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Use safe Span.Slice loop pattern in CRC32 ARM scalar paths #127386

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Merged
EgorBo merged 2 commits into from
Apr 24, 2026
+20 −41
Merged

Use safe Span.Slice loop pattern in CRC32 ARM scalar paths #127386

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7d1ad32
Use safe Span.Slice loop pattern in CRC32 ARM scalar paths
EgorBo Apr 24, 2026
32a1c70
Update src/libraries/System.IO.Hashing/src/System/IO/Hashing/Crc32Par…
EgorBo Apr 24, 2026
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61 changes: 20 additions & 41 deletions src/libraries/System.IO.Hashing/src/System/IO/Hashing/Crc32ParameterSet.WellKnown.cs
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Original file line number Diff line number Diff line change
@@ -1,8 +1,10 @@
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

#if NET
using System.Buffers.Binary;
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#endif
using System.Diagnostics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace System.IO.Hashing
Expand Down Expand Up @@ -133,20 +135,12 @@ private static uint UpdateScalarArm64(uint crc, ReadOnlySpan<byte> source)
Debug.Assert(System.Runtime.Intrinsics.Arm.Crc32.Arm64.IsSupported, "ARM CRC support is required.");

// Compute in 8 byte chunks
if (source.Length >= sizeof(ulong))
while (source.Length >= sizeof(ulong))
{
ref byte ptr = ref MemoryMarshal.GetReference(source);

// Exclude trailing bytes not a multiple of 8
int longLength = source.Length & ~0x7;

for (int i = 0; i < longLength; i += sizeof(ulong))
{
crc = System.Runtime.Intrinsics.Arm.Crc32.Arm64.ComputeCrc32(
crc,
Unsafe.ReadUnaligned<ulong>(ref Unsafe.Add(ref ptr, i)));
}
source = source.Slice(longLength);
crc = System.Runtime.Intrinsics.Arm.Crc32.Arm64.ComputeCrc32(
crc,
BinaryPrimitives.ReadUInt64LittleEndian(source));
source = source.Slice(sizeof(ulong));
}

// Compute remaining bytes
Expand All @@ -163,21 +157,12 @@ private static uint UpdateScalarArm(uint crc, ReadOnlySpan<byte> source)
Debug.Assert(System.Runtime.Intrinsics.Arm.Crc32.IsSupported, "ARM CRC support is required.");

// Compute in 4 byte chunks
if (source.Length >= sizeof(uint))
while (source.Length >= sizeof(uint))
{
ref byte ptr = ref MemoryMarshal.GetReference(source);

// Exclude trailing bytes not a multiple of 4
int intLength = source.Length & ~0x3;

for (int i = 0; i < intLength; i += sizeof(uint))
{
crc = System.Runtime.Intrinsics.Arm.Crc32.ComputeCrc32(
crc,
Unsafe.ReadUnaligned<uint>(ref Unsafe.Add(ref ptr, i)));
}

source = source.Slice(intLength);
crc = System.Runtime.Intrinsics.Arm.Crc32.ComputeCrc32(
crc,
BinaryPrimitives.ReadUInt32LittleEndian(source));
source = source.Slice(sizeof(uint));
}

// Compute remaining bytes
Expand Down Expand Up @@ -243,33 +228,27 @@ private static uint UpdateIntrinsic(uint crc, ReadOnlySpan<byte> source)
else
{
Debug.Assert(System.Runtime.Intrinsics.Arm.Crc32.IsSupported);
ref byte ptr = ref MemoryMarshal.GetReference(source);
int offset = 0;

if (System.Runtime.Intrinsics.Arm.Crc32.Arm64.IsSupported)
{
int longLength = source.Length & ~0x7; // Exclude trailing bytes not a multiple of 8

for (; offset < longLength; offset += sizeof(ulong))
while (source.Length >= sizeof(ulong))
{
crc = System.Runtime.Intrinsics.Arm.Crc32.Arm64.ComputeCrc32C(
crc,
Unsafe.ReadUnaligned<ulong>(ref Unsafe.Add(ref ptr, offset)));
BinaryPrimitives.ReadUInt64LittleEndian(source));
source = source.Slice(sizeof(ulong));
}
}

int intLength = source.Length & ~0x3; // Exclude trailing bytes not a multiple of 4

for (; offset < intLength; offset += sizeof(uint))
while (source.Length >= sizeof(uint))
{
crc = System.Runtime.Intrinsics.Arm.Crc32.ComputeCrc32C(
crc,
Unsafe.ReadUnaligned<uint>(ref Unsafe.Add(ref ptr, offset)));
BinaryPrimitives.ReadUInt32LittleEndian(source));
source = source.Slice(sizeof(uint));
}

ReadOnlySpan<byte> remainingBytes = source.Slice(offset);

foreach (byte value in remainingBytes)
foreach (byte value in source)
{
crc = System.Runtime.Intrinsics.Arm.Crc32.ComputeCrc32C(crc, value);
}
Expand Down
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