Add NativeMemory.ZeroMemory API (dotnet#69500)

* Add NativeMemory.ZeroMemory API

* Replace Random.NextBytes with Span<byte>.Fill

* Add ZeroMemory unit tests for zeroed region within buffer

* Add remarks for ptr and byteCount parameters

* Add test for ZeroMemory(null, 0) not throwing

* Add unit tests for zeroing memory with a size of 0

* Move test cases with 0 byte count to separate method

Co-authored-by: Stephen Toub <stoub@microsoft.com>

src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/NativeMemory.cs

@@ -38,6 +38,19 @@ public static unsafe partial class NativeMemory
             return AllocZeroed(byteCount, elementSize: 1);
         }
 
+        /// <summary>Clears a block of memory.</summary>
+        /// <param name="ptr">A pointer to the block of memory that should be cleared.</param>
+        /// <param name="byteCount">The size, in bytes, of the block to clear.</param>
+        /// <remarks>
+        ///     <para>If this method is called with <paramref name="ptr" /> being <see langword="null"/> and <paramref name="byteCount" /> being <c>0</c>, it will be equivalent to a no-op.</para>
+        ///     <para>The behavior when <paramref name="ptr" /> is <see langword="null"/> and <paramref name="byteCount" /> is greater than <c>0</c> is undefined.</para>
+        /// </remarks>
+        [CLSCompliant(false)]
+        public static unsafe void ZeroMemory(void* ptr, nuint byteCount)
+        {
+            SpanHelpers.ClearWithoutReferences(ref *(byte*)ptr, byteCount);
+        }
+
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static nuint GetByteCount(nuint elementCount, nuint elementSize)
         {

src/libraries/System.Runtime.InteropServices/ref/System.Runtime.InteropServices.cs

@@ -809,6 +809,8 @@ public static void AlignedFree(void* ptr) { }
         public static void Free(void* ptr) { }
         [System.CLSCompliantAttribute(false)]
         public static void* Realloc(void* ptr, nuint byteCount) { throw null; }
+        [System.CLSCompliantAttribute(false)]
+        public static void ZeroMemory(void* ptr, nuint byteCount) { throw null; }
     }
     public readonly partial struct NFloat : System.IComparable, System.IComparable<System.Runtime.InteropServices.NFloat>, System.IEquatable<System.Runtime.InteropServices.NFloat>, System.IFormattable, System.IParsable<System.Runtime.InteropServices.NFloat>, System.ISpanFormattable, System.ISpanParsable<System.Runtime.InteropServices.NFloat>, System.Numerics.IAdditionOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IAdditiveIdentity<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IBinaryFloatingPointIeee754<System.Runtime.InteropServices.NFloat>, System.Numerics.IBinaryNumber<System.Runtime.InteropServices.NFloat>, System.Numerics.IBitwiseOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IComparisonOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IDecrementOperators<System.Runtime.InteropServices.NFloat>, System.Numerics.IDivisionOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IEqualityOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IExponentialFunctions<System.Runtime.InteropServices.NFloat>, System.Numerics.IFloatingPoint<System.Runtime.InteropServices.NFloat>, System.Numerics.IFloatingPointIeee754<System.Runtime.InteropServices.NFloat>, System.Numerics.IHyperbolicFunctions<System.Runtime.InteropServices.NFloat>, System.Numerics.IIncrementOperators<System.Runtime.InteropServices.NFloat>, System.Numerics.ILogarithmicFunctions<System.Runtime.InteropServices.NFloat>, System.Numerics.IMinMaxValue<System.Runtime.InteropServices.NFloat>, System.Numerics.IModulusOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IMultiplicativeIdentity<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IMultiplyOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.INumber<System.Runtime.InteropServices.NFloat>, System.Numerics.INumberBase<System.Runtime.InteropServices.NFloat>, System.Numerics.IPowerFunctions<System.Runtime.InteropServices.NFloat>, System.Numerics.IRootFunctions<System.Runtime.InteropServices.NFloat>, System.Numerics.ISignedNumber<System.Runtime.InteropServices.NFloat>, System.Numerics.ISubtractionOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.ITrigonometricFunctions<System.Runtime.InteropServices.NFloat>, System.Numerics.IUnaryNegationOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>, System.Numerics.IUnaryPlusOperators<System.Runtime.InteropServices.NFloat, System.Runtime.InteropServices.NFloat>
     {

src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/NativeMemoryTests.cs

@@ -435,5 +435,128 @@ public void ReallocSmallerToLargerTest()
 
