标签：
那么，我们写个程序来测试一下吧。下面就是 BitConverterTester.cs：
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using System;namespace Skyiv.Tester{ static class BitConverterTester { static void Main() { Console.WriteLine("
OS Version: " +
Environment.OSVersion); Console.WriteLine("
CLR Version: " +
Environment.Version); Console.WriteLine("
IsLittleEndian: " +
BitConverter.IsLittleEndian); long n
= 0x1234567890ABCDEF; double d
= 1; Console.WriteLine(n.ToString("X")
+ ":
" +
BitConverter.ToString(BitConverter.GetBytes(n))); Console.WriteLine(d.ToString("F14")
+ ":
" +
BitConverter.ToString(BitConverter.GetBytes(d))); } }} |
这个程序在 Windows Server 2003 操作系统的 .NET Framework 4 环境下编译和运行：
C:\CS\BitConverterTester> csc BitConverterTester.cs
Microsoft(R) Visual C# 2010 编译器 4.0.30319.1 版
版权所有(C) Microsoft Corporation。保留所有权利。
C:\CS\BitConverterTester> BitConverterTester
OS Version: Microsoft Windows NT 5.2.3790 Service Pack 2
CLR Version: 4.0.30319.1
IsLittleEndian: True
1234567890ABCDEF: EF-CD-AB-90-78-56-34-12
1.00000000000000: 00-00-00-00-00-00-F0-3F
C:\CS\BitConverterTester>
在 Ubuntu 10.10 操作系统的 Mono 2.8.2 环境下编译和运行：
ben@ben-m4000t:~/work/BitConverterTester$ dmcs BitConverterTester.cs
ben@ben-m4000t:~/work/BitConverterTester$ mono28 BitConverterTester.exe
OS Version: Unix 2.6.35.24
CLR Version: 4.0.30319.1
IsLittleEndian: True
1234567890ABCDEF: EF-CD-AB-90-78-56-34-12
1.00000000000000: 00-00-00-00-00-00-F0-3F
ben@ben-m4000t:~/work/BitConverterTester$
这两次运行的结果都在预料之中，BitConverter 类的 GetBytes 方法以 Little-Endian 顺序返回字节数组。但是，在这两次运行中，IsLittleEndian 的值都为 True，所以还是没有解决我们的问题。
祭出 Reflector 这个神器：
在 mscorlib.dll 的 System 命名空间下找到 BitConverter 类:
如上图如示，IsLittleEndian 是 BitConverter 类的静态只读字段。
如上图所示，在 BitConverter 类的静态构造函数中，直接把 IsLittleEndian 这个静态只读字段的值赋值为 true。由于我没有 Microsoft 实现 BitConverter 类的 C# 源程序代码，不知道是 Microsoft 的 C# 源程序中就是直接这样写呢，还是实际上是有根据平台来判断的，但是 C# 编译器在具体平台上优化了这段代码。
如上图所示，GetBytes(Int64) 方法也非常简单，直接通过不安全的指针转换就得到了相应的字节数组。学过 C 语言中的朋友想必非常熟悉这种做法。这下清楚了，BitConverter 类的 GetBytes 方法是根据 IsLittleEndian 的值的不同按照不同顺序来返回字节数组的。MSDN 文档在“BigInteger 构造函数 (Byte[]) ”中的相关说法：“例如 BigInteger.ToByteArray 和 BitConverter.GetBytes，以 little-endian 顺序返回字节数组”是不正确的。
继续看下去：
上图中的 ToInt64 方法也明确地根据 IsLittleEndian 的值采取不同的动作。其实，既然在静态构造函数中明确地给 IsLittleEndian 赋值为 true，这里也可以省略对 IsLittleEndian 的判断，直接按照 IsLittleEndian 的值为 true 去做就行了，可以稍微节省点代码，提高点速度。
我们看到，GetBytes(Double) 方法也非常简单。
我们可以到 http://ftp.novell.com/pub/mono/sources/mono/ 下载 Mono 的源代码，然后按以下方法找到 BitConverter 类的源程序代码：
ben@ben-m4000t:~$ cd src/mono-2.8.2 ben@ben-m4000t:~/src/mono-2.8.2$ find . -name BitConverter.cs ./mcs/class/corlib/System/BitConverter.cs ben@ben-m4000t:~/src/mono-2.8.2$
下面就是 BitConverter.cs：
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////
System.BitConverter.cs////
Author://
Matt Kimball (matt@kimball.net)//////
Copyright (C) 2004 Novell, Inc (http://www.novell.com)////
Permission is hereby granted, free of charge, to any person obtaining//
a copy of this software and associated documentation files (the//
"Software"), to deal in the Software without restriction, including//
without limitation the rights to use, copy, modify, merge, publish,//
distribute, sublicense, and/or sell copies of the Software, and to//
permit persons to whom the Software is furnished to do so, subject to//
the following conditions://
//
The above copyright notice and this permission notice shall be//
included in all copies or substantial portions of the Software.//
//
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,//
