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Tweak Tiktoken's BytePairEncode for improved perf #7017

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Feb 20, 2024
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Tweak Tiktoken's BytePairEncode for improved perf #7017

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54 changes: 37 additions & 17 deletions src/Microsoft.ML.Tokenizers/Utils/BytePairEncoder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
// See the LICENSE file in the project root for more information.

using System;
using System.Buffers;
using System.Collections.Generic;

namespace Microsoft.ML.Tokenizers
Expand All @@ -19,63 +20,82 @@ public static int[] BytePairEncode(ReadOnlyMemory<byte> mergingBytes, Dictionary
return [ranks[mergingBytes]];
}

var byteIndicesAndRanks = new List<(int Index, int Rank)>();
for (int i = 0; i < mergingBytes.Length + 1; i++)
(int Index, int Rank)[]? arrayPoolArray = null;
int requiredLength = mergingBytes.Length + 1;
Span<(int Index, int Rank)> byteIndicesAndRanks = requiredLength <= 64 ?
stackalloc (int, int)[64] :
(arrayPoolArray = ArrayPool<(int, int)>.Shared.Rent(requiredLength));
byteIndicesAndRanks = byteIndicesAndRanks.Slice(0, requiredLength);

for (int i = 0; i < byteIndicesAndRanks.Length; i++)
{
byteIndicesAndRanks.Add((i, int.MaxValue));
byteIndicesAndRanks[i] = (i, int.MaxValue);
}
int GetRank(int startIndex, int skip = 0)

int GetRank(Span<(int Index, int Rank)> byteIndicesAndRanks, int startIndex, int skip = 0)
{
if (startIndex + skip + 2 < byteIndicesAndRanks.Count)
if (startIndex + skip + 2 < byteIndicesAndRanks.Length)
{
var slice = mergingBytes.SliceStartEnd(byteIndicesAndRanks[startIndex].Index, byteIndicesAndRanks[startIndex + skip + 2].Index);
if (ranks.TryGetValue(slice, out var rank))
{
return rank;
}
}

return int.MaxValue;
}
for (int i = 0; i < byteIndicesAndRanks.Count - 2; i++)

for (int i = 0; i < byteIndicesAndRanks.Length - 2; i++)
{
var rank = GetRank(i);
int rank = GetRank(byteIndicesAndRanks, i);
if (rank != int.MaxValue)
{
byteIndicesAndRanks[i] = (byteIndicesAndRanks[i].Index, rank);
byteIndicesAndRanks[i].Rank = rank;
}
}
while (byteIndicesAndRanks.Count > 1)

while (byteIndicesAndRanks.Length > 1)
{
var minRank = (Index: 0, Rank: int.MaxValue);
for (int i = 0; i < byteIndicesAndRanks.Count - 1; i++)
for (int i = 0; i < byteIndicesAndRanks.Length - 1; i++)
{
if (byteIndicesAndRanks[i].Rank < minRank.Rank)
{
minRank = (i, byteIndicesAndRanks[i].Rank);
}
}

if (minRank.Rank != int.MaxValue)
{
int j = minRank.Index;
byteIndicesAndRanks[j] = (byteIndicesAndRanks[j].Index, GetRank(j, 1));
byteIndicesAndRanks[j].Rank = GetRank(byteIndicesAndRanks, j, 1);
if (j > 0)
{
byteIndicesAndRanks[j - 1] = (byteIndicesAndRanks[j - 1].Index, GetRank(j - 1, 1));
byteIndicesAndRanks[j - 1].Rank = GetRank(byteIndicesAndRanks, j - 1, 1);
}
byteIndicesAndRanks.RemoveAt(j + 1);

byteIndicesAndRanks.Slice(j + 2).CopyTo(byteIndicesAndRanks.Slice(j + 1));
byteIndicesAndRanks = byteIndicesAndRanks.Slice(0, byteIndicesAndRanks.Length - 1);
}
else
{
break;
}
}

var outList = new int[byteIndicesAndRanks.Count - 1];
for (int i = 0; i < byteIndicesAndRanks.Count - 1; i++)
var result = new int[byteIndicesAndRanks.Length - 1];
for (int i = 0; i < result.Length; i++)
{
outList[i] = ranks[mergingBytes.SliceStartEnd(byteIndicesAndRanks[i].Index, byteIndicesAndRanks[i + 1].Index)];
result[i] = ranks[mergingBytes.SliceStartEnd(byteIndicesAndRanks[i].Index, byteIndicesAndRanks[i + 1].Index)];
}
return outList;

if (arrayPoolArray is not null)
{
ArrayPool<(int, int)>.Shared.Return(arrayPoolArray);
}

return result;
}

private static ReadOnlyMemory<byte> SliceStartEnd(this ReadOnlyMemory<byte> memory, int start, int end) => memory.Slice(start, end - start);
Expand Down