             NativeMemory.Free(newPtr);
         }
+
+        [Theory]
+        [InlineData(1, 0)]
+        [InlineData(1, 1)]
+        [InlineData(1, 2)]
+        [InlineData(1, 3)]
+        [InlineData(2, 0)]
+        [InlineData(3, 0)]
+        [InlineData(4, 0)]
+        [InlineData(8, 0)]
+        [InlineData(9, 0)]
+        [InlineData(16, 0)]
+        [InlineData(16, 1)]
+        [InlineData(16, 3)]
+        [InlineData(16, 7)]
+        [InlineData(32, 0)]
+        [InlineData(64, 0)]
+        [InlineData(128, 0)]
+        [InlineData(256, 0)]
+        [InlineData(256, 1)]
+        [InlineData(256, 2)]
+        [InlineData(256, 3)]
+        [InlineData(256, 5)]
+        [InlineData(512, 0)]
+        [InlineData(547, 0)]
+        [InlineData(1 * 1024, 0)]
+        public void ZeroMemoryTest(int size, int offset)
+        {
+            byte* ptr = (byte*)NativeMemory.AlignedAlloc((nuint)(size + offset), 8);
+
+            Assert.True(ptr != null);
+            Assert.True((nuint)ptr % 8 == 0);
+
+            new Span<byte>(ptr, size + offset).Fill(0b10101010);
+
+            NativeMemory.ZeroMemory(ptr + offset, (nuint)size);
+
+            Assert.Equal(-1, new Span<byte>(ptr + offset, size).IndexOfAnyExcept((byte)0));
+
+            NativeMemory.AlignedFree(ptr);
+        }
+
+        [Theory]
+        [InlineData(1, 0)]
+        [InlineData(1, 1)]
+        [InlineData(1, 2)]
+        [InlineData(1, 3)]
+        [InlineData(1, 44)]
+        [InlineData(1, 367)]
+        [InlineData(2, 0)]
+        [InlineData(3, 0)]
+        [InlineData(4, 0)]
+        [InlineData(8, 0)]
+        [InlineData(9, 0)]
+        [InlineData(9, 2)]
+        [InlineData(9, 111)]
+        [InlineData(9, 289)]
+        [InlineData(16, 0)]
+        [InlineData(16, 1)]
+        [InlineData(16, 3)]
+        [InlineData(16, 7)]
+        [InlineData(32, 0)]
+        [InlineData(64, 0)]
+        [InlineData(128, 0)]
+        [InlineData(256, 0)]
+        [InlineData(256, 1)]
+        [InlineData(256, 2)]
+        [InlineData(256, 3)]
+        [InlineData(256, 5)]
+        [InlineData(256, 67)]
+        [InlineData(256, 143)]
+        public void ZeroMemoryWithExactRangeTest(int size, int offset)
+        {
+            int headLength = offset;
+            int bodyLength = size;
+            int tailLength = 512 - headLength - bodyLength;
+            int headOffset = 0;
+            int bodyOffset = headLength;
+            int tailOffset = headLength + bodyLength;
+
+            byte* ptr = (byte*)NativeMemory.AlignedAlloc(512, 8);
+
+            Assert.True(ptr != null);
+            Assert.True((nuint)ptr % 8 == 0);
+
+            new Span<byte>(ptr, 512).Fill(0b10101010);
+
+            NativeMemory.ZeroMemory(ptr + bodyOffset, (nuint)bodyLength);
+
+            Assert.Equal(-1, new Span<byte>(ptr + headOffset, headLength).IndexOfAnyExcept((byte)0b10101010));
+            Assert.Equal(-1, new Span<byte>(ptr + bodyOffset, bodyLength).IndexOfAnyExcept((byte)0));
+            Assert.Equal(-1, new Span<byte>(ptr + tailOffset, tailLength).IndexOfAnyExcept((byte)0b10101010));
+
+            NativeMemory.AlignedFree(ptr);
+        }
+
+        [Theory]
+        [InlineData(0)]
+        [InlineData(1)]
+        [InlineData(167)]
+        public void ZeroMemoryWithSizeEqualTo0ShouldNoOpTest(int offset)
+        {
+            byte* ptr = (byte*)NativeMemory.AlignedAlloc(512, 8);
+
+            Assert.True(ptr != null);
+            Assert.True((nuint)ptr % 8 == 0);
+
+            new Span<byte>(ptr, 512).Fill(0b10101010);
+
+            NativeMemory.ZeroMemory(ptr + offset, 0);
+
+            Assert.Equal(-1, new Span<byte>(ptr, 512).IndexOfAnyExcept((byte)0b10101010));
+
+            NativeMemory.AlignedFree(ptr);
+        }
+
+        [Fact]
+        public void ZeroMemoryWithNullPointerAndZeroByteCountTest()
+        {
+            NativeMemory.ZeroMemory(null, 0);
+
+            // This test method just needs to check that no exceptions are thrown
+        }
     }
 }