6502/CLK
1
0
Fork 0
mirror of https://github.com/TomHarte/CLK.git synced 2025-01-11 08:30:55 +00:00
Code Issues Projects Releases Wiki Activity

Fixed overflow for 8-bit decrementing.

Browse Source
This commit is contained in:
Thomas Harte 2017-05-25 21:23:38 -04:00
parent e4e71a1e5f
commit 598be24644
1 changed files with 5 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
Processors/Z80/Z80.hpp
View File

@ -726,9 +726,9 @@ template <class T> class Processor: public MicroOpScheduler<MicroOp> {
uint8_t value = *(uint8_t *)operation->source;
int result = value - 1;
// with an increment, overflow occurs if the sign changes from
// positive to negative
int overflow = (value ^ result) & ~value;
// with a decrement, overflow occurs if the sign changes from
// negative to positive
int overflow = (value ^ result) & value;
int half_result = (value&0xf) - 1;
*(uint8_t *)operation->source = (uint8_t)result;
@ -918,7 +918,7 @@ template <class T> class Processor: public MicroOpScheduler<MicroOp> {
@returns The current value of the flags register.
*/
uint8_t get_flags() {
return
uint8_t result =
(sign_result_ & Flag::Sign) |
(zero_result_ ? 0 : Flag::Zero) |
(bit5_result_ & Flag::Bit5) |
@ -927,6 +927,7 @@ template <class T> class Processor: public MicroOpScheduler<MicroOp> {
parity_overflow_flag_ |
subtract_flag_ |
carry_flag_;
return result;
}
/*!