在INT替换字节 [英] Replace byte in a int
问题描述
一个INT由4个字节。我怎么能取代那些4个字节一个新的字节之一。换句话说,我要寻找一个方法:
INT ReplaceByte(INT指数,int值,字节replaceByte)
{
//执行
}
例如,如果我有值 FFFFFFFF
(-1),我会想更换个字节 0
与 0A
(10),那么我会调用该方法为:
ReplaceByte(0,-1,10)
和我会喜欢这个方法返回我 FFFFFF0A
我必须转换INT为一个字节数组,然后替换字节我想然后再转换回一个int?我要寻找这样的一个有效途径。我们正在建立类似的程序调试器连接到目标(板),我们很频繁地更新这些值。
编辑(结果)
感谢您的回答我比较方法:
下面是结果:
注意我的执行是最慢的!
下面是code:
静态无效的主要(字串[] args)
{
字节[] = randomBytes新的字节[1024 * 1024 * 512]; 随机R =新的随机();
r.NextBytes(randomBytes); Int64的总和;
VAR现在= DateTime.Now; Console.WriteLine(测试1);
总和= 0;
现在= DateTime.Now;
的foreach(在randomBytes VAR BT)
{
总和+ = ReplaceByte1(1,-1,BT);
} Console.WriteLine((DateTime.Now测试1 {0}秒\\ t哈希= {1} \\ n完成 - 现在).TotalSeconds,总和); Console.WriteLine(试验2);
总和= 0;
现在= DateTime.Now;
的foreach(在randomBytes VAR BT)
{
总和+ = ReplaceByte2(1,-1,BT);
} Console.WriteLine((DateTime.Now测试2 {0}秒\\ t哈希= {1} \\ n完成 - 现在).TotalSeconds,总和);
Console.WriteLine(测试3);
总和= 0;
现在= DateTime.Now;
的foreach(在randomBytes VAR BT)
{
总和+ = ReplaceByte3(1,-1,BT);
} Console.WriteLine((DateTime.Now测试3 {0}秒\\ t哈希= {1} \\ n完成 - 现在).TotalSeconds,总和); Console.Read();
} //测试1
静态INT ReplaceByte1(INT指数,int值,字节replaceByte)
{
收益率(值和放大器;〜(0xFF的<<(指数* 8)))| (replaceByte&所述;≤(指数* 8));
} //测试2
静态INT ReplaceByte2(INT指数,int值,字节replaceByte)
{
//你应该有多少位转移replaceByte把它到位
变种shiftBits = 8 *指数; //位与此同值来清除应该成为replaceByte位
VAR面膜=〜(0xFF的<< shiftBits); //清除这些位,然后将它们设置为任何replaceByte是
返回值及放大器;面膜| (replaceByte<< shiftBits);
} //测试3
静态INT ReplaceByte3(INT指数,int值,字节replaceByte)
{
VAR字节= BitConverter.GetBytes(值);
字节[指数] = replaceByte; 返回BitConverter.ToInt32(字节,0);
}
没有,没有字节数组。这其实很简单。
没有测试:
INT ReplaceByte(INT指数,int值,字节replaceByte)
{
收益率(值和放大器;〜(0xFF的<<(指数* 8)))| (replaceByte&所述;≤(指数* 8));
}
首先,它清除指定索引处的空间在哪里,然后它把新的价值空间。
A int is composed of 4 bytes. How could I replace one of those 4 bytes with a new byte. In other words I am looking for a method:
int ReplaceByte(int index, int value, byte replaceByte)
{
// implementation
}
for example if I have the value FFFFFFFF
(-1) and I will like to replace the byte 0
with 0A
(10) then I will call the method as:
ReplaceByte(0,-1,10)
and I will like that method to return me FFFFFF0A
Do I have to convert the int to a byte array then replace the byte I want then convert back to an int? I am looking for an efficient way of doing this. We are creating a debugger like program that connects to a target (board) and we update these values very frequently.
Edit (results)
Thanks to your answers I compared the methods:
here are the results:
Note my implementation was the slowest!
Here is the code:
static void Main ( string[ ] args )
{
byte[ ] randomBytes = new byte[ 1024 * 1024 * 512 ];
Random r = new Random( );
r.NextBytes( randomBytes );
Int64 sum;
var now = DateTime.Now;
Console.WriteLine( "Test 1" );
sum = 0;
now = DateTime.Now;
foreach ( var bt in randomBytes )
{
sum += ReplaceByte1( 1 , -1 , bt );
}
Console.WriteLine( "Test 1 finished in {0} seconds \t hash = {1} \n" , ( DateTime.Now - now ).TotalSeconds, sum );
Console.WriteLine( "Test 2" );
sum = 0;
now = DateTime.Now;
foreach ( var bt in randomBytes )
{
sum += ReplaceByte2( 1 , -1 , bt );
}
Console.WriteLine( "Test 2 finished in {0} seconds \t hash = {1} \n" , ( DateTime.Now - now ).TotalSeconds, sum );
Console.WriteLine( "Test 3" );
sum = 0;
now = DateTime.Now;
foreach ( var bt in randomBytes )
{
sum += ReplaceByte3( 1 , -1 , bt );
}
Console.WriteLine( "Test 3 finished in {0} seconds \t hash = {1} \n" , ( DateTime.Now - now ).TotalSeconds , sum );
Console.Read( );
}
// test 1
static int ReplaceByte1 ( int index , int value , byte replaceByte )
{
return ( value & ~( 0xFF << ( index * 8 ) ) ) | ( replaceByte << ( index * 8 ) );
}
// test 2
static int ReplaceByte2 ( int index , int value , byte replaceByte )
{
// how many bits you should shift replaceByte to bring it "in position"
var shiftBits = 8 * index;
// bitwise AND this with value to clear the bits that should become replaceByte
var mask = ~( 0xff << shiftBits );
// clear those bits and then set them to whatever replaceByte is
return value & mask | ( replaceByte << shiftBits );
}
// test 3
static int ReplaceByte3 ( int index , int value , byte replaceByte )
{
var bytes = BitConverter.GetBytes( value );
bytes[ index ] = replaceByte;
return BitConverter.ToInt32( bytes , 0 );
}
No, no bytes arrays. This actually very simple.
Not tested:
int ReplaceByte(int index, int value, byte replaceByte)
{
return (value & ~(0xFF << (index * 8))) | (replaceByte << (index * 8));
}
First it clears the space where at the specified index, and then it puts the new value in that space.
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