From b24be4f52620d01fd2928d8afddd9fe884b392ed Mon Sep 17 00:00:00 2001
From: Filippos Karapetis
Date: Wed, 27 Jan 2010 12:13:39 +0000
Subject: Added support of the subtraction of two pointers, when they got the
 same segment. This operation will yield a number, like in C, and it's used by
 script 385 in Castle of Dr. Brain (the hangman script). Fixes exiting room
 360 (the puzzle room) in Castle of Dr. Brain

svn-id: r47595
---
 engines/sci/engine/vm.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

(limited to 'engines/sci/engine')

diff --git a/engines/sci/engine/vm.cpp b/engines/sci/engine/vm.cpp
index e921d0f8fc..3d320d485c 100644
--- a/engines/sci/engine/vm.cpp
+++ b/engines/sci/engine/vm.cpp
@@ -763,7 +763,7 @@ void run_vm(EngineState *s, int restoring) {
 
 		case 0x02: // sub
 			r_temp = POP32();
-			if (r_temp.segment || s->r_acc.segment) {
+			if (r_temp.segment != s->r_acc.segment) {
 				reg_t r_ptr = NULL_REG;
 				int offset;
 				// Pointer arithmetics!
@@ -783,8 +783,11 @@ void run_vm(EngineState *s, int restoring) {
 
 				s->r_acc = pointer_add(s, r_ptr, -offset);
 
-			} else
+			} else {
+				// We can subtract numbers, or pointers with the same segment,
+				// an operation which will yield a number like in C
 				s->r_acc = make_reg(0, r_temp.offset - s->r_acc.offset);
+			}
 			break;
 
 		case 0x03: // mul
-- 
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