Hi community,
Please find below a code snippet I wrote last night for generating the Carmichael’s numbers.
This demo was written in C# and it implements TPL to take advantage of multiple processors.
It is intended to be demoed at Tech-Ed Australia along with its counterpart written in C++ implementing PPL.
See you in two weeks time at Tech-Ed on the Gold Coast 
Best Regards,
Angel
using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.Collections.Concurrent;
using System.Runtime.InteropServices;
namespace Test2 {
class Program {
[DllImport("kernel32.dll", CallingConvention = CallingConvention.StdCall)]
private static extern int GetTickCount();
/// <summary>
/// Is_carmichaels the specified n.
/// </summary>
/// <param name="n">The n.</param>
/// <returns></returns>
static bool is_carmichael(int n) {
if (n < 2) { return false; }
int k = n;
for (int i = 2; i <= k / i; ++i) {
if (k % i == 0) {
if ((k / i) % i == 0) { return false; }
if ((n - 1) % (i - 1) != 0) { return false; }
k /= i;
i = 1;
}
}
return k != n && (n - 1) % (k - 1) == 0;
}
/// <summary>
/// Time_calls the specified functor.
/// </summary>
/// <param name="functor">The functor.</param>
/// <returns></returns>
static int time_call(Action functor) {
int begin = GetTickCount();
functor();
return GetTickCount() - begin;
}
/// <summary>
/// Mains the specified args.
/// </summary>
/// <param name="args">The args.</param>
static void Main(string[] args) {
int numItems = 10000000;
int numProcs = Environment.ProcessorCount;
var vectors = new ConcurrentBag<List<int>>();
Parallel.For(0, numProcs, (int i) => {
var v = new List<int>();
for (int j = numItems / numProcs * i; j < numItems / numProcs * (i + 1); ++j)
v.Add(j);
vectors.Add(v);
});
Console.WriteLine("Counting carmichael numbers");
// Serial
int sum, sum2, sum3;
var sums = new List<int>(numProcs);
var sums2 = new List<int>(numProcs);
var sums3 = new List<int>(numProcs);
int serialTime = time_call(() => vectors.ToList().ForEach(x => sums.Add(x.Count(z => is_carmichael(z)))));
sum = sums.Sum();
Console.WriteLine(string.Format(" {0} ms, num carmichaels {1}", new object[] { serialTime, sum }));
// Parallel
var task1 = Task.Factory.StartNew(() => {
int parallelTime2 = time_call(() => Parallel.ForEach(vectors, x => sums2.Add(x.Count(z => is_carmichael(z)))));
sum2 = sums2.AsParallel().Sum();
Console.WriteLine(string.Format(" {0} ms, num carmichaels {1}", new object[] { parallelTime2, sum2 }));
var task2 = Task.Factory.StartNew(() => {
int parallelTime3 = time_call(() => Parallel.ForEach(vectors, x => sums3.Add(x.Count(z => is_carmichael(z)))));
sum3 = sums3.AsParallel().Sum();
Console.WriteLine(string.Format(" {0} ms, num carmichaels {1}", new object[] { parallelTime3, sum3 }));
}, TaskCreationOptions.AttachedToParent);
});
task1.Wait();
Console.ReadKey();
}
}
}