C / C ++ code对待一个字符数组为比特流 [英] C/C++ Code to treat a character array as a bitstream

问题描述

我有二进制数据的一个char []数组一大坨，我需要间preT外带6位值的数组。

我的可能的坐下来写一些code这样做，但我想有必须有一个良好的现存类或函数有人已经写的。

我需要的是这样的：

  INT get_bits（字符*数据，符号bitOffset，无符号NUMBITS）;
 

所以我可以通过调用获取数据第七届6位字符：

  const的无符号BITSIZE = 6;
焦炭CH =的static_cast＆LT;＆烧焦GT;（get_bits（数据，7 * BITSIZE，BITSIZE））;
 

解决方案

这可能不适用于尺寸大于8的工作，这取决于endian系统。这基本上就是马可·贴，虽然我不完全知道为什么他会在一个时间聚集一位。

  INT get_bits（字符*数据，无符号整型bitOffset，无符号整型NUMBITS）{
    NUMBITS = POW（2 NUMBITS） -  1; //这只会工作到32位，当然
    数据+ = bitOffset / 8;
    bitOffset％= 8;
    返回（*（为（int *）数据）GT;＆GT; bitOffset）及NUMBITS; //小尾数
    //回报（翻转（数据[0]）GT;＆GT; bitOffset）及NUMBITS; //大端
}//从大翻转很少或反之亦然
INT翻转（INT X）{
    焦炭温度，* T =（字符*）及X;
    TEMP = T [0];
    T [0] = T [3];
    T [3] =温度;
    TEMP = T [1];
    T [1] = T [2];
    T [2] =温度;
    返回X;
}
 

I have a big lump of binary data in a char[] array which I need to interpret as an array of packed 6-bit values.

I could sit down and write some code to do this but I'm thinking there has to be a good extant class or function somebody has written already.

What I need is something like:

int get_bits(char* data, unsigned bitOffset, unsigned numBits);

so I could get the 7th 6-bit character in the data by calling:

const unsigned BITSIZE = 6;
char ch = static_cast<char>(get_bits(data, 7 * BITSIZE, BITSIZE));

解决方案

This may not work for sizes greater than 8, depending on endian system. It's basically what Marco posted, though I'm not entirely sure why he'd gather one bit at a time.

int get_bits(char* data, unsigned int bitOffset, unsigned int numBits) {
    numBits = pow(2,numBits) - 1; //this will only work up to 32 bits, of course
    data += bitOffset/8;
    bitOffset %= 8;
    return (*((int*)data) >> bitOffset) & numBits;  //little endian
    //return (flip(data[0]) >> bitOffset) & numBits; //big endian
}

//flips from big to little or vice versa
int flip(int x) {
    char temp, *t = (char*)&x;
    temp = t[0];
    t[0] = t[3];
    t[3] = temp;
    temp = t[1];
    t[1] = t[2];
    t[2] = temp;
    return x;
}

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