document zero initialization vs. loading

Author: Nick-Nuon

src/Ascii.cs

@@ -92,16 +92,69 @@ public static unsafe bool SIMDIsAscii(this ReadOnlySpan<char> s)
                 fixed (char* pStart = &MemoryMarshal.GetReference(s))
                 {
                     int i = 0;
+
+/* PAR Unrolled twice:
+|                 Method |   N |       Mean |    Error |   StdDev |
+|----------------------- |---- |-----------:|---------:|---------:|
+|     FastUnicodeIsAscii | 100 |   905.7 ns | 17.95 ns | 20.67 ns |
+| StandardUnicodeIsAscii | 100 | 2,502.4 ns | 49.67 ns | 66.31 ns |
+|         RuntimeIsAscii | 100 | 2,522.8 ns | 32.70 ns | 30.59 ns |
+|     FastUnicodeIsAscii | 200 |   649.3 ns | 10.24 ns |  9.57 ns |
+| StandardUnicodeIsAscii | 200 | 5,299.7 ns | 64.91 ns | 57.54 ns |
+|         RuntimeIsAscii | 200 | 5,307.2 ns | 49.18 ns | 46.00 ns |
+|     FastUnicodeIsAscii | 500 | 1,382.2 ns |  9.40 ns |  8.79 ns |
+| StandardUnicodeIsAscii | 500 | 6,127.7 ns | 57.69 ns | 48.18 ns |
+|         RuntimeIsAscii | 500 | 6,258.2 ns | 62.05 ns | 58.05 ns | */
+
+                    // if (s.Length > 16)  // Adjusted for the unrolled loop
+                    // {
+                    //     Vector128<ushort> total = Sse41.LoadDquVector128((ushort*)pStart);
+                    //     i += 8;
+
+                    //     // Unrolling the loop by 2x
+                    //     for (; i + 15 < s.Length; i += 16)
+                    //     {
+                    //         Vector128<ushort> raw1 = Sse41.LoadDquVector128((ushort*)pStart + i);
+                    //         Vector128<ushort> raw2 = Sse41.LoadDquVector128((ushort*)pStart + i + 8);
+                            
+                    //         total = Sse2.Or(total, raw1);
+                    //         total = Sse2.Or(total, raw2); 
+                    //     }
+
+                    //     Vector128<ushort> b127 = Vector128.Create((ushort)127);
+                    //     Vector128<ushort> b = Sse41.Max(b127, total);
+                    //     Vector128<ushort> b16 = Sse41.CompareEqual(b, b127);
+                    //     int movemask = Sse2.MoveMask(b16.AsByte());
+                    //     if (movemask != 0xffff)
+                    //     {
+                    //         return false;
+                    //     }
+                    // }
+
+// |                 Method |   N |       Mean |    Error |   StdDev |
+// |----------------------- |---- |-----------:|---------:|---------:|
+// |     FastUnicodeIsAscii | 100 |   904.0 ns |  9.22 ns |  8.17 ns |
+// | StandardUnicodeIsAscii | 100 | 2,396.5 ns | 11.33 ns | 10.04 ns |
+// |         RuntimeIsAscii | 100 | 2,498.8 ns | 42.35 ns | 37.54 ns |
+// |     FastUnicodeIsAscii | 200 | 1,270.0 ns |  7.69 ns |  6.01 ns |
+// | StandardUnicodeIsAscii | 200 | 5,173.0 ns | 57.82 ns | 54.08 ns |
+// |         RuntimeIsAscii | 200 | 5,197.5 ns | 15.40 ns | 13.65 ns |
+// |     FastUnicodeIsAscii | 500 | 1,412.0 ns | 24.22 ns | 21.47 ns |
+// | StandardUnicodeIsAscii | 500 | 6,196.5 ns | 60.78 ns | 53.88 ns |
+// |         RuntimeIsAscii | 500 | 6,215.5 ns | 96.43 ns | 90.20 ns |
+
+
                     if (s.Length > 16)  // Adjusted for the unrolled loop
                     {
-                        Vector128<ushort> total = Sse41.LoadDquVector128((ushort*)pStart);
+                        // Using zeroed vector as initialization
+                        Vector128<ushort> total = Vector128<ushort>.Zero;
                         i += 8;
 
                         // Unrolling the loop by 2x
-                        for (; i + 15 < s.Length; i += 16)
+                        for (; i + 16 < s.Length; i += 16)
                         {
-                            Vector128<ushort> raw1 = Sse41.LoadDquVector128((ushort*)pStart + i);
-                            Vector128<ushort> raw2 = Sse41.LoadDquVector128((ushort*)pStart + i + 8);
+                            Vector128<ushort> raw1 = Sse41.LoadDquVector128((ushort*)pStart);
+                            Vector128<ushort> raw2 = Sse41.LoadDquVector128((ushort*)pStart + i);
 
                             total = Sse2.Or(total, raw1);
                             total = Sse2.Or(total, raw2); 
@@ -116,6 +169,7 @@ public static unsafe bool SIMDIsAscii(this ReadOnlySpan<char> s)
                             return false;
                         }
                     }
+
                     for (; i < s.Length; i++)
                     {
                         if (pStart[i] >= 128) return false;