Rewrite decompressor RefillTagFromScatch method to use refs (#49)

Motivation ---------- This is a step towards code that doesn't require pinning which can help with GC when compression/decompression is run a lot. GC will be able to move memory even when in the middle of a compression or decompression run and update the ref pointers. Modifications ------------- Rewrite RefillTagFromScratch to use refs, returning a ValueTuple so that the pointer may be incremented the correct amount by the caller. Results ------- .NET 6 shows a per improvement, .NET 7 is neutral. .NET 4.8 shows a slight regression, I'm assuming due to poor enregistration. BenchmarkDotNet=v0.13.4, OS=Windows 11 (10.0.22000.1455/21H2) Intel Core i7-10850H CPU 2.70GHz, 1 CPU, 12 logical and 6 physical cores .NET SDK=7.0.102 [Host] : .NET 7.0.2 (7.0.222.60605), X64 RyuJIT AVX2 MediumRun-.NET 6.0 : .NET 6.0.13 (6.0.1322.58009), X64 RyuJIT AVX2 MediumRun-.NET 7.0 : .NET 7.0.2 (7.0.222.60605), X64 RyuJIT AVX2 MediumRun-.NET Framework 4.8 : .NET Framework 4.8 (4.8.4515.0), X64 RyuJIT VectorSize=256 IterationCount=15 LaunchCount=2 WarmupCount=10 | Method | Job | Runtime | Mean | Error | StdDev | Median | Ratio | RatioSD | |-------- |----------------------------- |------------------- |----------:|---------:|---------:|----------:|------:|--------:| | Pointer | MediumRun-.NET 6.0 | .NET 6.0 | 109.06 us | 1.150 us | 1.686 us | 108.60 us | 1.00 | 0.00 | | Ref | MediumRun-.NET 6.0 | .NET 6.0 | 106.20 us | 0.863 us | 1.265 us | 106.47 us | 0.97 | 0.02 | | | | | | | | | | | | Pointer | MediumRun-.NET 7.0 | .NET 7.0 | 93.34 us | 0.877 us | 1.257 us | 93.13 us | 1.00 | 0.00 | | Ref | MediumRun-.NET 7.0 | .NET 7.0 | 94.00 us | 1.161 us | 1.738 us | 95.01 us | 1.01 | 0.03 | | | | | | | | | | | | Pointer | MediumRun-.NET Framework 4.8 | .NET Framework 4.8 | 106.36 us | 0.357 us | 0.501 us | 106.42 us | 1.00 | 0.00 | | Ref | MediumRun-.NET Framework 4.8 | .NET Framework 4.8 | 111.34 us | 1.041 us | 1.558 us | 110.50 us | 1.05 | 0.02 |
brantburnett · Feb 6, 2023 · 8a631ce · 8a631ce
1 parent 130b5ba
commit 8a631ce
Showing 1 changed file with 12 additions and 11 deletions.
diff --git a/Snappier/Internal/SnappyDecompressor.cs b/Snappier/Internal/SnappyDecompressor.cs
@@ -210,7 +210,10 @@ internal unsafe void DecompressAllTags(ReadOnlySpan<byte> inputSpan)
                                 // and any literal data from the _input buffer
 
                                 // scratch will be the scratch buffer with only the tag if true is returned
-                                if (!RefillTagFromScratch(ref input, inputEnd, scratch))
+                                (bool sufficientData, uint inputUsed) = RefillTagFromScratch(ref Unsafe.AsRef<byte>(input),
+                                    ref Unsafe.AsRef<byte>(inputEnd), ref Unsafe.AsRef<byte>(scratch));
+                                input += inputUsed;
+                                if (!sufficientData)
                                 {
                                     return;
                                 }
@@ -416,33 +419,31 @@ internal unsafe void DecompressAllTags(ReadOnlySpan<byte> inputSpan)
             }
         }
 
-        private unsafe bool RefillTagFromScratch(ref byte* input, byte* inputEnd, byte* scratch)
+        private (bool sufficientData, uint inputUsed) RefillTagFromScratch(ref byte input, ref byte inputEnd, ref byte scratch)
         {
             Debug.Assert(_scratchLength > 0);
 
-            if (input >= inputEnd)
+            if (!Unsafe.IsAddressLessThan(ref input, ref inputEnd))
             {
-                return false;
+                return (false, 0);
             }
 
             // Read the tag character
-            byte c = *scratch;
-            uint entry = Constants.CharTable[c];
+            uint entry = Constants.CharTable[scratch];
             uint needed = (entry >> 11) + 1; // +1 byte for 'c'
 
-            uint toCopy = Math.Min(unchecked((uint)(inputEnd - input)), needed - _scratchLength);
-            Unsafe.CopyBlockUnaligned(scratch + _scratchLength, input, toCopy);
+            uint toCopy = Math.Min((uint)Unsafe.ByteOffset(ref input, ref inputEnd), needed - _scratchLength);
+            Unsafe.CopyBlockUnaligned(ref Unsafe.Add(ref scratch, _scratchLength), ref input, toCopy);
 
             _scratchLength += toCopy;
-            input += toCopy;
 
             if (_scratchLength < needed)
             {
                 // Still insufficient
-                return false;
+                return (false, toCopy);
             }
 
-            return true;
+            return (true, toCopy);
         }
 
         private unsafe bool RefillTag(ref byte* input, ref byte* inputEnd, byte* scratch)