6502/erc-c
1
0
Fork 0
mirror of https://github.com/pevans/erc-c.git synced 2025-01-18 10:30:37 +00:00
Code Issues Projects Releases Wiki Activity

Also check the N flag (i.e. set it to zero)

Browse Source
This commit is contained in:
Peter Evans 2018-02-15 13:01:58 -06:00
parent e415b3e490
commit 067c0cea2f
1 changed files with 5 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
src/mos6502.bits.c
View File

@ -97,8 +97,11 @@ DEFINE_INST(lsr)
{
SET_RESULT(oper >> 1);
// Set ZERO if it should apply
mos6502_modify_status(cpu, MOS_ZERO, oper, result);
// Set ZERO if it should apply; also inspect the NEGATIVE flag, but
// note that doing so will have the effect of _always_ unsetting the
// N flag, because literally any byte value shifted right will
// immediately lose the sign bit and be non-negative.
mos6502_modify_status(cpu, MOS_NZ, oper, result);
// However, we handle carry a bit differently here. The carry bit
// should be 1 if oper & 0x1; that is, when we shift right, we want