A fix for tomath repr right shifts

fix_rshift-nqp_bigint_ops

/* Cargo-culted fix for right shift issues in nqp_bigint.ops. */

/* This could be done better in a way that doesn't dirty so much write cache
   for huge shifts/values, since the results are calculatable without actually
   performing additions across the whole number. */

inline op nqp_bigint_shr(out PMC, invar PMC, in INT, invar PMC) :base_core {
    mp_int b;
    mp_int *a = get_bigint(interp, $2);

    mp_init((&b));
    mp_copy(a,(&b));

    if (MP_NEG == SIGN(a)) {
        /* deal with two's complement one-offness */
        mp_add_d((&b),1,(&b));
    }

    $1 = REPR($4)->allocate(interp, STABLE($4));
    REPR($1)->initialize(interp, STABLE($1), OBJECT_BODY($1));
    mp_div_2d((&b), $3, (&b), NULL);

    if (MP_NEG == SIGN(a)) {
        mp_sub_d((&b),1,(&b));
    }
    mp_copy((&b),get_bigint(interp, $1));

    mp_clear((&b));
}