diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/System.Private.CoreLib/shared/System/Runtime/InteropServices/MemoryMarshal.Fast.cs | 62 |
1 files changed, 60 insertions, 2 deletions
diff --git a/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/MemoryMarshal.Fast.cs b/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/MemoryMarshal.Fast.cs index 967459e4b..8a5bb7539 100644 --- a/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/MemoryMarshal.Fast.cs +++ b/src/System.Private.CoreLib/shared/System/Runtime/InteropServices/MemoryMarshal.Fast.cs @@ -59,9 +59,38 @@ namespace System.Runtime.InteropServices if (RuntimeHelpers.IsReferenceOrContainsReferences<TTo>()) ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(TTo)); + // Use unsigned integers - unsigned division by constant (especially by power of 2) + // and checked casts are faster and smaller. + uint fromSize = (uint)Unsafe.SizeOf<TFrom>(); + uint toSize = (uint)Unsafe.SizeOf<TTo>(); + uint fromLength = (uint)source.Length; + int toLength; + if (fromSize == toSize) + { + // Special case for same size types - `(ulong)fromLength * (ulong)fromSize / (ulong)toSize` + // should be optimized to just `length` but the JIT doesn't do that today. + toLength = (int)fromLength; + } + else if (fromSize == 1) + { + // Special case for byte sized TFrom - `(ulong)fromLength * (ulong)fromSize / (ulong)toSize` + // becomes `(ulong)fromLength / (ulong)toSize` but the JIT can't narrow it down to `int` + // and can't eliminate the checked cast. This also avoids a 32 bit specific issue, + // the JIT can't eliminate long multiply by 1. + toLength = (int)(fromLength / toSize); + } + else + { + // Ensure that casts are done in such a way that the JIT is able to "see" + // the uint->ulong casts and the multiply together so that on 32 bit targets + // 32x32to64 multiplication is used. + ulong toLengthUInt64 = (ulong)fromLength * (ulong)fromSize / (ulong)toSize; + toLength = checked((int)toLengthUInt64); + } + return new Span<TTo>( ref Unsafe.As<TFrom, TTo>(ref source._pointer.Value), - checked((int)((long)source.Length * Unsafe.SizeOf<TFrom>() / Unsafe.SizeOf<TTo>()))); + toLength); } /// <summary> @@ -84,9 +113,38 @@ namespace System.Runtime.InteropServices if (RuntimeHelpers.IsReferenceOrContainsReferences<TTo>()) ThrowHelper.ThrowInvalidTypeWithPointersNotSupported(typeof(TTo)); + // Use unsigned integers - unsigned division by constant (especially by power of 2) + // and checked casts are faster and smaller. + uint fromSize = (uint)Unsafe.SizeOf<TFrom>(); + uint toSize = (uint)Unsafe.SizeOf<TTo>(); + uint fromLength = (uint)source.Length; + int toLength; + if (fromSize == toSize) + { + // Special case for same size types - `(ulong)fromLength * (ulong)fromSize / (ulong)toSize` + // should be optimized to just `length` but the JIT doesn't do that today. + toLength = (int)fromLength; + } + else if (fromSize == 1) + { + // Special case for byte sized TFrom - `(ulong)fromLength * (ulong)fromSize / (ulong)toSize` + // becomes `(ulong)fromLength / (ulong)toSize` but the JIT can't narrow it down to `int` + // and can't eliminate the checked cast. This also avoids a 32 bit specific issue, + // the JIT can't eliminate long multiply by 1. + toLength = (int)(fromLength / toSize); + } + else + { + // Ensure that casts are done in such a way that the JIT is able to "see" + // the uint->ulong casts and the multiply together so that on 32 bit targets + // 32x32to64 multiplication is used. + ulong toLengthUInt64 = (ulong)fromLength * (ulong)fromSize / (ulong)toSize; + toLength = checked((int)toLengthUInt64); + } + return new ReadOnlySpan<TTo>( ref Unsafe.As<TFrom, TTo>(ref MemoryMarshal.GetReference(source)), - checked((int)((long)source.Length * Unsafe.SizeOf<TFrom>() / Unsafe.SizeOf<TTo>()))); + toLength); } /// <summary> |