From 9febc11af9a8a5b227ddaeda4798ae0ef52bd644 Mon Sep 17 00:00:00 2001 From: Chia-I Wu Date: Thu, 28 Apr 2022 14:25:36 -0700 Subject: [PATCH] util: Keep quiet NaNs quiet when converting to half float. We don't want to be throwing exceptions and changing float values later by emitting a signaling binary16 nan. If we don't do this, then when we convert back to f32 in NIR constant expression evaluation, the signaling NaN can end up giving NaN for fmax(NaN, 0.0), instead of 0.0. Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/5933 Cc: mesa-stable Reviewed-by: Emma Anholt Reviewed-by: Jason Ekstrand Part-of: (cherry picked from commit 27e33d5c963f13a47c4b9276378db913d8ecb189) --- .pick_status.json | 2 +- src/util/half_float.c | 8 ++++++-- src/util/softfloat.c | 7 ++++++- 3 files changed, 13 insertions(+), 4 deletions(-) diff --git a/.pick_status.json b/.pick_status.json index 5807233d9f3..5b2590ec005 100644 --- a/.pick_status.json +++ b/.pick_status.json @@ -274,7 +274,7 @@ "description": "util: Keep quiet NaNs quiet when converting to half float.", "nominated": true, "nomination_type": 0, - "resolution": 0, + "resolution": 1, "main_sha": null, "because_sha": null }, diff --git a/src/util/half_float.c b/src/util/half_float.c index 05aeac14abb..606e4b9522e 100644 --- a/src/util/half_float.c +++ b/src/util/half_float.c @@ -83,8 +83,12 @@ _mesa_float_to_half_slow(float val) e = 31; } else if ((flt_e == 0xff) && (flt_m != 0)) { - /* NaN */ - m = 1; + /* Retain the top bits of a NaN to make sure that the quiet/signaling + * status stays the same. + */ + m = flt_m >> 13; + if (!m) + m = 1; e = 31; } else { diff --git a/src/util/softfloat.c b/src/util/softfloat.c index cc386aa46fb..2ff835f7452 100644 --- a/src/util/softfloat.c +++ b/src/util/softfloat.c @@ -1452,7 +1452,12 @@ _mesa_float_to_half_rtz_slow(float val) if (flt_m != 0) { /* 'val' is a NaN, return NaN */ e = 0x1f; - m = 0x1; + /* Retain the top bits of a NaN to make sure that the quiet/signaling + * status stays the same. + */ + m = flt_m >> 13; + if (!m) + m = 1; return (s << 15) + (e << 10) + m; }