commit 355e1d8d1d9935dbf902d81d53e410a5308045e4
Author:     Fabian Greffrath <fabian@greffrath.com>
AuthorDate: Mon Feb 18 12:33:55 2019 +0100
Commit:     GitHub <noreply@github.com>
CommitDate: Mon Feb 18 12:33:55 2019 +0100

    doom: fix initialization value of floor->crush in EV_BuildStairs() (#1137)

    * doom: fix initialization value of floor->crush in EV_BuildStairs()

    Dammit! I think I have made a mistake when I added initialization for
    the floor->type and floor->crush fields in EV_BuildStairs() in commit
    12b7676e7deb1e290be5128137014523227750a8.

    I was under the assumption that, because `10 != false`, it means the
    same as `true` -- but this is wrong. The code in question explicitly
    checks for `(floor->crush == true)` and not merely `(floor->crush)`,
    i.e. its value being unequal to zero.

    This will have lead to a desyncing TNT demo reported in
    https://www.doomworld.com/forum/topic/55558-final-doom-demos-complevel-4/?do=findComment&comment=1961738

    I need an extra pair of eyes this time. Guys, please double-check
    against the code in PrBoom+. The relevant piece of code starts here:
    https://github.com/coelckers/prboom-plus/blob/master/prboom2/src/p_floor.c#L797

    * add e6y's original comments to the initialization code
---
 src/doom/p_floor.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/doom/p_floor.c b/src/doom/p_floor.c
index c120d616..9468ed2a 100644
--- a/src/doom/p_floor.c
+++ b/src/doom/p_floor.c
@@ -30,6 +30,8 @@
 // Data.
 #include "sounds.h"

+//e6y
+#define STAIRS_UNINITIALIZED_CRUSH_FIELD_VALUE 10

 //
 // FLOORS
@@ -495,7 +497,10 @@ EV_BuildStairs
 	floor->floordestheight = height;
 	// Initialize
 	floor->type = lowerFloor;
-	floor->crush = true;
+	// e6y
+	// Uninitialized crush field will not be equal to 0 or 1 (true)
+	// with high probability. So, initialize it with any other value
+	floor->crush = STAIRS_UNINITIALIZED_CRUSH_FIELD_VALUE;

 	texture = sec->floorpic;

@@ -541,7 +546,10 @@ EV_BuildStairs
 		floor->floordestheight = height;
 		// Initialize
 		floor->type = lowerFloor;
-		floor->crush = true;
+		// e6y
+		// Uninitialized crush field will not be equal to 0 or 1 (true)
+		// with high probability. So, initialize it with any other value
+		floor->crush = STAIRS_UNINITIALIZED_CRUSH_FIELD_VALUE;
 		ok = 1;
 		break;
 	    }