For MPC601 CPUs, all values of rA return 64 though the manual says undefined values of rA produce undefined results.
For non-MPC601 CPUs, if this instruction is included (such as for risu DPPC) then return results that are obtained from a G4 running Mac OS 9.2.2.
Making a negative value positive requires unary negate operator rather than binary and operator since negative numbers are stored using twos compliment.
If ov is set then clear overflow when overflow doesn't happen.
- Rename DEC to DEC_S and add DEC_U.
- MQ, RTCL_U, RTCU_U, and DEC_U should cause an illegal instruction program exception for non-MPC601 CPUs. The exception handler of classic Mac OS uses this to emulate the instruction.
- For mtspr, the SPRs RTCL_U, RTCU_U, and DEC_U are treated as no-op on MPC601.
- For debugging, use the supervisor instead of the user SPR number as the index for storing the values for RTC, TB, and DEC.
- For debugging, RTC, TB, and DEC should be updated after each access. Previously, mfspr and mtspr would only update the half of RTC and TB that was being accessed instead of both halves.
Accessing an SPR with bit 4 set (> 15) requires supervisor privilege and should cause a supervisor-level instruction exception (privileged instruction type program exception).
The first option is a flag that enables MPC601 (POWER) instructions for CPUs that are not MPC601.
This can be useful for the following reasons:
1) To produce results similar to classic Mac OS which emulates MPC601 instructions on CPUs that don't implement MPC601 instructions. This option is used to compare the risu traces produced in Mac OS 9 on a G3 or G4 with DPPC.
2) May increase performance in apps that use POWER instructions on emulated machines with CPUs that are not MPC601. It is not known if any such apps exist but there could be since Apple included MPC601 emulation in classic Mac OS.
I don't know if the compiler is smart enough to figure out that ((guest_va & 0xFFF) + sizeof(T)) > 0x1000) is always false when sizeof(T) == 1 so we'll add a check for sizeof(T) > 1.
Instructions that are 8 characters or longer (such as mtdbat3l) did not have a space between opcode and operand. Now there is always a space. The width of the opcode column is unchanged except for those opcodes that have 8 or more characters.
Use "logical" since the functions deal with multiple bits instead of a single boolean value and because the 601 manual calls them Logical Instructions.
Use "ppc" for the enums because logical_and is defined elsewhere and because the original DPPC code used these names for those functions.
