From 2ac02d91c226930885cbec402dbdca8a98a970c4 Mon Sep 17 00:00:00 2001
From: folkert van heusden <mail@vanheusden.com>
Date: Sun, 20 Mar 2022 21:20:15 +0100
Subject: [PATCH] restructured ASH & limit to -32...31

---
 cpu.cpp | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/cpu.cpp b/cpu.cpp
index c04b16d..ac3365d 100644
--- a/cpu.cpp
+++ b/cpu.cpp
@@ -479,21 +479,20 @@ bool cpu::additional_double_operand_instructions(const uint16_t instr)
 		case 2: { // ASH
 				int16_t  R     = getRegister(reg), oldR = R;
 				uint16_t a     = getGAMAddress(dst_mode, dst_reg, false, false);
-				int16_t  shift = b->read(a, false);
+				int16_t  shift = b->read(a, false) & 077; // mask of lower 6 bit
 
-				if (shift > 0) {
+				if (shift == 0)
+					setPSW_c(false);
+				else if (shift < 32) {
 					R <<= shift - 1;
 					setPSW_c(R & 0x8000);
 					R <<= 1;
 				}
-				else if (shift < 0) {
-					R >>= -(shift + 1);
+				else {
+					R >>= 64 - shift - 1;
 					setPSW_c(R & 1);
 					R >>= 1;
 				}
-				else {
-					setPSW_c(false);
-				}
 
 				setPSW_n(R < 0);
 				setPSW_z(R == 0);