shuffle.cs

using System.Runtime.Intrinsics;
using System.Runtime.Intrinsics.X86;

Vector128<byte> value = Vector128.Create((byte)0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);

Vector128<byte> mask = Vector128.Create((byte)0b01000100, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0);

// PSHUFB -- result[i] = (mask[i] & 0x80) ? 0 : value[mask[i] & 15]
Vector128<byte> result1 = Ssse3.Shuffle(value, mask);

// "Generic" (?) shuffle -- result[i] = (mask[i] < 16 ? 0 : value[mask[i]])
Vector128<byte> result2 = Vector128.Shuffle(value, mask);

Console.WriteLine(result1); // <3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>
Console.WriteLine(result2); // <0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0>