As defined in Power 3.0 section 4.4.4 "Underflow Exception",
a tiny result is detected before rounding.
Fixes: https://bugs.launchpad.net/qemu/+bug/1841491
Reported-by: Paul Clarke <pc@us.ibm.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20190827020013.27154-1-richard.henderson@linaro.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>