From 056dced9238126db034cf3542c9e0969d105a0d0 Mon Sep 17 00:00:00 2001
From: Robert <Robbbert@users.noreply.github.com>
Date: Mon, 17 Nov 2014 22:17:48 +1100
Subject: [PATCH] (MESS) gamecom : fixed calculator

---
 src/emu/cpu/sm8500/sm85ops.h | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/emu/cpu/sm8500/sm85ops.h b/src/emu/cpu/sm8500/sm85ops.h
index 06251975c26..6c9c45a7b07 100644
--- a/src/emu/cpu/sm8500/sm85ops.h
+++ b/src/emu/cpu/sm8500/sm85ops.h
@@ -63,8 +63,8 @@
 			} \
 			break; \
 		case 0xC0: \
-			s2 = mem_readword( sm8500_b2w[r1 & 0x07] ); \
-			mem_writeword( sm8500_b2w[r1 & 0x07], s2 - 1 ); \
+			s2 = mem_readword( sm8500_b2w[r1 & 0x07])-1; \
+			mem_writeword( sm8500_b2w[r1 & 0x07], s2 ); \
 			break; \
 		} \
 		r2 = r1; \
@@ -1270,12 +1270,16 @@ case 0x59:  /* Invalid - 2? cycles - Flags affected: --------? */
 	mycycles += 2;
 	break;
 case 0x5A:  /* unk5A - 7,8,12,9,8 cycles */
-logerror( "%04X: unk%02x\n", m_PC-1,op );
-	ARG_ad16;
+	logerror( "%04X: unk%02x\n", m_PC-1,op );
+/* NOTE: This unknown command is used in the calculator as a compare instruction
+       at 0x493A and 0x4941, we set the flags on the 3rd byte, although its real
+       function remains a mystery */
+	ARG_iR;
+	OP_CMP8( 0, r1 );
 	mycycles += 7;
 	break;
 case 0x5B:  /* unk5B - 6,7,11,8,7 cycles */
-logerror( "%04X: unk%02x\n", m_PC-1,op );
+	logerror( "%04X: unk%02x\n", m_PC-1,op );
 /* NOTE: This unknown command is used in several carts, the code below allows those carts to boot */
 	ARG_iR;
 	r1 = r2 & 7;