diff -urN rt_v59/rt.c rt_v60/rt.c
--- rt_v59/rt.c	2018-06-11 22:28:29.000000000 +0900
+++ rt_v60/rt.c	2018-07-11 20:37:30.000000000 +0900
@@ -159,7 +159,7 @@
 	}
 }
 
-void
+int
 reflact_v(struct rtd *rtd, double *nv, double *eyev, double ang_nv_eyev, double *ret_v)
 {
 	double density = rtd->density;
@@ -168,7 +168,7 @@
 
 	if(density == 1 || fabs(ang_nv_eyev) == 1 || ang_nv_eyev == 0){
 		v_set(ret_v, eyev);
-		return;
+		return 1;
 	}
 	v_mul(nv, ang_nv_eyev, cos_v);
 	v_sub(eyev, cos_v, sin_v);
@@ -178,11 +178,14 @@
 	v_mul(sin_v, density, r_sin_v);
 
 	sin_len2 = dot( r_sin_v, r_sin_v );
-	sin_len2 = sin_len2 < 1 ? sin_len2 : 1;
+	if(sin_len2 > 1){
+		return 0;
+	}
 	cos_len = sqrt( 1 - sin_len2 );
 	v_mul(cos_v, cos_len / len1( cos_v ), r_cos_v);
 	v_add(r_sin_v, r_cos_v, ret_v);
 	unit(ret_v, ret_v);
+	return 1;
 }
 
 void
@@ -200,7 +203,9 @@
 	if(reflact ==  0){
 		return;
 	}
-	reflact_v(rtd, nv, eyev, ang_nv_eyev, ref_v);
+	if(reflact_v(rtd, nv, eyev, ang_nv_eyev, ref_v) == 0){
+		return;
+	}
 	line_new(&ref_l, crsp, ref_v);
 
 	get_col(&ref_l, sec, nest_rate * reflact, idx, col);
diff -urN rt_v59/ut.c rt_v60/ut.c
--- rt_v59/ut.c	2018-06-15 21:58:23.000000000 +0900
+++ rt_v60/ut.c	2018-07-11 20:36:46.000000000 +0900
@@ -235,4 +235,6 @@
 	}
 }
 
+int dbg_enable = 0;
+
 /* EOF */
diff -urN rt_v59/ut.h rt_v60/ut.h
--- rt_v59/ut.h	2018-06-15 21:58:23.000000000 +0900
+++ rt_v60/ut.h	2018-07-11 20:36:46.000000000 +0900
@@ -59,4 +59,7 @@
 int ut_itbl_get_v(struct ut_itbl *t, int i);
 void ut_itbl_free(struct ut_itbl *t);
 
+extern int dbg_enable;
+#define DBG(...) do{ if(dbg_enable) fprintf(stderr, __VA_ARGS__); }while(0)
+
 #endif