Recomended formating for temporarily inverting data at pointer and then passing pointer to temporari-CodePudding

Long story short, I have a pointer to a value that is stored inverted, so when we are calculating a hash to verify data integrety, we need to invert the data that is used in the hash. The hash function, however, takes a pointer as input. So what we need to do is take our pointer, dereference it to get to the data, temporarily invert the data, and the pass a reference to the inverted data.

I've written up some pseudocode for how I had originally done it.

uint32_t hash = 0;
MemoryBlock pMemoryBlock = pAllocator->GetFirstMemoryBlock();
while(nullptr != pMemoryBlock)
{
    uint32_t size = pMemoryBlock->getWordsUsed();
    const uint32_t* pStartAddress = pMemoryBlock->GetStartAddress();
    for (uint32_t i = 0; i < size; i  )
    {
        if (isDiagnostics)
        {
            uint32_t inverted_data = ~(pStartAddress[i]);
            hash = Algorithim::Calculate(&inverted_data, hash);
        }
        else
        {
            hash = Algorithim::Calculate(&pStartAddress[i], hash);
        }
    }
    pMemoryBlock->GetNextMemoryBlock();
}
return hash;

But a colleague on my code review wants me to avoid the temp variable and change it to.

uint32_t hash = 0;
MemoryBlock pMemoryBlock = pAllocator->GetFirstMemoryBlock();
while(nullptr != pMemoryBlock)
{
    uint32_t size = pMemoryBlock->getWordsUsed();
    const uint32_t* pStartAddress = pMemoryBlock->GetStartAddress();
    for (uint32_t i = 0; i < size; i  )
    {
        if (isDiagnostics)
        {
            hash = Algorithim::Calculate(&~pStartAddress[i], hash);
        }
        else
        {
            hash = Algorithim::Calculate(&pStartAddress[i], hash);
        }
    }
    pMemoryBlock->GetNextMemoryBlock();
}
return hash;

I was wondering if there was any real reason to avoid using the temp variable. If it even works to dereference a pointer, do an operator on the data, and then pass a reference to it without assigning the value to anything (cause i'm fairly certain it doesn't). And if there are any better ways to do this than the first example.

CodePudding user response：

You need the temp variable. This expression:

hash = Algorithim::Calculate(&~pStartAddress[i], hash);

Is invalid because the result of the ~ operator is not an lvalue, and the & operator requires an lvalue.

On a side note, you can reduce repetition in your code by using the temp value in both cases:

    uint32_t data = isDiagnostics ? ~pStartAddress[i] : pStartAddress[i];
    hash = Algorithim::Calculate(&data, hash);