From 8b4a87925b83af65ba8ebfe36949378d0d4ac81a Mon Sep 17 00:00:00 2001
From: helixhorned <helixhorned@1a8010ca-5511-0410-912e-c29ae57300e0>
Date: Sat, 22 Jun 2013 11:31:15 +0000
Subject: [PATCH] engine.c: apply "usual readability transformations" on
 inside() and comment it.

The main thing to note is the "half-open" nature of the x/y range checks.

git-svn-id: https://svn.eduke32.com/eduke32@3897 1a8010ca-5511-0410-912e-c29ae57300e0
---
 polymer/eduke32/build/src/build.c  | 20 +++++------
 polymer/eduke32/build/src/engine.c | 53 ++++++++++++++++++++----------
 2 files changed, 45 insertions(+), 28 deletions(-)

diff --git a/polymer/eduke32/build/src/build.c b/polymer/eduke32/build/src/build.c
index 215491834..c171054bd 100644
--- a/polymer/eduke32/build/src/build.c
+++ b/polymer/eduke32/build/src/build.c
@@ -1782,9 +1782,12 @@ static int32_t restore_highlighted_map(mapinfofull_t *mapinfo, int32_t forreal)
     // insert sprites
     for (i=0; i<mapinfo->numsprites; i++)
     {
-        int32_t sect = onumsectors+mapinfo->sprite[i].sectnum;
-        j = insertsprite(sect, mapinfo->sprite[i].statnum);
-        Bmemcpy(&sprite[j], &mapinfo->sprite[i], sizeof(spritetype));
+        const spritetype *srcspr = &mapinfo->sprite[i];
+        int32_t sect = onumsectors + srcspr->sectnum;
+
+        j = insertsprite(sect, srcspr->statnum);
+        Bassert(j >= 0);
+        Bmemcpy(&sprite[j], srcspr, sizeof(spritetype));
         sprite[j].sectnum = sect;
     }
 
@@ -8579,15 +8582,10 @@ int32_t fixspritesectors(void)
 
                 for (j=0; j<numsectors; j++)
                 {
-                    if (inside(dax,day, j) != 1)
-                        continue;
-
-                    if (cz <= sprite[i].z && sprite[i].z <= fz)
+                    if (cz <= sprite[i].z && sprite[i].z <= fz && inside(dax,day, j) == 1)
                     {
-                        if (fixmaponsave_sprites || (sprite[i].sectnum < 0 || sprite[i].sectnum >= numsectors))
+                        if (fixmaponsave_sprites || (unsigned)sprite[i].sectnum >= numsectors+0u)
                         {
-                            numfixedsprites++;
-
                             if (printfirsttime == 0)
                             {
                                 initprintf("--------------------\n");
@@ -8595,7 +8593,9 @@ int32_t fixspritesectors(void)
                             }
                             initprintf_nowarn("Changed sectnum of sprite #%d from %d to %d\n",
                                               i, TrackerCast(sprite[i].sectnum), j);
+
                             changespritesect(i, j);
+                            numfixedsprites++;
                         }
                         break;
                     }
diff --git a/polymer/eduke32/build/src/engine.c b/polymer/eduke32/build/src/engine.c
index a664e1f95..f16a9bd91 100644
--- a/polymer/eduke32/build/src/engine.c
+++ b/polymer/eduke32/build/src/engine.c
@@ -11385,28 +11385,45 @@ int32_t clipinsideboxline(int32_t x, int32_t y, int32_t x1, int32_t y1, int32_t
 //
 int32_t inside(int32_t x, int32_t y, int16_t sectnum)
 {
-    walltype *wal;
-    int32_t i, x1, y1, x2, y2;
-    uint32_t cnt;
-
-    if (sectnum < 0 || sectnum >= numsectors)
-        return -1;
-
-    cnt = 0;
-    wal = &wall[sector[sectnum].wallptr];
-    i = sector[sectnum].wallnum;
-    do
+    if (sectnum >= 0 && sectnum < numsectors)
     {
-        y1 = wal->y-y; y2 = wall[wal->point2].y-y;
-        if ((y1^y2) < 0)
+        uint32_t cnt = 0;
+        walltype *wal = &wall[sector[sectnum].wallptr];
+        int32_t i = sector[sectnum].wallnum;
+
+        do
         {
-            x1 = wal->x-x; x2 = wall[wal->point2].x-x;
-            if ((x1^x2) >= 0) cnt ^= x1; else cnt ^= (x1*y2-x2*y1)^y2;
+            // Get the y components of the [tested point]-->[wall point{1,2}]
+            // vectors.
+            const int32_t y1 = wal->y - y;
+            const int32_t y2 = wall[wal->point2].y - y;
+
+            // If their signs differ[*], ...
+            //
+            // [*] where '-' corresponds to <0 and '+' corresponds to >=0.
+            // Equivalently, the branch is taken iff
+            //   y1 != y2 AND y_m <= wal->y < y_M,
+            // where y_m := min(y1, y2) and y_M := max(y1, y2).
+            if ((y1^y2) < 0)
+            {
+                // ... get the x components.
+                const int32_t x1 = wal->x - x;
+                const int32_t x2 = wall[wal->point2].x - x;
+
+                if ((x1^x2) >= 0)
+                    cnt ^= x1;
+                else
+                    cnt ^= (x1*y2-x2*y1)^y2;
+            }
+
+            wal++; i--;
         }
-        wal++; i--;
+        while (i);
+
+        return cnt>>31;
     }
-    while (i);
-    return(cnt>>31);
+
+    return -1;
 }
 
 int32_t __fastcall getangle(int32_t xvect, int32_t yvect)