Super fast way to sort fixed integer arrays of size 7.

sort7.c

#include <cstdlib>
#include <ctime>
#include <cstdio>
#include <sys/time.h>
#include <sys/resource.h>

#define NTESTS (5000000)

static double get_time()
{
    struct timeval t;
    struct timezone tzp;
    gettimeofday(&t, &tzp);
    return t.tv_sec + t.tv_usec*1e-6;
}

static void sort7(int* a) {
#define max(x, y) (x ^ ((x ^ y) & -(x < y)))
#define min(x, y) (y ^ ((x ^ y) & -(x < y)))
#define SWAP(i, j) do { int temp = max(a[i], a[j]); a[i] = min(a[i], a[j]); a[j] = temp; } while(0)
    // sorting network from the site below:
    // http://pages.ripco.net/~jgamble/nw.html
    SWAP(1, 2); SWAP(0, 2); SWAP(0, 1); SWAP(3, 4);
    SWAP(5, 6); SWAP(3, 5); SWAP(4, 6); SWAP(4, 5);
    SWAP(0, 4); SWAP(0, 3); SWAP(1, 5); SWAP(2, 6);
    SWAP(2, 5); SWAP(1, 3); SWAP(2, 4); SWAP(2, 3);
#undef SWAP
#undef min
#undef max
}

int main() {
    srand(time(NULL));

    // init test cases
    int* arr = new int[7 * NTESTS];
    for (int i = 0; i < 7 * NTESTS; i++) {
        arr[i] = rand();
    }
    
    // begin testing
    double startTime = get_time();
    for (int i = 0; i < NTESTS; i++) {
        sort7(&arr[7 * i]);
    }
    double elapsed = get_time() - startTime;

    // verify
    for (int i = 0; i < NTESTS; i++) {
        for (int j = 0; j < 6; j++) {
            if (arr[7 * i + j] > arr[7 * i + j + 1]) {
                printf("FAILED!!!\n");
                return 1;
            }
        }
    }

    printf("Completed %d sorts in %lfs\n", NTESTS, elapsed);
}