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Make FNV hash compatible across endianness #9489

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Make FNV hash compatible across endianness #9489

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21 changes: 3 additions & 18 deletions src/StringTools/FowlerNollVo1aHash.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,6 @@ public static int ComputeHash32(string text)
{
uint hash = fnvOffsetBasisA32Bit;

#if NET35
unchecked
{
for (int i = 0; i < text.Length; i++)
Expand All @@ -48,20 +47,14 @@ public static int ComputeHash32(string text)
hash *= fnvPrimeA32Bit;
}
}
#else
ReadOnlySpan<byte> span = MemoryMarshal.Cast<char, byte>(text.AsSpan());
foreach (byte b in span)
{
hash = unchecked((hash ^ b) * fnvPrimeA32Bit);
}
#endif

return unchecked((int)hash);
}

/// <summary>
/// Computes 64 bit Fowler/Noll/Vo-1a hash optimized for ASCII strings.
/// The hashing algorithm considers only the first 8 bits of each character.
/// Computes 64 bit Fowler/Noll/Vo-1a inspired hash of a string.
/// The hashing algorithm process the data by the whole 16bit chars, instead of by bytes.
/// this speeds up the hashing process almost by 2x, while not significantly increasing collisions rate.
/// Analysis: https://github.com/KirillOsenkov/MSBuildStructuredLog/wiki/String-Hashing#faster-fnv-1a
/// </summary>
/// <param name="text">String to be hashed.</param>
Expand Down Expand Up @@ -92,7 +85,6 @@ public static long ComputeHash64(string text)
{
long hash = fnvOffsetBasisA64Bit;

#if NET35
unchecked
{
for (int i = 0; i < text.Length; i++)
Expand All @@ -107,13 +99,6 @@ public static long ComputeHash64(string text)
hash *= fnvPrimeA64Bit;
}
}
#else
ReadOnlySpan<byte> span = MemoryMarshal.Cast<char, byte>(text.AsSpan());
foreach (byte b in span)
{
hash = unchecked((hash ^ b) * fnvPrimeA64Bit);
}
#endif

return hash;
}
Expand Down