**

VALUE
rb_big_pow(VALUE x, VALUE y)
{
    double d;
    SIGNED_VALUE yy;

    if (y == INT2FIX(0)) return INT2FIX(1);
    switch (TYPE(y)) {
      case T_FLOAT:
        d = RFLOAT_VALUE(y);
        if ((!RBIGNUM_SIGN(x) && !BIGZEROP(x)) && d != round(d))
            return rb_funcall(rb_complex_raw1(x), rb_intern("**"), 1, y);
        break;

      case T_BIGNUM:
        rb_warn("in a**b, b may be too big");
        d = rb_big2dbl(y);
        break;

      case T_FIXNUM:
        yy = FIX2LONG(y);

        if (yy < 0)
            return rb_funcall(rb_rational_raw1(x), rb_intern("**"), 1, y);
        else {
            VALUE z = 0;
            SIGNED_VALUE mask;
            const long xlen = RBIGNUM_LEN(x) - 1;
            const long xbits = ffs(RBIGNUM_DIGITS(x)[xlen]) + SIZEOF_BDIGITS*BITSPERDIG*xlen;
            const long BIGLEN_LIMIT = BITSPERDIG*1024*1024;

            if ((xbits > BIGLEN_LIMIT) || (xbits * yy > BIGLEN_LIMIT)) {
                rb_warn("in a**b, b may be too big");
                d = (double)yy;
                break;
            }
            for (mask = FIXNUM_MAX + 1; mask; mask >>= 1) {
                if (z) z = bigsqr(z);
                if (yy & mask) {
                    z = z ? bigtrunc(bigmul0(z, x)) : x;
                }
            }
            return bignorm(z);
        }
        /* NOTREACHED */
        break;

      default:
        return rb_num_coerce_bin(x, y, rb_intern("**"));
    }
    return DBL2NUM(pow(rb_big2dbl(x), d));
}