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Slightly clean up shift code.

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This commit is contained in:
Thomas Harte 2024-04-01 21:24:49 -04:00
parent 0866caf934
commit 7de92a9457
1 changed files with 7 additions and 21 deletions
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28
InstructionSets/ARM/Executor.hpp
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@ -58,9 +58,11 @@ struct Executor {
operand2 = registers_[fields.operand2()];
}
uint32_t shift_amount;
// TODO: in C++20, a quick `if constexpr (requires` can eliminate the `allow_register` parameter.
if constexpr (allow_register) {
if(fields.shift_count_is_register()) {
uint32_t shift_amount;
// "When R15 appears in either of the Rn or Rs positions it will give the value
// of the PC alone, with the PSR bits replaced by zeroes. ...
//
@ -77,17 +79,14 @@ struct Executor {
// A register shift amount of 0 has a different meaning than an in-instruction
// shift amount of 0.
if(!shift_amount) {
return operand2;
if(shift_amount) {
shift<set_carry>(fields.shift_type(), operand2, shift_amount, rotate_carry);
}
} else {
shift_amount = fields.shift_amount();
return operand2;
}
} else {
shift_amount = fields.shift_amount();
}
shift<set_carry>(fields.shift_type(), operand2, shift_amount, rotate_carry);
shift<set_carry>(fields.shift_type(), operand2, fields.shift_amount(), rotate_carry);
return operand2;
}
@ -306,15 +305,6 @@ struct Executor {
// TODO: resolve uncertainty.
constexpr bool should_write_back = !flags.pre_index() || flags.write_back_address();
// STR: update prior to write.
// if constexpr (should_write_back && flags.operation() == SingleDataTransferFlags::Operation::STR) {
// if(transfer.base() == 15) {
// registers_.set_pc(offsetted_address);
// } else {
// registers_[transfer.base()] = offsetted_address;
// }
// }
// "... post-indexed data transfers always write back the modified base. The only use of the [write-back address]
// bit in a post-indexed data transfer is in non-user mode code, where setting the W bit forces the /TRANS pin
// to go LOW for the transfer"
@ -375,10 +365,6 @@ struct Executor {
}
}
// LDR: write back after load, only if original wasn't overwritten.
// if constexpr (should_write_back && flags.operation() == SingleDataTransferFlags::Operation::LDR) {
// if(transfer.base() != transfer.destination()) {
if constexpr (should_write_back) {
// Empirically: I think writeback occurs before the access, so shouldn't overwrite on a load.
if(flags.operation() == SingleDataTransferFlags::Operation::STR || transfer.base() != transfer.destination()) {