在.NET Micro Framework中将'float'转换为'byte [4]'并返回'float'

Question

将a转换float为a byte[4]然后再转换为'float' 的最佳方法是什么？

我在C#.NET Micro Framework中这样做,所以没有BitConverter我可以使用的.

Answer 1

转换uint为float(和反转)也可以用"安全"代码完成(虽然我不知道这是否可以在NETMF上实现).

[StructLayout(LayoutKind.Explicit)]
struct UIntFloat
{       
    [FieldOffset(0)]
    public float FloatValue;

    [FieldOffset(0)]
    public uint IntValue;        
}

public static float ToSingle(byte[] value, int index)        
{           
    uint i = ToUInt32(value, index);            
    return ToSingle(i);
}

public static float ToSingle(uint value)
{
    UIntFloat uf = new UIntFloat();
    uf.IntValue = value;
    return uf.FloatValue;
}

Answer 2

我已经BitConverter从Netduino 实现修改了该类，以允许字节顺序规范（这不是“最好的方法”，但它有效）。如果通过网络发送字节数组，我会使用BigEndian. 只是提醒一下，unsafeNETMF 并未正式支持。

using System;
using System.Diagnostics;

namespace netduino
{
    public static class BitConverter
    {
        public static byte[] GetBytes(uint value)
        {
            return new byte[4] { 
                    (byte)(value & 0xFF), 
                    (byte)((value >> 8) & 0xFF), 
                    (byte)((value >> 16) & 0xFF), 
                    (byte)((value >> 24) & 0xFF) };
        }

        public static unsafe byte[] GetBytes(float value)
        {
            uint val = *((uint*)&value);
            return GetBytes(val);
        }

        public static unsafe byte[] GetBytes(float value, ByteOrder order)
        {
            byte[] bytes = GetBytes(value);
            if (order != ByteOrder.LittleEndian)
            {
                System.Array.Reverse(bytes);
            }
            return bytes;
        }

        public static uint ToUInt32(byte[] value, int index)
        {
            return (uint)(
                value[0 + index] << 0 |
                value[1 + index] << 8 |
                value[2 + index] << 16 |
                value[3 + index] << 24);
        }

        public static unsafe float ToSingle(byte[] value, int index)
        {
            uint i = ToUInt32(value, index);
            return *(((float*)&i));
        }

        public static unsafe float ToSingle(byte[] value, int index, ByteOrder order)
        {
            if (order != ByteOrder.LittleEndian)
            {
                System.Array.Reverse(value, index, value.Length);
            }
            return ToSingle(value, index);
        }

        public enum ByteOrder
        {
            LittleEndian,
            BigEndian
        }

        static public bool IsLittleEndian
        {
            get
            {
                unsafe
                {
                    int i = 1;
                    char* p = (char*)&i;

                    return (p[0] == 1);
                }
            }
        }
    }
}

namespace BitConverterTest
{
    class Program
    {
        static void Main(string[] args)
        {
            byte[] msbFirst = new byte[] { 0x42, 0xF6, 0xE9, 0xE0 };
            byte[] lsbFirst = new byte[] { 0xE0, 0xE9, 0xF6, 0x42 };
            const float f = 123.456789F;

            byte[] b = netduino.BitConverter.GetBytes(f, netduino.BitConverter.ByteOrder.BigEndian);
            for (int i = 0; i < b.Length; i++)
            {
                Debug.Assert(msbFirst[i] == b[i], "BitConverter.GetBytes(float, BigEndian) i=" + i);
            }

            Debug.Assert(f == netduino.BitConverter.ToSingle(msbFirst, 0, netduino.BitConverter.ByteOrder.BigEndian));

            Console.WriteLine("All tests passed");
            Console.ReadKey();
        }
    }
}