From 2f9ca1750743f59c31dcb4877bb22923ef7badb7 Mon Sep 17 00:00:00 2001
From: terminx <terminx@1a8010ca-5511-0410-912e-c29ae57300e0>
Date: Tue, 25 Jun 2019 11:28:40 +0000
Subject: [PATCH] Fix integer overflows in rintersect() and optimize a bit of
 the logic

Some of the variable initialization ordering may look counterintuitive at first, but it's intended to avoid read-after-write memory access penalties.

git-svn-id: https://svn.eduke32.com/eduke32@7701 1a8010ca-5511-0410-912e-c29ae57300e0
---
 source/build/src/engine.cpp | 33 +++++++++++++++------------------
 1 file changed, 15 insertions(+), 18 deletions(-)

diff --git a/source/build/src/engine.cpp b/source/build/src/engine.cpp
index 2932d4eac..6f7366ad4 100644
--- a/source/build/src/engine.cpp
+++ b/source/build/src/engine.cpp
@@ -7563,38 +7563,35 @@ int32_t lintersect(const int32_t originX, const int32_t originY, const int32_t o
 //
 // returns: -1 if didn't intersect, coefficient (x3--x4 fraction)<<16 else
 int32_t rintersect(int32_t x1, int32_t y1, int32_t z1,
-                   int32_t vx_, int32_t vy_, int32_t vz,
+                   int32_t vx, int32_t vy, int32_t vz,
                    int32_t x3, int32_t y3, int32_t x4, int32_t y4,
                    int32_t *intx, int32_t *inty, int32_t *intz)
 {
     //p1 towards p2 is a ray
-    int64_t topt, topu, t;
 
-    const int64_t vx=vx_, vy=vy_;
-    const int64_t x34=x3-x4, y34=y3-y4;
-    const int64_t bot = vx*y34 - vy*x34;
+    int64_t const x34=x3-x4, y34=y3-y4;
+    int64_t const x31=x3-x1, y31=y3-y1;
+
+    int64_t const bot  = vx*y34 - vy*x34;
+    int64_t const topt = x31*y34 - y31*x34;
 
     if (bot == 0)
         return -1;
-    else if (bot > 0)
-    {
-        int64_t x31=x3-x1, y31 = y3-y1;
-        topt = x31*y34 - y31*x34; if (topt < 0) return -1;
-        topu = vx*y31 - vy*x31; if (topu < 0 || topu >= bot) return -1;
-    }
-    else
-    {
-        int32_t x31=x3-x1, y31=y3-y1;
-        topt = x31*y34 - y31*x34; if (topt > 0) return -1;
-        topu = vx*y31 - vy*x31; if (topu > 0 || topu <= bot) return -1;
-    }
 
-    t = (topt<<16)/bot;
+    int64_t const topu = vx*y31 - vy*x31;
+
+    if (bot > 0 && (topt < 0 || topu < 0 || topu >= bot))
+        return -1;
+    else if (bot < 0 && (topt > 0 || topu > 0 || topu <= bot))
+        return -1;
+
+    int64_t t = (topt<<16)/bot;
     *intx = x1 + ((vx*t)>>16);
     *inty = y1 + ((vy*t)>>16);
     *intz = z1 + ((vz*t)>>16);
 
     t = (topu<<16)/bot;
+
     Bassert((unsigned)t < 65536);
 
     return t;