Agreed. I think it was only a problem because of ubsan. I guess ubsan added checks to the generated code that looked at the value being shifted left 24 and saw that overflow occurred and therefore raised its undefined behaviour signal.

The code would never fail on a two's compliment machine. What ubsan is saying is that the rules of C don't guarantee this code to work - it only works because the overflow writes into the sign bit, which is where the next thing expected it to be anyway.

If the above is true, I don't think their "fix" helps: https://github.com/glfw/glfw/pull/1986/files. I would have thought that the important part is to change the longs to unsigned longs. Edit: Ah, right, that's what the discussion says: https://github.com/glfw/glfw/pull/1986