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0 pointsrseacord6y ago0 comments

Some example of hardware variation (since you mentioned shifting and overflow):

- signed integer overflow or division by zero occurs, a division instruction traps on x86, while it silently produces an undefined result on PowerPC - left-shifting a 32-bit one by 32 bits yields 0 on ARM and PowerPC, but 1 on x86; - left-shifting a 32-bit one by 64 bits yields 0 on ARM, but 1 on x86 and PowerPC

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BeeOnRope6y ago

On x86 it's actually mixed: scalar shifts behave as you describe, but vectorised logical shifts flush to zero when the shift amount is greater than the element size!

So x86 actually has both behaviors in one box (three behaviors if you could the 32-bit and 64-bit scalar things you mentioned separately).

This is an example of where UB for simple operations actually helps even on a single hardware platform: it allows efficient vectorization.

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