin[kthBin + 1]; _current_ib++)
- if (((a[_current_ib] >> shiftRightAmount) & bitMask) != kthBin) break;
+ if (found_ob == 1)
+ for (; _current_ib < startOfBin[kthBin + 1]; _current_ib++)
+ if (((a[_current_ib] >> shiftRightAmount) & bitMask) != kthBin) break;
 
  if (_current_ib >= startOfBin[kthBin + 1] || _current_ob > last) break; // The bin that k is in is full or all the element outside the bin to the right have been exhausted
  a[_current_ib++] = a[_current_ob++]; // Move the element that belongs in the bin into the bin