--- ray/src/rt/source.c	1989/06/13 08:20:22	1.11
+++ ray/src/rt/source.c	1989/06/13 10:57:52	1.12
@@ -27,6 +27,7 @@ static char SCCSid[] = "$SunId$ LBL";
 
 extern double  dstrsrc;			/* source distribution amount */
 extern double  shadthresh;		/* relative shadow threshold */
+extern double  shadcert;		/* shadow testing certainty */
 
 SRCREC  *source = NULL;			/* our list of sources */
 int  nsources = 0;			/* the number of sources */
@@ -301,9 +302,11 @@ RAY  *r;			/* ray that hit surface */
 int  (*f)();			/* direct component coefficient function */
 char  *p;			/* data for f */
 {
+	extern double  pow();
 	register int  sn;
 	register CONTRIB  *srccnt;
 	register CNTPTR  *cntord;
+	int  nshadcheck, ncnts;
 	double  prob, ourthresh, hwt, test2, hit2;
 	RAY  sr;
 
@@ -311,6 +314,8 @@ char  *p;			/* data for f */
 	cntord = (CNTPTR *)malloc(nsources*sizeof(CNTPTR));
 	if (srccnt == NULL || cntord == NULL)
 		error(SYSTEM, "out of memory in direct");
+						/* compute number to check */
+	nshadcheck = pow((double)nsources, shadcert) + .5;
 						/* modify threshold */
 	ourthresh = shadthresh / r->rweight;
 						/* potential contributions */
@@ -339,11 +344,27 @@ char  *p;			/* data for f */
 	}
 						/* sort contributions */
 	qsort(cntord, nsources, sizeof(CNTPTR), cntcmp);
-	hit2 = 0.5; test2 = 1.0;		/* start with prob=.5 */
+                                                /* find last */
+        sn = 0; ncnts = nsources;
+        while (sn < ncnts-1) {
+                register int  m;
+                m = (sn + ncnts) >> 1;
+                if (cntord[m].brt > 0.0)
+                        sn = m;
+                else
+                        ncnts = m;
+        }
+                                                /* accumulate tail */
+        for (sn = ncnts-1; sn > 0; sn--)
+                cntord[sn-1].brt += cntord[sn].brt;
+						/* start with prob=.5 */
+	hit2 = 0.5; test2 = 1.0;
 						/* test for shadows */
-	for (sn = 0; sn < nsources; sn++) {
+	for (sn = 0; sn < ncnts; sn++) {
 						/* check threshold */
-		if (cntord[sn].brt <= ourthresh*bright(r->rcol))
+		if ((sn+nshadcheck>=ncnts ? cntord[sn].brt :
+				cntord[sn].brt-cntord[sn+nshadcheck].brt) <
+				ourthresh*bright(r->rcol))
 			break;
 						/* get statistics */
 		hwt = (double)source[cntord[sn].sno].nhits /
@@ -375,23 +396,17 @@ char  *p;			/* data for f */
 					/* weighted hit rate */
 	hwt = hit2 / test2;
 #ifdef DEBUG
-	{
-		int  ntested = sn;
+	sprintf(errmsg, "%d tested, %d untested, %f hit rate\n",
+			sn, ncnts-sn, hwt);
+	eputs(errmsg);
 #endif
 					/* add in untested sources */
-	for ( ; sn < nsources; sn++) {
-		if (cntord[sn].brt <= 0.0)
-			break;
+	for ( ; sn < ncnts; sn++) {
 		prob = hwt * (double)source[cntord[sn].sno].nhits /
 				(double)source[cntord[sn].sno].ntests;
 		scalecolor(srccnt[cntord[sn].sno].val, prob);
 		addcolor(r->rcol, srccnt[cntord[sn].sno].val);
 	}
-#ifdef DEBUG
-	fprintf(stderr, "%d tested, %d untested, %f hit rate\n",
-			ntested, sn-ntested, hwt);
-	}
-#endif
 		
 	free(srccnt);
 	free(cntord);