Initial commit

Infra/Utils.cs

@@ -0,0 +1,56 @@
+using System.IO.MemoryMappedFiles;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using StitchATon2.Infra.Buffers;
+
+namespace StitchATon2.Infra;
+
+public static class Utils
+{
+    [UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_buffer")]
+    private static extern ref SafeBuffer GetSafeBuffer(this UnmanagedMemoryAccessor view);
+
+    [UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_offset")]
+    private static extern ref long GetOffset(this UnmanagedMemoryAccessor view);
+
+    private static unsafe uint AlignedSizeOf<T>() where T : unmanaged
+    {
+        uint size = (uint)sizeof(T);
+        return size is 1 or 2 ? size : (uint)((size + 3) & (~3));
+    }
+
+    public static void DangerousReadSpan<T>(this UnmanagedMemoryAccessor view, long position, Span<T> span, int offset, int count)
+        where T : unmanaged
+    {
+        uint sizeOfT = AlignedSizeOf<T>();
+        int n = count;
+        long spaceLeft = view.Capacity - position;
+        if (spaceLeft < 0)
+        {
+            n = 0;
+        }
+        else
+        {
+            ulong spaceNeeded = (ulong)(sizeOfT * count);
+            if ((ulong)spaceLeft < spaceNeeded)
+            {
+                n = (int)(spaceLeft / sizeOfT);
+            }
+        }
+
+        var byteOffset = (ulong)(view.GetOffset() + position);
+        view.GetSafeBuffer().ReadSpan(byteOffset, span.Slice(offset, n));
+    }
+
+    public static ArrayOwner<T> Clone<T>(this ArrayOwner<T> arrayOwner, int length) where T : unmanaged
+    {
+        var newArrayOwner = MemoryAllocator.AllocateArray<T>(length);
+        Array.Copy(arrayOwner.Array, 0, newArrayOwner.Array, 0, length);
+        return newArrayOwner;
+    }
+
+    public static void CopyTo<T>(this ArrayOwner<T> arrayOwner, ArrayOwner<T> target, int length) where T : unmanaged
+    {
+        Array.Copy(arrayOwner.Array, 0, target.Array, 0, length);
+    }
+}