__kernel_tan
extern double __kernel_tan __P((double,double,int));
if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1);
return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even
t = - __kernel_tan(hi, lo, -1);
t = __kernel_tan(hi, lo, 1);