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Add various insurances against undefined behaviour.

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This commit is contained in:
Thomas Harte 2022-10-18 11:30:40 -04:00
parent a364499d17
commit a1ae7c28b2
1 changed files with 80 additions and 41 deletions
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83
InstructionSets/M68k/Implementation/PerformImplementation.hpp
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@ -325,7 +325,7 @@ template <Operation operation, typename IntT, typename FlowController> void shif
operation == Operation::LSRb || operation == Operation::LSRw || operation == Operation::LSRl
);
const auto size = bit_size<IntT>();
constexpr auto size = bit_size<IntT>();
const auto shift = shift_count<IntT>(uint8_t(source), flow_controller);
if(!shift) {
@ -352,30 +352,46 @@ template <Operation operation, typename IntT, typename FlowController> void shif
switch(type) {
case Type::ASL:
case Type::LSL:
status.overflow_flag =
type == Type::LSL ?
0 : (destination ^ (destination << shift)) & top_bit<IntT>();
if(shift < size) {
status.carry_flag = status.extend_flag = (destination >> (size - shift)) & 1;
} else {
if(shift > size) {
status.carry_flag = status.extend_flag = 0;
} else {
status.carry_flag = status.extend_flag = (destination << (shift - 1)) & top_bit<IntT>();
}
if(type == Type::LSL) {
status.overflow_flag = 0;
} else {
if(shift >= size) {
status.overflow_flag = destination & top_bit<IntT>();
} else {
status.overflow_flag = (destination ^ (destination << shift)) & top_bit<IntT>();
}
}
if(shift >= size) {
destination = 0;
} else {
destination <<= shift;
}
break;
case Type::ASR:
case Type::LSR: {
if(shift > size) {
status.carry_flag = status.extend_flag = 0;
} else {
status.carry_flag = status.extend_flag = (destination >> (shift - 1)) & 1;
}
status.overflow_flag = 0;
const IntT sign_word =
type == Type::LSR ?
0 : (destination & top_bit<IntT>() ? IntT(~0) : 0);
status.overflow_flag = 0;
status.carry_flag = status.extend_flag = (destination >> (shift - 1)) & 1;
if(shift < size) {
destination = IntT((destination >> shift) | (sign_word << (size - shift)));
} else {
if(shift >= size) {
destination = sign_word;
} else {
destination = IntT((destination >> shift) | (sign_word << (size - shift)));
}
} break;
}
@ -391,7 +407,7 @@ template <Operation operation, typename IntT, typename FlowController> void rota
operation == Operation::RORb || operation == Operation::RORw || operation == Operation::RORl
);
const auto size = bit_size<IntT>();
constexpr auto size = bit_size<IntT>();
auto shift = shift_count<IntT>(uint8_t(source), flow_controller);
if(!shift) {
@ -401,17 +417,21 @@ template <Operation operation, typename IntT, typename FlowController> void rota
switch(operation) {
case Operation::ROLb: case Operation::ROLw: case Operation::ROLl:
if(shift) {
destination = IntT(
(destination << shift) |
(destination >> (size - shift))
);
}
status.carry_flag = Status::FlagT(destination & 1);
break;
case Operation::RORb: case Operation::RORw: case Operation::RORl:
if(shift) {
destination = IntT(
(destination >> shift) |
(destination << (size - shift))
);
}
status.carry_flag = Status::FlagT(destination & top_bit<IntT>());
break;
}
@ -428,37 +448,56 @@ template <Operation operation, typename IntT, typename FlowController> void rox(
operation == Operation::ROXRb || operation == Operation::ROXRw || operation == Operation::ROXRl
);
const auto size = bit_size<IntT>();
constexpr auto size = bit_size<IntT>();
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 {
// TODO: if the value of the right operand is negative or is greater or equal to
// the number of bits in the promoted left operand, the behavior is undefined.
//
// i.e. for a long if shift >= 32,
// or size + 1 - shift >= 32, i.e. 1 - shift >= 0, 1 >= shift; i.e. shift <= 1
// ... the code below is undefined behaviour.
switch(operation) {
case Operation::ROXLb: case Operation::ROXLw: case Operation::ROXLl:
status.carry_flag = Status::FlagT((destination >> (size - shift)) & 1);
if(shift == bit_size<IntT>()) {
destination = IntT(
(status.extend_flag ? top_bit<IntT>() : 0) |
(destination >> 1)
);
} else if(shift == 1) {
destination = IntT(
(destination << 1) |
IntT(status.extend_flag ? 1 : 0)
);
} else {
destination = IntT(
(destination << shift) |
(IntT(status.extend_flag ? 1 : 0) << (shift - 1)) |
(destination >> (size + 1 - shift))
);
}
status.extend_flag = status.carry_flag;
break;
case Operation::ROXRb: case Operation::ROXRw: case Operation::ROXRl:
status.carry_flag = Status::FlagT(destination & (1 << (shift - 1)));
if(shift == bit_size<IntT>()) {
destination = IntT(
(status.extend_flag ? 1 : 0) |
(destination << 1)
);
} else if(shift == 1) {
destination = IntT(
(destination >> 1) |
(status.extend_flag ? top_bit<IntT>() : 0)
);
} else {
destination = IntT(
(destination >> shift) |
((status.extend_flag ? top_bit<IntT>() : 0) >> (shift - 1)) |
(destination << (size + 1 - shift))
);
}
status.extend_flag = status.carry_flag;
break;
}