Divide-by-zero and division overflow handling

[randomsleep]

According to the RISC-V spec, divide-by-zero and division overflow won't raise exception. Instead, it will return specific values.

In Jolt DIV, DIVU, REM, and REMU instruction this is not handled. There is AssertValidDiv0Instruction but it seems it is not used.

[moodlezoup]

It should be handled, for the division and remainder instructions Jolt uses "virtual sequences" (see Section 6.2 of the Jolt paper and this section of the Jolt book). This is where e.g. the AssertValidDiv0Instruction arises (see div.rs). Feel free to reopen this issue if I'm missing something

[randomsleep]

@moodlezoup Oh thanks! The code already handled that. The Jolt paper didn't mention these AssertValidDiv0Instruction instruction in DIV.

The sequence_output in divu and remu should be updated according to that?

jolt/jolt-core/src/jolt/instruction/divu.rs

Lines 230 to 232 in 0220448

	fn sequence_output(x: u64, y: u64) -> u64 {
	x / y
	}

[moodlezoup]

Ah yes, nice catch. That method's only used in tests so not super urgent but will make a note to fix!

#499