Well one way you could do it is with a for loop, but that would only really be efficient if the bit masks are consecutive. I only know Java, so I might get the C++ syntax wrong, but here is what it might look like:
Code:
int keys = keysHeld();
byte packedKeys = 0;
for (int i = 0; i < 8; i++) {
if (keys & (1 << i)) packedKeys |= 1 << i;
}
That would pack the values of the keys, but only if the bit masks were all in a line. You could also start the i variable at the first mask if it isn't zero. I have the same question as mikets though. Why do you even need to do this if keysHeld() already returns the key values? It seems redundant to me.