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spjewkes / jrnz

A work-in-progress ZX Spectrum emulator
MIT License
1 stars 0 forks source link

Need to investigate the half carry flag #33

Closed spjewkes closed 6 months ago

spjewkes commented 6 months ago

I'm not convinced this works correctly at all and it needs some investigation

For the NEG instruction we had the value 0x28 being negated. The result was 0xD8 and the expectation is that both the carry and half carry flags should be set.

The half carry flag is not set.

spjewkes commented 6 months ago

I believe both this and the carry flag should now be working. As I originally wrote in the code, we should just behave in the same way as the 8-bit version but that was terminally broken. Now that is fixed we seem to be getting all tests passing relating to maths with z80doc. So for now I'm closing this ticket.