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Fix potential endianness and alignment problems with Span-based UnicodeTrie constructor #284

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Merged
JimBobSquarePants merged 1 commit into from
Jun 30, 2022
Merged

Fix potential endianness and alignment problems with Span-based UnicodeTrie constructor #284

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47 changes: 22 additions & 25 deletions src/SixLabors.Fonts/Unicode/UnicodeTrie.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
// Licensed under the Apache License, Version 2.0.

using System;
using System.Buffers.Binary;
using System.IO;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
Expand All @@ -23,11 +24,26 @@ internal sealed class UnicodeTrie

public UnicodeTrie(ReadOnlySpan<byte> rawData)
{
var header = UnicodeTrieHeader.Parse(rawData);
var header = MemoryMarshal.Read<UnicodeTrieHeader>(rawData);

if (!BitConverter.IsLittleEndian)
{
header.HighStart = BinaryPrimitives.ReverseEndianness(header.HighStart);
header.ErrorValue = BinaryPrimitives.ReverseEndianness(header.ErrorValue);
header.DataLength = BinaryPrimitives.ReverseEndianness(header.DataLength);
}

int length = header.DataLength;
uint[] data = new uint[length / sizeof(uint)];
MemoryMarshal.Cast<byte, uint>(rawData.Slice(rawData.Length - length))
.CopyTo(data);
rawData.Slice(rawData.Length - length).CopyTo(MemoryMarshal.AsBytes(data.AsSpan()));

if (!BitConverter.IsLittleEndian)
{
for (int i = 0; i < data.Length; i++)
{
data[i] = BinaryPrimitives.ReverseEndianness(data[i]);
}
}

this.highStart = header.HighStart;
this.errorValue = header.ErrorValue;
Expand Down Expand Up @@ -149,30 +165,11 @@ public void Save(Stream stream)
}
}

[StructLayout(LayoutKind.Sequential, Pack = 1)]
private struct UnicodeTrieHeader
{
public int HighStart
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get;
}

public uint ErrorValue
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get;
}

public int DataLength
{
[MethodImpl(MethodImplOptions.AggressiveInlining)]
get;
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static UnicodeTrieHeader Parse(ReadOnlySpan<byte> data)
=> MemoryMarshal.Cast<byte, UnicodeTrieHeader>(data)[0];
public int HighStart;
public uint ErrorValue;
public int DataLength;
}
}
}