one-bit estimate of Reg*Sha

Dear PARI-dev,

For number fields under GRH it is possible to compute the product h*R
analytically to a fixed floating point precision in polynomial time.

Is there a similar result for the product Reg Sha of a rank-1 elliptic curves ?
That is, computing lfun(E,1,1) with very low precision.

I just need B such that B <= Reg Sha <= 2*B.

Cheers,
Bill