fix indirect JMP bug where the high byte does not increment out of page

https://old.reddit.com/r/EmuDev/comments/15plfes/having_an_issue_with_nestest_on_my_6502_emulator/jvyck7k/

With this, it seems that all official opcodes run as nestest expects.
Now, it's the unofficial opcodes that need to be implemented.

1 files changed, 4 insertions, 3 deletions

diff --git a/cpu.c b/cpu.c
index 51ab824..a2fea28 100644
--- a/cpu.c
+++ b/cpu.c
@@ -196,7 +196,7 @@ opcode_mem(enum addressing_mode mode)
                 val = arg + regs.y;
                 break;
         case AM_IND:
-                val = peek16(arg);
+                val = peek(arg) | (peek(((arg + 1) & 0xFF) | (arg & 0xFF00)) << 8);
                 break;
         case AM_IND_X:
                 val = peek((arg + regs.x) % 256) + peek((arg + regs.x + 1) % 256) * 256;
@@ -1308,9 +1308,10 @@ interpret(void)
                 case 0x6c:
                         mode = AM_IND;
                         mem = peek16(regs.pc);
-                        deref = peek(mem);
+                        deref = peek16(mem);
                         arg = opcode_mem(mode);
-                        jmp(deref);
+                        deref = arg;
+                        jmp(arg);
                         cycles += 6;
                         printf("JMP");
                         break;