A hack to temporarily view a float array as a byte array and vice versa, in O(1) - without mem copy. License: FreeBSD

FastArraySerializer.cs

/*
Copyright (c) 2013, Omer Mor
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met: 

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer. 
2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution. 

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those
of the authors and should not be interpreted as representing official policies, 
either expressed or implied, of the FreeBSD Project
*/

using System;
using System.Runtime.InteropServices;

namespace OmerMor.Utils
{
    public static unsafe class FastArraySerializer
    {
        [StructLayout(LayoutKind.Explicit)]
        private struct Union
        {
            [FieldOffset(0)] public byte[] bytes;
            [FieldOffset(0)] public float[] floats;
        }

        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        private struct ArrayHeader
        {
            public UIntPtr type;
            public UIntPtr length;
        }

        private static readonly UIntPtr BYTE_ARRAY_TYPE;
        private static readonly UIntPtr FLOAT_ARRAY_TYPE;

        static FastArraySerializer()
        {
            fixed (void* pBytes = new byte[1])
            fixed (void* pFloats = new float[1])
            {
                BYTE_ARRAY_TYPE = getHeader(pBytes)->type;
                FLOAT_ARRAY_TYPE = getHeader(pFloats)->type;
            }
        }

        public static void AsByteArray(this float[] floats, Action<byte[]> action)
        {
            if (floats.handleNullOrEmptyArray(action)) 
                return;

            var union = new Union {floats = floats};
            union.floats.toByteArray();
            try
            {
                action(union.bytes);
            }
            finally
            {
                union.bytes.toFloatArray();
            }
        }

        public static void AsFloatArray(this byte[] bytes, Action<float[]> action)
        {
            if (bytes.handleNullOrEmptyArray(action)) 
                return;

            var union = new Union {bytes = bytes};
            union.bytes.toFloatArray();
            try
            {
                action(union.floats);
            }
            finally
            {
                union.floats.toByteArray();
            }
        }

        public static bool handleNullOrEmptyArray<TSrc,TDst>(this TSrc[] array, Action<TDst[]> action)
        {
            if (array == null)
            {
                action(null);
                return true;
            }

            if (array.Length == 0)
            {
                action(new TDst[0]);
                return true;
            }

            return false;
        }

        private static ArrayHeader* getHeader(void* pBytes)
        {
            return (ArrayHeader*)pBytes - 1;
        }

        private static void toFloatArray(this byte[] bytes)
        {
            fixed (void* pArray = bytes)
            {
                var pHeader = getHeader(pArray);

                pHeader->type = FLOAT_ARRAY_TYPE;
                pHeader->length = (UIntPtr)(bytes.Length / sizeof(float));
            }
        }

        private static void toByteArray(this float[] floats)
        {
            fixed(void* pArray = floats)
            {
                var pHeader = getHeader(pArray);

                pHeader->type = BYTE_ARRAY_TYPE;
                pHeader->length = (UIntPtr)(floats.Length * sizeof(float));
            }
        }
    }
}

FastArraySerializerTester.cs

/*
Copyright (c) 2013, Omer Mor
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met: 

1. Redistributions of source code must retain the above copyright notice, this
   list of conditions and the following disclaimer. 
2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution. 

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those
of the authors and should not be interpreted as representing official policies, 
either expressed or implied, of the FreeBSD Project
*/

using System;
using System.Linq;

namespace OmerMor.Utils
{
    public class FastArraySerializerTester
    {
        public static void Main()
        {
            Floats_to_bytes_and_vice_versa();
        }

        public static void Floats_to_bytes_and_vice_versa()
        {
            var floats = Enumerable.Range(0, 500).Select(i => (float)i).ToArray();

            var floatsClone = new float[] {};
            var bytes = new byte[] {};
            
            floats.AsByteArray(arr =>
            {
                bytes = new byte[arr.Length];
                Array.Copy(arr, bytes, arr.Length);
            });
            
            bytes.AsFloatArray(arr =>
            {
                floatsClone = new float[arr.Length];
                Array.Copy(arr, floatsClone, arr.Length);
            });
            
            var areEqual = floats.SequenceEqual(floatsClone);
            if (!areEqual)
                throw new ApplicationException("Arrays do not match");
        }
    }
}

Thanks @jkotas & @HelloKitty !
I guess pinning the array for the entire span of the function would guard against this corruption.
What do you think?