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Fix overflow flags, avoid bigger-word usage.

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This commit is contained in:
Thomas Harte 2022-10-16 21:52:00 -04:00
parent 17c1e51231
commit d5ceb934d2
1 changed files with 31 additions and 31 deletions
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52
InstructionSets/M68k/Implementation/PerformImplementation.hpp
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@ -251,11 +251,6 @@ template <typename IntT> void set_neg_zero(IntT result, Status &status) {
status.negative_flag = result & top_bit<IntT>();
}
template <typename IntT> void set_neg_zero_overflow(IntT result, IntT destination, Status &status) {
set_neg_zero<IntT>(result, status);
status.overflow_flag = Status::FlagT((destination ^ result) & top_bit<IntT>());
}
/// Perform a rotate without extend, i.e. any of RO[L/R].[b/w/l].
template <Operation operation, typename IntT, typename FlowController> void rotate(uint32_t source, IntT &destination, Status &status, FlowController &flow_controller) {
static_assert(
@ -265,31 +260,30 @@ template <Operation operation, typename IntT, typename FlowController> void rota
const auto size = bit_size<IntT>();
const auto shift = shift_count<IntT>(uint8_t(source), flow_controller) & (size - 1);
IntT result;
if(!shift) {
result = destination;
status.carry_flag = 0;
} else {
switch(operation) {
case Operation::ROLb: case Operation::ROLw: case Operation::ROLl:
result = IntT(
destination = IntT(
(destination << shift) |
(destination >> (size - shift))
);
status.carry_flag = Status::FlagT(destination & 1);
break;
case Operation::RORb: case Operation::RORw: case Operation::RORl:
result = IntT(
destination = IntT(
(destination >> shift) |
(destination << (size - shift))
);
status.carry_flag = Status::FlagT(destination & top_bit<IntT>());
break;
}
status.carry_flag = Status::FlagT(result & 1);
}
set_neg_zero_overflow(result, destination, status);
destination = IntT(result);
set_neg_zero(destination, status);
status.overflow_flag = 0;
}
/// Perform a rotate-through-extend, i.e. any of ROX[L/R].[b/w/l].
@ -300,28 +294,34 @@ template <Operation operation, typename IntT, typename FlowController> void rox(
);
const auto size = bit_size<IntT>();
const auto shift = shift_count<IntT>(uint8_t(source), flow_controller) % (size + 1);
uint64_t compound =
uint64_t(destination) |
(status.extend_flag ? (1ull << size) : 0);
auto shift = shift_count<IntT>(uint8_t(source), flow_controller) % (size + 1);
if(!shift) {
// When shift is zero, extend is unaffected but is copied to carry.
status.carry_flag = status.extend_flag;
} else {
switch(operation) {
case Operation::ROXLb: case Operation::ROXLw: case Operation::ROXLl:
compound =
(compound << shift) |
(compound >> (size + 1 - shift));
status.carry_flag = status.extend_flag = Status::FlagT((destination >> (size - shift)) & 1);
destination = IntT(
(destination << shift) |
(IntT(status.extend_flag ? 1 : 0) << (shift - 1)) |
(destination >> (size + 1 - shift))
);
break;
case Operation::ROXRb: case Operation::ROXRw: case Operation::ROXRl:
compound =
(compound >> shift) |
(compound << (size + 1 - shift));
status.carry_flag = status.extend_flag = Status::FlagT(destination & (1 << (shift - 1)));
destination = IntT(
(destination >> shift) |
((status.extend_flag ? top_bit<IntT>() : 0) >> (shift - 1)) |
(destination << (size + 1 - shift))
);
break;
}
}
status.carry_flag = status.extend_flag = Status::FlagT((compound >> size) & 1);
set_neg_zero_overflow(IntT(compound), destination, status);
destination = IntT(compound);
set_neg_zero(destination, status);
status.overflow_flag = 0;
}
}