.NET ProcessorAffinity计算

Question

I couldn't find any docs about how-to properly calculate affinity setting on c#'s ProcessorAffinity.

I'm passing a list of selected cores and adding them to get my final affinity setting however it seems my calculations are off.

How do you properly calculate the affinity based on a list of selected cores (0-32/64).

Also how could this be optimized?

if (!string.IsNullOrEmpty(affinitystr) && !affinitystr.Equals("-1"))
{
    string[] words = affinitystr.Split(',');
    int affinitytotal = 0;
    foreach (string word in words)
    {
        int affinity = Convert.ToInt32(word);
        if (affinity == 0) { affinity = 1; } // core 0
        else if (affinity == 1) { affinity = 2; } // core 1 
        else if (affinity == 2) { affinity = 4; } // core 2
        else if (affinity == 3) { affinity = 8; } // core 3
        else if (affinity == 4) { affinity = 10; } // core 4
        else if (affinity == 5) { affinity = 20; } // core 5
        else if (affinity == 6) { affinity = 40; } // core 6
        else if (affinity == 7) { affinity = 80; } // core 7
        else if (affinity == 8) { affinity = 100; } // core 8
        else if (affinity == 9) { affinity = 200; } // core 9
        else if (affinity == 10) { affinity = 400; } // core 10
        else if (affinity == 11) { affinity = 800; } // core 11
        else if (affinity == 12) { affinity = 1000; } // core 12
        else if (affinity == 13) { affinity = 2000; } // core 13
        else if (affinity == 14) { affinity = 4000; } // core 14
        else if (affinity == 15) { affinity = 8000; } // core 15
        else if (affinity == 16) { affinity = 10000; } // core 16
        else if (affinity == 17) { affinity = 20000; } // core 17
        else if (affinity == 18) { affinity = 40000; } // core 18
        else if (affinity == 19) { affinity = 80000; } // core 19
        else if (affinity == 20) { affinity = 100000; } // core 20
        else if (affinity == 21) { affinity = 200000; } // core 21
        else if (affinity == 22) { affinity = 400000; } // core 22
        else if (affinity == 23) { affinity = 800000; } // core 23
        else if (affinity == 24) { affinity = 1000000; } // core 24
        else if (affinity == 25) { affinity = 2000000; } // core 25
        else if (affinity == 26) { affinity = 4000000; } // core 26
        else if (affinity == 27) { affinity = 8000000; } // core 27
        else if (affinity == 28) { affinity = 10000000; } // core 28
        else if (affinity == 29) { affinity = 20000000; } // core 29
        else if (affinity == 30) { affinity = 40000000; } // core 30
        else if (affinity == 31) { affinity = 80000000; } // core 31
        else if (affinity == 32) { affinity = 100000000; } // core 32

        affinitytotal = affinitytotal + affinity;
    }

    scanProcess.ProcessorAffinity = (System.IntPtr)affinitytotal;
}

Answer 1

To get the affinity mask for a processor n (zero-based id), you just need to bit-shift the value 1 by n positions to the right.

string affinitystr  = "3,8,13";
long affinityMask = affinitystr.Split(',').Select(int.Parse).Sum(i => 1L << i);

Alternative formulation that uses ulong to properly represent up to 64 cores:

string affinitystr  = "3,8,13";
ulong affinityMask = affinitystr.Split(',')
                                .Select(int.Parse)
                                .Aggregate(0UL, (mask, id) => mask | (1UL << id));