Unnecessary use of std::vector::push_back() in "cp2130.cpp", line 958

[samuelfmlourenco]

Inside the file "cp2130.cpp", in line 958, there is an instance where std::vector::push_back() is being used in order to add elements to retdata from writeReadInputBuffer. An excerpt of spiWriteRead(), the function which contains said line, follows:

// Writes to the SPI bus while reading back, returning a vector of the same size as the one given
// This is the prefered method of writing and reading, if both endpoint addresses are known
std::vector<uint8_t> CP2130::spiWriteRead(const std::vector<uint8_t> &data, uint8_t endpointInAddr, uint8_t endpointOutAddr, int &errcnt, std::string &errstr)
{
    size_t bytesToWriteRead = data.size();
    size_t bytesLeft = bytesToWriteRead;
    std::vector<uint8_t> retdata;
...
        int bytesRead = 0;  // Important!
        bulkTransfer(endpointInAddr, writeReadInputBuffer, payload, &bytesRead, errcnt, errstr);
        for (int i = 0; i < bytesRead; ++i) {
            retdata.push_back(writeReadInputBuffer[i]);
        }
...
    return retdata;
}

However, std::vector::push_back() is a slower operation than just assigning a value to an element that already exists. Once the number of bytes read is known, retdata could be resized and then the values assigned to it:

// Writes to the SPI bus while reading back, returning a vector of the same size as the one given
// This is the prefered method of writing and reading, if both endpoint addresses are known
std::vector<uint8_t> CP2130::spiWriteRead(const std::vector<uint8_t> &data, uint8_t endpointInAddr, uint8_t endpointOutAddr, int &errcnt, std::string &errstr)
{
    size_t bytesToWriteRead = data.size();
    size_t bytesLeft = bytesToWriteRead;
    std::vector<uint8_t> retdata;
...
        int bytesRead = 0;  // Important!
        bulkTransfer(endpointInAddr, writeReadInputBuffer, payload, &bytesRead, errcnt, errstr);
        retdata.resize(static_cast<size_t>(bytesRead));
        for (int i = 0; i < bytesRead; ++i) {
            retdata[i] = writeReadInputBuffer[i];
        }
...
    return retdata;
}

[samuelfmlourenco]

Implemented in version 1.2.2.