From 78069349601edfec9068d24f24ef01cf7d2e06b4 Mon Sep 17 00:00:00 2001
From: SkyratBot <59378654+SkyratBot@users.noreply.github.com>
Date: Sat, 14 May 2022 16:24:18 +0200
Subject: [PATCH] [MIRROR] Protect against floating-point inaccuracy in log()
 [MDB IGNORE] (#13600)

* Protect against floating-point inaccuracy in log() (#66875)

This was causing issues with indexing icon slots (the main user of TOBITSHIFT). See BeeStation/BeeStation-Hornet#6842 for more details.
Probably fixes #66197 and fixes #65652. (In all my tests, I could never get anything to show in suit_storage, whereas those bugs are reporting intermittent issues.)
Originally made for BeeStation/BeeStation-Hornet#6842 (which also affects TG).

* Protect against floating-point inaccuracy in log()

Co-authored-by: David Walker <d0sboots@gmail.com>
---
 code/__DEFINES/maths.dm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/code/__DEFINES/maths.dm b/code/__DEFINES/maths.dm
index b4de855bef9..cd75a7a0172 100644
--- a/code/__DEFINES/maths.dm
+++ b/code/__DEFINES/maths.dm
@@ -117,7 +117,8 @@
 #define TORADIANS(degrees) ((degrees) * 0.0174532925)
 
 /// Gets shift x that would be required the bitflag (1<<x)
-#define TOBITSHIFT(bit) ( log(2, bit) )
+/// We need the round because log has floating-point inaccuracy, and if we undershoot at all on list indexing we'll get the wrong index.
+#define TOBITSHIFT(bit) ( round(log(2, bit), 1) )
 
 // Will filter out extra rotations and negative rotations
 // E.g: 540 becomes 180. -180 becomes 180.