MC6800/6809: fix BGT/LBGT branch condition (uses Carry instead of Zero)#9276
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djmips wants to merge 1 commit into
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MC6800/6809: fix BGT/LBGT branch condition (uses Carry instead of Zero)#9276djmips wants to merge 1 commit into
djmips wants to merge 1 commit into
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ryanmkurtz
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Feature: Processor/MC6800
Status: Triage
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BGT(opcode0x2E) andLBGT(PAGE2,op=0x2E) inGhidra/Processors/MC6800/data/languages/6x09.sinctest the Carry flag:Per the MC6809 programming manual, signed
BGTbranches onZ==0 AND (N == V); carry is not involved. This is corroborated internally byBLE(0x2F), the logical complement ofBGT, which is correctly implemented as(N^V) | Z— so as written,BGTandBLEare not complements.Example:
LDX #$0060; CMPX #$005F; BGT t(96 > 95; N=V=Z=0, C=0) fails to branch.Fix: in
BGTandLBGT, replace& $(C)with& ($(Z) == 0).BGE/BLT/BLEand the long-branch forms are already correct.Verified with
gradle :MC6800:sleighCompile— all three MC6800 languages compile with no errors.