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF//
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND//
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE//
LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION//
OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION//
WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.//using System.Text;namespace System{ public static class BitConverter { static readonly bool SwappedWordsInDouble
= DoubleWordsAreSwapped (); public static readonly bool IsLittleEndian
= AmILittleEndian (); static unsafe bool AmILittleEndian
() { //
binary representations of 1.0: //
big endian: 3f f0 00 00 00 00 00 00 //
little endian: 00 00 00 00 00 00 f0 3f //
arm fpa little endian: 00 00 f0 3f 00 00 00 00 double d
= 1.0; byte *b
= (byte*)&d; return (b
[0] == 0); } static unsafe bool DoubleWordsAreSwapped
() { //
binary representations of 1.0: //
big endian: 3f f0 00 00 00 00 00 00 //
little endian: 00 00 00 00 00 00 f0 3f //
arm fpa little endian: 00 00 f0 3f 00 00 00 00 double d
= 1.0; byte *b
= (byte*)&d; return b
[2] == 0xf0; } public static long DoubleToInt64Bits
(double value) { return ToInt64
(GetBytes (value), 0); } public static double Int64BitsToDouble
(long value) { return ToDouble
(GetBytes (value), 0); } internal static double InternalInt64BitsToDouble
(long value) { return SwappableToDouble
(GetBytes (value), 0); } unsafe static byte[]
GetBytes (byte *ptr,
int count) { byte []
ret = new byte [count]; for (int i
= 0; i < count; i++) { ret
[i] = ptr [i]; } return ret; } unsafe public static byte[]
GetBytes (bool value) { return GetBytes
((byte *)
&value, 1); } unsafe public static byte[]
GetBytes (char value) { return GetBytes
((byte *)
&value, 2); } unsafe public static byte[]
GetBytes (short value) { return GetBytes
((byte *)
&value, 2); } unsafe public static byte[]
GetBytes (int value) { return GetBytes
((byte *)
&value, 4); } unsafe public static byte[]
GetBytes (long value) { return GetBytes
((byte *)
&value, 8); } [CLSCompliant
(false)] unsafe public static byte[]
GetBytes (ushort value) { return GetBytes
((byte *)
&value, 2); } [CLSCompliant
(false)] unsafe public static byte[]
GetBytes (uint value) { return GetBytes
((byte *)
&value, 4); } [CLSCompliant
(false)] unsafe public static byte[]
GetBytes (ulong value) { return GetBytes
((byte *)
&value, 8); } unsafe public static byte[]
GetBytes (float value) { return GetBytes
((byte *)
&value, 4); } unsafe public static byte[]
GetBytes (double value) { if (SwappedWordsInDouble)
{ byte[]
data = new byte [8]; byte *p
= (byte*)&value; data
[0] = p [4]; data
[1] = p [5]; data
[2] = p [6]; data
[3] = p [7]; data
[4] = p [0]; data
[5] = p [1]; data
[6] = p [2]; data
[7] = p [3]; return data; }
else { return GetBytes
((byte *)
&value, 8); } } unsafe static void PutBytes
(byte *dst,
byte[]
src, int start_index,
int count) { if (src
== null) throw new ArgumentNullException
("value"); if (start_index
< 0 || (start_index > src.Length - 1)) throw new ArgumentOutOfRangeException
("startIndex",
"Index
was" +
"
out of range. Must be non-negative and less than the" +
"
size of the collection."); //
avoid integer overflow (with large pos/neg start_index values) if (src.Length
- count < start_index) throw new ArgumentException
("Destination
array is not long" +
"
enough to copy all the items in the collection." +
"
Check array index and length."); for (int i
= 0; i < count; i++) dst[i]
= src[i + start_index]; } unsafe public static bool ToBoolean
