[Bug 110435] fp64 division gives imprecise results

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110435

Kenneth Graunke <kenneth at whitecape.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #6 from Kenneth Graunke <kenneth at whitecape.org> ---
Thanks for the fix!  Fixed by:

commit 974c4d679c23373dbed386c696e3e3bc1bfa23ae
Author: Ruslan Kabatsayev <b7.10110111 at gmail.com>
Date:   Sat May 11 14:04:36 2019 +0300

    nir: Fix wrong sign in lower_rcp

    The nested fma calls were supposed to implement

    x_new = x + x * (1 - x*src),

    but instead current code is equivalent to

    x_new = x - x * (1 - x*src).

    The result is that Newton-Raphson steps don't improve precision at all.
    This patch fixes this problem.

    Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110435
    Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

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