From f3843a9a3acc90ab75710944225eddd50b40cd9e Mon Sep 17 00:00:00 2001
From: terminx <terminx@1a8010ca-5511-0410-912e-c29ae57300e0>
Date: Mon, 2 Apr 2018 22:00:23 +0000
Subject: [PATCH] Branchless sectorofwall_internal()

git-svn-id: https://svn.eduke32.com/eduke32@6794 1a8010ca-5511-0410-912e-c29ae57300e0
---
 source/build/include/build.h |  4 ++--
 source/build/src/engine.cpp  | 29 ++++++++++++++---------------
 2 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/source/build/include/build.h b/source/build/include/build.h
index 012257510..1616a77a7 100644
--- a/source/build/include/build.h
+++ b/source/build/include/build.h
@@ -1223,8 +1223,8 @@ int clipshape_idx_for_sprite(uspritetype const * const curspr, int curidx);
 
 void   alignceilslope(int16_t dasect, int32_t x, int32_t y, int32_t z);
 void   alignflorslope(int16_t dasect, int32_t x, int32_t y, int32_t z);
-int32_t   sectorofwall(int16_t theline);
-int32_t   sectorofwall_noquick(int16_t theline);
+int32_t sectorofwall(int16_t wallNum);
+int32_t sectorofwall_noquick(int16_t wallNum);
 int32_t   loopnumofsector(int16_t sectnum, int16_t wallnum);
 void setslope(int32_t sectnum, int32_t cf, int16_t slope);
 
diff --git a/source/build/src/engine.cpp b/source/build/src/engine.cpp
index e84f2def4..fc90a2c34 100644
--- a/source/build/src/engine.cpp
+++ b/source/build/src/engine.cpp
@@ -12473,39 +12473,38 @@ void completemirror(void)
 //
 // sectorofwall
 //
-static int32_t sectorofwall_internal(int16_t theline)
+static int32_t sectorofwall_internal(int16_t wallNum)
 {
-    int32_t gap = numsectors>>1, i = gap;
+    native_t gap = numsectors>>1, sectNum = gap;
 
     while (gap > 1)
     {
         gap >>= 1;
-        if (sector[i].wallptr < theline) i += gap; else i -= gap;
+        native_t const n = !!(sector[sectNum].wallptr < wallNum);
+        sectNum += (n ^ (n - 1)) * gap;
     }
-    while (sector[i].wallptr > theline) i--;
-    while (sector[i].wallptr+sector[i].wallnum <= theline) i++;
+    while (sector[sectNum].wallptr > wallNum) sectNum--;
+    while (sector[sectNum].wallptr + sector[sectNum].wallnum <= wallNum) sectNum++;
 
-    return i;
+    return sectNum;
 }
 
-int32_t sectorofwall(int16_t theline)
+int32_t sectorofwall(int16_t wallNum)
 {
-    if ((unsigned)theline >= (unsigned)numwalls)
+    if (EDUKE32_PREDICT_FALSE((unsigned)wallNum >= (unsigned)numwalls))
         return -1;
 
-    int i = wall[theline].nextwall;
-    if ((unsigned)i < MAXWALLS)
-        return wall[i].nextsector;
+    native_t const w = wall[wallNum].nextwall;
 
-    return sectorofwall_internal(theline);
+    return ((unsigned)w < MAXWALLS) ? wall[w].nextsector : sectorofwall_internal(wallNum);
 }
 
-int32_t sectorofwall_noquick(int16_t theline)
+int32_t sectorofwall_noquick(int16_t wallNum)
 {
-    if ((unsigned)theline >= (unsigned)numwalls)
+    if (EDUKE32_PREDICT_FALSE((unsigned) wallNum >= (unsigned) numwalls))
         return -1;
 
-    return sectorofwall_internal(theline);
+    return sectorofwall_internal(wallNum);
 }