(byte[]
value, int startIndex) { if (value
== null)
throw new ArgumentNullException
("value"); if (startIndex
< 0 || (startIndex > value.Length - 1)) throw new ArgumentOutOfRangeException
("startIndex",
"Index
was" +
"
out of range. Must be non-negative and less than the" +
"
size of the collection."); if (value
[startIndex] != 0) return true; return false; } unsafe public static char ToChar
(byte[]
value, int startIndex) { char ret; PutBytes
((byte *)
&ret, value, startIndex, 2); return ret; } unsafe public static short ToInt16
(byte[]
value, int startIndex) { short ret; PutBytes
((byte *)
&ret, value, startIndex, 2); return ret; } unsafe public static int ToInt32
(byte[]
value, int startIndex) { int ret; PutBytes
((byte *)
&ret, value, startIndex, 4); return ret; } unsafe public static long ToInt64
(byte[]
value, int startIndex) { long ret; PutBytes
((byte *)
&ret, value, startIndex, 8); return ret; } [CLSCompliant
(false)] unsafe public static ushort ToUInt16
(byte[]
value, int startIndex) { ushort ret; PutBytes
((byte *)
&ret, value, startIndex, 2); return ret; } [CLSCompliant
(false)] unsafe public static uint ToUInt32
(byte[]
value, int startIndex) { uint ret; PutBytes
((byte *)
&ret, value, startIndex, 4); return ret; } [CLSCompliant
(false)] unsafe public static ulong ToUInt64
(byte[]
value, int startIndex) { ulong ret; PutBytes
((byte *)
&ret, value, startIndex, 8); return ret; } unsafe public static float ToSingle
(byte[]
value, int startIndex) { float ret; PutBytes
((byte *)
&ret, value, startIndex, 4); return ret; } unsafe public static double ToDouble
(byte[]
value, int startIndex) { double ret; if (SwappedWordsInDouble)
{ byte*
p = (byte*)&ret; if (value
== null) throw new ArgumentNullException
("value"); if (startIndex
< 0 || (startIndex > value.Length - 1)) throw new ArgumentOutOfRangeException
("startIndex",
"Index
was" +
"
out of range. Must be non-negative and less than the" +
"
size of the collection."); //
avoid integer overflow (with large pos/neg start_index values) if (value.Length
- 8 < startIndex) throw new ArgumentException
("Destination
array is not long" +
"
enough to copy all the items in the collection." +
"
Check array index and length."); p
[0] = value [startIndex + 4]; p
[1] = value [startIndex + 5]; p
[2] = value [startIndex + 6]; p
[3] = value [startIndex + 7]; p
[4] = value [startIndex + 0]; p
[5] = value [startIndex + 1]; p
[6] = value [startIndex + 2]; p
[7] = value [startIndex + 3]; return ret; } PutBytes
((byte *)
&ret, value, startIndex, 8); return ret; } unsafe internal static double SwappableToDouble
(byte[]
value, int startIndex) { double ret; if (SwappedWordsInDouble)
{ byte*
p = (byte*)&ret; if (value
== null) throw new ArgumentNullException
("value"); if (startIndex
< 0 || (startIndex > value.Length - 1)) throw new ArgumentOutOfRangeException
("startIndex",
"Index
was" +
"
out of range. Must be non-negative and less than the" +
"
size of the collection."); //
avoid integer overflow (with large pos/neg start_index values) if (value.Length
- 8 < startIndex) throw new ArgumentException
("Destination
array is not long" +
"
enough to copy all the items in the collection." +
"
Check array index and length."); p
[0] = value [startIndex + 4]; p
[1] = value [startIndex + 5]; p
[2] = value [startIndex + 6]; p
[3] = value [startIndex + 7]; p
[4] = value [startIndex + 0]; p
[5] = value [startIndex + 1]; p
[6] = value [startIndex + 2]; p
