--- ray/src/common/dircode.c	2019/05/14 17:21:50	2.9
+++ ray/src/common/dircode.c	2020/03/04 02:55:43	2.11
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char RCSid[] = "$Id: dircode.c,v 2.9 2019/05/14 17:21:50 greg Exp $";
+static const char RCSid[] = "$Id: dircode.c,v 2.11 2020/03/04 02:55:43 greg Exp $";
 #endif
 /*
  * Compute a 4-byte direction code (externals defined in rtmath.h).
@@ -9,7 +9,7 @@ static const char RCSid[] = "$Id: dircode.c,v 2.9 2019
 
 #include "rtmath.h"
 
-#define	DCSCALE		11585.2		/* (1<<13)*sqrt(2) */
+#define	DCSCALE		11584.7		/* (1<<13)*sqrt(2) - .5 */
 #define FXNEG		01
 #define FYNEG		02
 #define FZNEG		04
@@ -28,10 +28,10 @@ encodedir(FVECT dv)		/* encode a normalized direction 
 
 	for (i = 0; i < 3; i++)
 		if (dv[i] < 0.) {
-			cd[i] = (int)(dv[i] * -DCSCALE);
+			cd[i] = (int)(dv[i] * -DCSCALE + .5);
 			dc |= FXNEG<<i;
 		} else
-			cd[i] = (int)(dv[i] * DCSCALE);
+			cd[i] = (int)(dv[i] * DCSCALE + .5);
 	if (!(cd[0] | cd[1] | cd[2]))
 		return(0);		/* zero normal */
 	if (cd[0] <= cd[1]) {
@@ -94,8 +94,8 @@ decodedir(FVECT dv, int32 dc)	/* decode a normalized d
 		dv[0] = dv[1] = dv[2] = 0.;
 		return;
 	}
-	d1 = ((dc>>F1SFT & FMASK)+.5)*(1./DCSCALE);
-	d2 = ((dc>>F2SFT & FMASK)+.5)*(1./DCSCALE);
+	d1 = (dc>>F1SFT & FMASK)*(1./DCSCALE);
+	d2 = (dc>>F2SFT & FMASK)*(1./DCSCALE);
 	der = sqrt(1. - d1*d1 - d2*d2);
 	dv[itab[ndx][0]] = d1;
 	dv[itab[ndx][1]] = d2;
@@ -111,6 +111,9 @@ double
 dir2diff(int32 dc1, int32 dc2)	/* approx. radians^2 between directions */
 {
 	FVECT	v1, v2;
+
+	if (dc1 == dc2)
+		return 0.;
 
 	decodedir(v1, dc1);
 	decodedir(v2, dc2);