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Add Big Endian Support for Float32 in BinaryVectorWriter.WriteToBytes<T>() #1682

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ff89368
Add Big Endian Support for Float32 in BinaryVectorWriter.WriteToBytes…
May 5, 2025
2c2cae1
Added comments for clarity
medhatiwari May 6, 2025
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27 changes: 19 additions & 8 deletions src/MongoDB.Bson/Serialization/BinaryVectorReader.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
*/

using System;
using System.Buffers.Binary;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
Expand All @@ -26,7 +27,6 @@ public static BinaryVector<TItem> ReadBinaryVector<TItem>(ReadOnlyMemory<byte> v
where TItem : struct
{
var (items, padding, vectorDataType) = ReadBinaryVectorAsArray<TItem>(vectorData);

return CreateBinaryVector(items, padding, vectorDataType);
}

Expand All @@ -41,29 +41,39 @@ public static (TItem[] Items, byte Padding, BinaryVectorDataType VectorDataType)
switch (vectorDataType)
{
case BinaryVectorDataType.Float32:

if ((vectorDataBytes.Span.Length & 3) != 0)
{
throw new FormatException("Data length of binary vector of type Float32 must be a multiple of 4 bytes.");
}

if (BitConverter.IsLittleEndian)
if (typeof(TItem) != typeof(float))
{
var singles = MemoryMarshal.Cast<byte, float>(vectorDataBytes.Span);
items = (TItem[])(object)singles.ToArray();
throw new NotSupportedException($"Expected float for Float32 vector type, but found {typeof(TItem)}.");
}
else

int count = vectorDataBytes.Length / 4; // 4 bytes per float
float[] floatArray = new float[count];

for (int i = 0; i < count; i++)
{
throw new NotSupportedException("Binary vector data is not supported on Big Endian architecture yet.");
// Each float32 is 4 bytes. So to extract the i-th float, we slice 4 bytes from offset i * 4. Use little-endian or big-endian decoding based on platform.
floatArray[i] = BitConverter.IsLittleEndian
? MemoryMarshal.Read<float>(vectorDataBytes.Span.Slice(i * 4, 4)) // fast, unaligned read on little endian
: BinaryPrimitives.ReadSingleBigEndian(vectorDataBytes.Span.Slice(i * 4, 4)); // correctly reassemble 4 bytes as big-endian float
}

items = (TItem[])(object)floatArray;
break;

case BinaryVectorDataType.Int8:
var itemsSpan = MemoryMarshal.Cast<byte, TItem>(vectorDataBytes.Span);
items = (TItem[])(object)itemsSpan.ToArray();
items = itemsSpan.ToArray();
break;

case BinaryVectorDataType.PackedBit:
items = (TItem[])(object)vectorDataBytes.ToArray();
break;

default:
throw new NotSupportedException($"Binary vector data type {vectorDataType} is not supported.");
}
Expand Down Expand Up @@ -149,3 +159,4 @@ private static void ValidateItemTypeForBinaryVector<TItem, TItemExpectedType, TB
}
}
}

40 changes: 35 additions & 5 deletions src/MongoDB.Bson/Serialization/BinaryVectorWriter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
*/

using System;
using System.Buffers.Binary;
using System.Runtime.InteropServices;

namespace MongoDB.Bson.Serialization
Expand All @@ -35,15 +36,44 @@ public static byte[] WriteToBytes<TItem>(BinaryVector<TItem> binaryVector)
public static byte[] WriteToBytes<TItem>(ReadOnlySpan<TItem> vectorData, BinaryVectorDataType binaryVectorDataType, byte padding)
where TItem : struct
{
if (!BitConverter.IsLittleEndian)
if (BitConverter.IsLittleEndian)
{
throw new NotSupportedException("Binary vector data is not supported on Big Endian architecture yet.");
var vectorDataBytes = MemoryMarshal.Cast<TItem, byte>(vectorData);
byte[] result = [(byte)binaryVectorDataType, padding, .. vectorDataBytes];
return result;
}

var vectorDataBytes = MemoryMarshal.Cast<TItem, byte>(vectorData);
byte[] result = [(byte)binaryVectorDataType, padding, .. vectorDataBytes];
byte[] resultBytes;
switch (binaryVectorDataType)
{
case BinaryVectorDataType.Float32:
int length = vectorData.Length * sizeof(float);
resultBytes = new byte[2 + length]; // Allocate output buffer:
resultBytes[0] = (byte)binaryVectorDataType; // - [0]: vector type
resultBytes[1] = padding; // - [1]: padding
var floatSpan = MemoryMarshal.Cast<TItem, float>(vectorData);
Span<byte> floatOutput = resultBytes.AsSpan(2); // - [2...]: actual float data , skipping header
foreach (var value in floatSpan)
{
// Each float is 4 bytes - write in Big Endian format
BinaryPrimitives.WriteSingleBigEndian(floatOutput, value);
floatOutput = floatOutput.Slice(4); // advance to next 4-byte block
}
return resultBytes;

case BinaryVectorDataType.Int8:
case BinaryVectorDataType.PackedBit:
var vectorDataBytes = MemoryMarshal.Cast<TItem, byte>(vectorData);
resultBytes = new byte[2 + vectorDataBytes.Length];
resultBytes[0] = (byte)binaryVectorDataType;
resultBytes[1] = padding;
vectorDataBytes.CopyTo(resultBytes.AsSpan(2));
return resultBytes;

return result;
default:
throw new NotSupportedException($"Binary vector serialization is not supported for {binaryVectorDataType} on Big Endian architecture yet.");
}
}
}
}