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Fix integer overflows in rintersect() and optimize a bit of the logic

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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
This commit is contained in:
terminx 2019-06-25 11:28:40 +00:00 committed by Christoph Oelckers
parent 4ff7ec4a45
commit 2f9ca17507
1 changed files with 15 additions and 18 deletions
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33
source/build/src/engine.cpp
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@ -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;