I seem to recall that Intel and AMD CPUs will behave in strange and unusual ways, particularly when it comes to things like bitshift op flags, if you shift by out of range values, or by 0 or 1. So I guess undefined behaviors in C are somewhat consistent with CPUs. But as other people mentioned Intel is much more forgiving than X3J11. If you ever wanted to find all the dirty corner cases that exist between ANSI and hardware, I swear, try writing C functions that emulate the hardware, and then fuzz the two lockstep style. It's harder than you'd think. [don't click here if you intend to try that: https://github.com/jart/cosmopolitan/blob/master/tool/build/...]