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

You should measure rather than guess at any potential improvement but my first thought is that it may be faster to do a union as follows:

typedef union {
    DWORD d;
    struct {
        BYTE b0;
        BYTE b1;
        BYTE b2;
        BYTE b3;
    } b;
} DWB;

std::vector compBytes;
DWB invLen;
invLen.d = (DWORD) invalidClsids.length();
compBytes.push_back(invalidLength.b.b3);
compBytes.push_back(invalidLength.b.b2);
compBytes.push_back(invalidLength.b.b1);
compBytes.push_back(invalidLength.b.b0);

That may be the right order for the pushbacks but check just in case - it depends on the endian-ness of the CPU.