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Fixed overflow bug in m68k

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transistor 2021-11-13 10:54:59 -08:00
parent d472b95d9d
commit e0d863a845
1 changed files with 18 additions and 24 deletions
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42
src/cpus/m68k/execute.rs
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@ -173,7 +173,7 @@ impl M68k {
let value = self.get_target_value(system, src, size)?;
let existing = self.get_target_value(system, dest, size)?;
let (result, carry) = overflowing_add_sized(existing, value, size);
let (_, overflow) = overflowing_add_signed_sized(existing, value, size);
let overflow = get_add_overflow(existing, value, result, size);
self.set_compare_flags(result, size, carry, overflow);
self.set_flag(Flags::Extend, carry);
self.set_target_value(system, dest, result, size)?;
@ -328,14 +328,14 @@ impl M68k {
let value = self.get_target_value(system, src, size)?;
let existing = self.get_target_value(system, dest, size)?;
let (result, carry) = overflowing_sub_sized(existing, value, size);
let (_, overflow) = overflowing_add_signed_sized(existing, value, size);
let overflow = get_sub_overflow(existing, value, result, size);
self.set_compare_flags(result, size, carry, overflow);
},
Instruction::CMPA(src, reg, size) => {
let value = sign_extend_to_long(self.get_target_value(system, src, size)?, size) as u32;
let existing = *self.get_a_reg_mut(reg);
let (result, carry) = overflowing_sub_sized(existing, value, Size::Long);
let (_, overflow) = overflowing_add_signed_sized(existing, value, size);
let overflow = get_sub_overflow(existing, value, result, size);
self.set_compare_flags(result, Size::Long, carry, overflow);
},
Instruction::DBcc(cond, reg, offset) => {
@ -551,9 +551,10 @@ impl M68k {
Instruction::NEG(target, size) => {
let original = self.get_target_value(system, target, size)?;
let (result, overflow) = overflowing_sub_signed_sized(0, original, size);
let carry = result != 0;
self.set_target_value(system, target, result, size)?;
self.set_compare_flags(result, size, result != 0, overflow);
self.set_flag(Flags::Extend, self.get_flag(Flags::Carry));
self.set_compare_flags(result, size, carry, overflow);
self.set_flag(Flags::Extend, carry);
},
//Instruction::NEGX(Target, Size) => {
//},
@ -645,7 +646,7 @@ impl M68k {
let value = self.get_target_value(system, src, size)?;
let existing = self.get_target_value(system, dest, size)?;
let (result, carry) = overflowing_sub_sized(existing, value, size);
let (_, overflow) = overflowing_add_signed_sized(existing, value, size);
let overflow = get_sub_overflow(existing, value, result, size);
self.set_compare_flags(result, size, carry, overflow);
self.set_flag(Flags::Extend, carry);
self.set_target_value(system, dest, result, size)?;
@ -1100,23 +1101,6 @@ fn overflowing_sub_sized(operand1: u32, operand2: u32, size: Size) -> (u32, bool
}
}
fn overflowing_add_signed_sized(operand1: u32, operand2: u32, size: Size) -> (u32, bool) {
match size {
Size::Byte => {
let (result, overflow) = (operand1 as i8).overflowing_add(operand2 as i8);
(result as u32, overflow)
},
Size::Word => {
let (result, overflow) = (operand1 as i16).overflowing_add(operand2 as i16);
(result as u32, overflow)
},
Size::Long => {
let (result, overflow) = (operand1 as i32).overflowing_add(operand2 as i32);
(result as u32, overflow)
},
}
}
fn overflowing_sub_signed_sized(operand1: u32, operand2: u32, size: Size) -> (u32, bool) {
match size {
Size::Byte => {
@ -1187,7 +1171,7 @@ fn set_value_sized(addr: &mut u32, value: u32, size: Size) {
}
}
fn get_overflow(operand1: u32, operand2: u32, result: u32, size: Size) -> bool {
fn get_add_overflow(operand1: u32, operand2: u32, result: u32, size: Size) -> bool {
let msb1 = get_msb(operand1, size);
let msb2 = get_msb(operand2, size);
let msb_res = get_msb(result, size);
@ -1195,10 +1179,19 @@ fn get_overflow(operand1: u32, operand2: u32, result: u32, size: Size) -> bool {
(msb1 && msb2 && !msb_res) || (!msb1 && !msb2 && msb_res)
}
fn get_sub_overflow(operand1: u32, operand2: u32, result: u32, size: Size) -> bool {
let msb1 = get_msb(operand1, size);
let msb2 = !get_msb(operand2, size);
let msb_res = get_msb(result, size);
(msb1 && msb2 && !msb_res) || (!msb1 && !msb2 && msb_res)
}
fn get_twos_complement(value: u32, size: Size) -> u32 {
get_value_sized(!value + 1, size)
}
#[inline(always)]
fn get_msb(value: u32, size: Size) -> bool {
match size {
Size::Byte => (value & 0x00000080) != 0,
@ -1207,6 +1200,7 @@ fn get_msb(value: u32, size: Size) -> bool {
}
}
#[inline(always)]
fn get_msb_mask(value: u32, size: Size) -> u32 {
match size {
Size::Byte => value & 0x00000080,