[7] = value [startIndex + 3]; return ret; }
else if (!IsLittleEndian)
{ byte*
p = (byte*)&ret; if (value
== null) throw new ArgumentNullException
("value"); if (startIndex
< 0 || (startIndex > value.Length - 1)) throw new ArgumentOutOfRangeException
("startIndex",
"Index
was" +
"
out of range. Must be non-negative and less than the" +
"
size of the collection."); //
avoid integer overflow (with large pos/neg start_index values) if (value.Length
- 8 < startIndex) throw new ArgumentException
("Destination
array is not long" +
"
enough to copy all the items in the collection." +
"
Check array index and length."); p
[0] = value [startIndex + 7]; p
[1] = value [startIndex + 6]; p
[2] = value [startIndex + 5]; p
[3] = value [startIndex + 4]; p
[4] = value [startIndex + 3]; p
[5] = value [startIndex + 2]; p
[6] = value [startIndex + 1]; p
[7] = value [startIndex + 0]; return ret; } PutBytes
((byte *)
&ret, value, startIndex, 8); return ret; } public static string ToString
(byte[]
value) { if (value
== null) throw new ArgumentNullException
("value"); return ToString
(value, 0, value.Length); } public static string ToString
(byte[]
value, int startIndex) { if (value
== null) throw new ArgumentNullException
("value"); return ToString
(value, startIndex, value.Length - startIndex); } public static string ToString
(byte[]
value, int startIndex,
int length) { if (value
== null) throw new ArgumentNullException
("byteArray"); //
The 4th and last clause (start_index >= value.Length) //
was added as a small fix to a very obscure bug. //
It makes a small difference when start_index is //
outside the range and length==0. if (startIndex
< 0 || startIndex >= value.Length) { //
special (but valid) case (e.g. new byte [0]) if ((startIndex
== 0) && (value.Length == 0)) return String.Empty; throw new ArgumentOutOfRangeException
("startIndex",
"Index
was" +
"
out of range. Must be non-negative and less than the" +
"
size of the collection."); } if (length
< 0) throw new ArgumentOutOfRangeException
("length", "Value
must be positive."); //
note: re-ordered to avoid possible integer overflow if (startIndex
> value.Length - length) throw new ArgumentException
("startIndex
+ length > value.Length"); if (length
== 0) return string.Empty; StringBuilder
builder = new StringBuilder(length
* 3 - 1); int end
= startIndex + length; for (int i
= startIndex; i < end; i++) { if (i
> startIndex) builder.Append(‘-‘); char high
= (char)((value[i]
>> 4) & 0x0f); char low
= (char)(value[i]
& 0x0f); if (high
< 10) high
+= ‘0‘; else { high
-= (char)
10; high
+= ‘A‘; } if (low
< 10) low
+= ‘0‘; else { low
-= (char)
10; low
+= ‘A‘; } builder.Append(high); builder.Append(low); } return builder.ToString
(); } }} |
可以看出，在第 39 行通过第 41 到 50 行的 AmILittleEndian 方法给 IsLittleEndian 这个静态只读字段赋值。这个 AmILittleEndian 方法中的注释写得很明白，其实有三种不台的平台，除了 Big-Endian 和 Little-Endian 外，还有一种“arm fpa little endian”，在这里也归于 Little-Endian。但是在后面的方法中是要以不同的手段进行处理的。
另外，不象 Microsoft .NET Framework 4，Mono 中 BitConverter 类的各种重载的公有静态GetBytes 方法是统一调用第 78 到 87 行的私有静态 GetBytes 方法来实现其功能的。
从 Mono 中相关的源程序代码中也可以看出，BitConverter 类的 GetBytes 方法是根据 IsLittleEndian 的值的不同以不同的顺序返回字节数组的。
总结一下，MSDN 文档在“BigInteger 构造函数 (Byte[]) ”中的相关说法：“例如 BigInteger.ToByteArray 和 BitConverter.GetBytes，以 little-endian 顺序返回字节数组”是不正确的。BitConverter 类的 GetBytes 方法是根据 IsLittleEndian 的值的不同以不同的顺序返回字节数组的。
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BitConverter.GetBytes 方法以什么顺序返回字节数组
标签：
原文地址：http://blog.csdn.net/u013141940/article/details/47163923
