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

src/MongoDB.Bson/Serialization/BinaryVectorReader.cs

@@ -14,6 +14,7 @@
 */
 
 using System;
+using System.Buffers.Binary;
 using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
@@ -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);
         }
 
@@ -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.");
             }
@@ -149,3 +159,4 @@ private static void ValidateItemTypeForBinaryVector<TItem, TItemExpectedType, TB
         }
     }
 }
+

src/MongoDB.Bson/Serialization/BinaryVectorWriter.cs

@@ -14,6 +14,7 @@
 */
 
 using System;
+using System.Buffers.Binary;
 using System.Runtime.InteropServices;
 
 namespace MongoDB.Bson.Serialization
@@ -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.");
+            }
         }
     }
 }
+