quickSort.h

// This code is part of the Problem Based Benchmark Suite (PBBS)
// Copyright (c) 2013 Guy Blelloch and the PBBS team
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights (to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

#ifndef A_QSORT_INCLUDED
#define A_QSORT_INCLUDED
#include <algorithm>
#include "parallel.h"

template <class E, class BinPred, class intT>
void insertionSort(E* A, intT n, BinPred f) {
  for (intT i=0; i < n; i++) {
    E v = A[i];
    E* B = A + i;
    while (--B >= A && f(v,*B)) *(B+1) = *B;
    *(B+1) = v;
  }
}

#define ISORT 25

template <class E, class BinPred>
E median(E a, E b, E c, BinPred f) {
  return  f(a,b) ? (f(b,c) ? b : (f(a,c) ? c : a)) 
           : (f(a,c) ? a : (f(b,c) ? c : b));
}

// Quicksort based on median of three elements as pivot
//  and uses insertionSort for small inputs
template <class E, class BinPred, class intT>
void quickSort(E* A, intT n, BinPred f) {
  if (n < ISORT) insertionSort(A, n, f);
  else {
    //E p = std::__median(A[n/4],A[n/2],A[(3*n)/4],f);
    E p = median(A[n/4],A[n/2],A[(3*n)/4],f);
    E* L = A;   // below L are less than pivot
    E* M = A;   // between L and M are equal to pivot
    E* R = A+n-1; // above R are greater than pivot
    while (1) {
      while (!f(p,*M)) {
	if (f(*M,p)) std::swap(*M,*(L++));
	if (M >= R) break; 
	M++;
      }
      while (f(p,*R)) R--;
      if (M >= R) break; 
      std::swap(*M,*R--); 
      if (f(*M,p)) std::swap(*M,*(L++));
      M++;
    }
    cilk_spawn quickSort(A, L-A, f);
    quickSort(M, A+n-M, f); // Exclude all elts that equal pivot
    cilk_sync;
  }
}

#endif // _A_QSORT_INCLUDED