65   DATA_TYPE *aX;  in presymmetry()  local
70   aX            = in+n2-3;  in presymmetry()
74     REG_TYPE  s0= aX[0];  in presymmetry()
75     REG_TYPE  s2= aX[2];  in presymmetry()
76     XPROD31( s0, s2, T[0], T[1], &aX[0], &aX[2] ); T+=step;  in presymmetry()
77     aX-=4;  in presymmetry()
78   }while(aX>=in+n4);  in presymmetry()
80     REG_TYPE  s0= aX[0];  in presymmetry()
81     REG_TYPE  s2= aX[2];  in presymmetry()
82     XPROD31( s0, s2, T[1], T[0], &aX[0], &aX[2] ); T-=step;  in presymmetry()
83     aX-=4;  in presymmetry()
84   }while(aX>=in);  in presymmetry()
86   aX            = in+n2-4;  in presymmetry()
90     REG_TYPE  ri0= aX[0];  in presymmetry()
91     REG_TYPE  ri2= aX[2];  in presymmetry()
95     XNPROD31( ro2, ro0, T[1], T[0], &aX[0], &aX[2] ); T+=step;  in presymmetry()
98     aX-=4;  in presymmetry()
100   }while(aX>=bX);  in presymmetry()