--- ray/src/rt/t_func.c	1989/04/11 13:30:33	1.5
+++ ray/src/rt/t_func.c	1989/10/05 07:23:20	1.7
@@ -43,6 +43,7 @@ register RAY  *r;
 	extern double  varvalue();
 	extern int  errno;
 	FVECT  disp;
+	double  d;
 	register XFORM  *mxf;
 	register int  i;
 	register char  **sa;
@@ -55,15 +56,11 @@ register RAY  *r;
 		mxf = (XFORM *)malloc(sizeof(XFORM));
 		if (mxf == NULL)
 			goto memerr;
-		mxf->fore.sca = 1.0;
-		setident4(mxf->fore.xfm);
 		if (xf(mxf->fore.xfm, &mxf->fore.sca,
 			m->oargs.nsargs-4, sa+4) != m->oargs.nsargs-4)
 			objerror(m, USER, "bad transform");
 		if (mxf->fore.sca < 0.0)
 			mxf->fore.sca = -mxf->fore.sca;
-		mxf->back.sca = 1.0;
-		setident4(mxf->back.xfm);
 		invxf(mxf->back.xfm, &mxf->back.sca,
 				m->oargs.nsargs-4, sa+4);
 		if (mxf->back.sca < 0.0)
@@ -84,8 +81,9 @@ register RAY  *r;
 	}
 	multv3(disp, disp, mxf->fore.xfm);
 	multv3(disp, disp, r->rofx);
+	d = 1.0 / (mxf->fore.sca * r->rofs);
 	for (i = 0; i < 3; i++)
-		r->pert[i] += disp[i] / (mxf->fore.sca * r->rofs);
+		r->pert[i] += disp[i] * d;
 	return;
 memerr:
 	error(SYSTEM, "out of memory in t_func");