Bitonic Sort Algorithm
The Bitonic Sort Algorithm is an efficient parallel sorting algorithm, which is based on the concept of bitonic sequences. A bitonic sequence is defined as a sequence that is initially increasing and then decreasing, or a circular shift of such a sequence. The algorithm is designed to work well on parallel processing architectures, making it suitable for high-performance parallel computing systems. Bitonic sort is a comparison-based algorithm, meaning that it sorts data by comparing and exchanging pairs of elements within an array.
The Bitonic Sort Algorithm works by first constructing a bitonic sequence from the input data by recursively breaking it down into smaller subsequences, and then merging them back together. The merging process involves comparing pairs of elements from two subsequences and exchanging them if they are out of order, until the entire sequence is sorted. During the merge phase, the algorithm ensures that the output sequence is also bitonic, allowing it to be used as input for subsequent merge steps. This divide and conquer approach allows the Bitonic Sort Algorithm to achieve a time complexity of O(log^2(n)) for parallel implementations, making it an attractive choice for parallel computing systems.
// Source : https://www.geeksforgeeks.org/bitonic-sort/
/* C++ Program for Bitonic Sort. Note that this program
works only when size of input is a power of 2. */
#include <stdio.h>
#include <algorithm.h>
using namespace std;
/*The parameter dir indicates the sorting direction, ASCENDING
or DESCENDING; if (a[i] > a[j]) agrees with the direction,
then a[i] and a[j] are interchanged.*/
void compAndSwap(int a[], int i, int j, int dir)
{
if (dir == (a[i] > a[j]))
swap(a[i], a[j]);
}
/*It recursively sorts a bitonic sequence in ascending order,
if dir = 1, and in descending order otherwise (means dir=0).
The sequence to be sorted starts at index position low,
the parameter cnt is the number of elements to be sorted.*/
void bitonicMerge(int a[], int low, int cnt, int dir)
{
if (cnt > 1)
{
int k = cnt / 2;
for (int i = low; i < low + k; i++)
compAndSwap(a, i, i + k, dir);
bitonicMerge(a, low, k, dir);
bitonicMerge(a, low + k, k, dir);
}
}
/* This function first produces a bitonic sequence by recursively
sorting its two halves in opposite sorting orders, and then
calls bitonicMerge to make them in the same order */
void bitonicSort(int a[], int low, int cnt, int dir)
{
if (cnt > 1)
{
int k = cnt / 2;
// sort in ascending order since dir here is 1
bitonicSort(a, low, k, 1);
// sort in descending order since dir here is 0
bitonicSort(a, low + k, k, 0);
// Will merge wole sequence in ascending order
// since dir=1.
bitonicMerge(a, low, cnt, dir);
}
}
/* Caller of bitonicSort for sorting the entire array of
length N in ASCENDING order */
void sort(int a[], int N, int up)
{
bitonicSort(a, 0, N, up);
}
// Driver code
int main()
{
int a[] = {3, 7, 4, 8, 6, 2, 1, 5};
int N = sizeof(a) / sizeof(a[0]);
int up = 1; // means sort in ascending order
sort(a, N, up);
printf("Sorted array: \n");
for (int i = 0; i < N; i++)
printf("%d ", a[i]);
return 0;
}
