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The PSX has a few undefined cases when it comes to division. It's important to remeber than undefined isn't the same as inconsistent or unstable, and as a result, there are games out the which relies on this undefined behavior.

Signed division by zero

The result of a division by zero is consistent with the result of a smiple radix-2 (“one bit at a time”) implementation. That is, if the dividend is negative, the result is 1 (0x00000001), and if the dividend is positive or zero, the result is -1 (0xffffffff). In both cases the remainder equals the dividend.

Unsigned division by zero

Signed division of most negative by minus one