Fastest Method to Split a 32 Bit number into Bytes in C++

Question

I am writing a piece of code designed to do some data compression on CLSID structures. I\'m storing them as a compressed stream of 128 bit integers. However, the code in questio

Answer 1

Just use a union:

assert(sizeof (DWORD) == sizeof (BYTE[4]));   // Sanity check

union either {
    DWORD dw;
    struct {
         BYTE b[4];
    } bytes;
};

either invalidLength;
invalidLength.dw = (DWORD) invalidClsids.length();
compressedBytes.push_back(either.bytes.b[0]);
compressedBytes.push_back(either.bytes.b[1]);
compressedBytes.push_back(either.bytes.b[2]);
compressedBytes.push_back(either.bytes.b[3]);

NOTE: Unlike the bit-shifting approach in the original question, this code produces endian-dependent output. This matters only if output from a program running on one computer will be read on a computer with different endianness -- but as there seems to be no measurable speed increase from using this method, you might as well use the more portable bit-shifting approach, just in case.