将位插入字节

发布于 2024-09-01 11:36:54 字数 671 浏览 10 评论 0原文

我正在看一个从字节读取位的示例，其实现看起来简单且易于理解。我想知道是否有人有类似的示例来说明如何将位插入字节或字节数组，这更容易理解并且也像下面的示例一样实现。

    static int GetBits3(byte b, int offset, int count)
    {
           return (b >> offset) & ((1 << count) - 1);
    }

这就是我想要做的。这是我当前的实现，我只是对位掩码/移位等有点困惑，所以我试图找出是否有更简单的方法来完成我正在做的事情

BYTE Msg[2];
Msg_Id = 3;
Msg_Event = 1;
Msg_Ready = 2;

Msg[0] = ( ( Msg_Event << 4 ) & 0xF0 ) | ( Msg_Id & 0x0F ) ;
Msg[1] = Msg_Ready  & 0x0F;     //MsgReady & Unused

原文

I was looking at an example of reading bits from a byte and the implementation looked simple and easy to understand. I was wondering if anyone has a similar example of how to insert bits into a byte or byte array, that is easier to understand and also implement like the example below.

Here is the example I found of reading bits from a byte:

    static int GetBits3(byte b, int offset, int count)
    {
           return (b >> offset) & ((1 << count) - 1);
    }

Here is what I'm trying to do. This is my current implementation, I'm just a little confused with the bit-masking/shifting, etc., so I'm trying to find out if there is an easier way to do what I'm doing

BYTE Msg[2];
Msg_Id = 3;
Msg_Event = 1;
Msg_Ready = 2;

Msg[0] = ( ( Msg_Event << 4 ) & 0xF0 ) | ( Msg_Id & 0x0F ) ;
Msg[1] = Msg_Ready  & 0x0F;     //MsgReady & Unused

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苄①跕圉湢 2024-09-08 11:36:54

如果您使用连续的整数常量值（如上例所示），则在将这些常量放入字节中时，应使用这些常量移动位。否则它们会重叠：在您的示例中， Msg_Id 等于 Msg_Event &消息_就绪。这些可以像这样使用

Msg[0] = ( 1 << Msg_Event ) | ( 1 << Msg_Id); // sets the 2nd and 4th bits

（请注意，字节内的位从 0 开始索引。）另一种方法是使用 2 的幂作为常量值：

Msg_Id = 4;    // equals 1 << 2
Msg_Event = 1; // equals 1 << 0
Msg_Ready = 2; // equals 1 << 1

请注意，在上面的代码中，使用 0x0F 或 < code>0xF0 并不是真正需要的：(Msg_Id & 0x0F) == Msg_Id 和 ((Msg_Event << 4) & 0xF0) == (Msg_Event < ;<4)。

If you are using consecutive integer constant values like in the example above, you should shift the bits with these constants when putting them inside a byte. Otherwise they overlap: in your example, Msg_Id equals Msg_Event & Msg_Ready. These can be used like

Msg[0] = ( 1 << Msg_Event ) | ( 1 << Msg_Id); // sets the 2nd and 4th bits

(Note that bits within a byte are indexed from 0.) The other approach would be using powers of 2 as constant values:

Msg_Id = 4;    // equals 1 << 2
Msg_Event = 1; // equals 1 << 0
Msg_Ready = 2; // equals 1 << 1

Note that in your code above, masking with 0x0F or 0xF0 is not really needed: (Msg_Id & 0x0F) == Msg_Id and ((Msg_Event << 4) & 0xF0) == (Msg_Event << 4).

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夜司空 2024-09-08 11:36:54

您可以使用位字段。例如：

struct Msg
{
   unsigned MsgEvent  : 1; // 1 bit
   unsigned MsgReady  : 1; // 1 bit
};

然后您可以使用联合来操作位域或字节，如下所示：

struct MsgBitField {
   unsigned MsgEvent : 1; // 1 bit
   unsigned MsgReady : 1; // 1 bit
};

union ByteAsBitField {
   unsigned char Byte;
   MsgBitField Message;
};

int main() {
   ByteAsBitField MyByte;
   MyByte.Byte = 0;
   MyByte.Message.MsgEvent = true;
}

You could use a bit field. For instance :

struct Msg
{
   unsigned MsgEvent  : 1; // 1 bit
   unsigned MsgReady  : 1; // 1 bit
};

You could then use a union to manipulate either the bitfield or the byte, something like this :

struct MsgBitField {
   unsigned MsgEvent : 1; // 1 bit
   unsigned MsgReady : 1; // 1 bit
};

union ByteAsBitField {
   unsigned char Byte;
   MsgBitField Message;
};

int main() {
   ByteAsBitField MyByte;
   MyByte.Byte = 0;
   MyByte.Message.MsgEvent = true;
}

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