Question

I have to do this program where i have to use a register which can be anything between 1 to 20 bits long. i could only think of using a character array for this purpose. I want to left shift(by 1), reset the nth bit and set or reset the 0th bit depending on a condition. Since i do not know the number of bits until at run time, i am using using malloc to allocate the size of the character array. Please tell me if this is correct

// history bits can change from 1 to 20
int historyRegisterSize=(historybits+7)/8;

// allocating memory dynamically
historyRegister=malloc(historyRegisterSize * sizeof(unsigned char));

// Shifting left one bit
    unsigned char *byte;
    int size=historyRegisterSize;
    for( byte =historyRegister; size--; ++byte )
    {
        unsigned char bit = 0;
        if (size>=0)
        {
            bit = byte[1] & (1 << (8 - 1)) ? 1 : 0;
        }
        *byte <<= 1;
        *byte |= bit;
    }

    // Resetting the nth bit 
    historyRegister[0]=historyRegister[0] & 0x7;

     // or should i use this one for resetting?
     //historyRegister[historyRegisterSize-1] &= ~(1 <<(historybits-1));

    // Setting the 0th bit based on a condition
    if(condition)
    {
        historyRegister[historyRegisterSize-1]=historyRegister[historyRegisterSize-1] | 1;
        // or should i use this statement below?
        //historyRegister[0] |= 1 <<0;
    }
    else
    {
    historyRegister[historyRegisterSize-1]=historyRegister[historyRegisterSize-1] & 0xfe;
      // or should i use this statement below?
      //historyRegister[0] &= ~(1 <<0);
    }

在这样做之后,我只想把64个字塔与我的特性阵列(历史重新编号)毫不相干,并作成组合。为此,我使用本声明。

// result and var2 and unsigned long variables 
// and size is another unsigned integer.
result=(var1 ^ *(unsigned long int *)historyRegister) % size;

一切似乎都是正确的? 我的问题是,当我改变特性阵列的比值时,产出价值在范围上似乎保持不变。这一数字从1比8比8,8比16,16比20。是否与万国主义相差错?

而且,除了使用特性阵列之外,它还有更好的选择?

Answer 1

If you only need to store 20 bits it would be easier to use an unsigned int or long. Shifting could then be done by

val <<= 1;

你们可以躲避最左边的东西。

val &= ((1u <<n) -1);

友情链接