ungoogled-chromium-xdg-aur/xproto-fix-underflow-in-Fp1616ToDouble.patch

From 5ade494a9966c7a9675af86dc42aca62fb4d806d Mon Sep 17 00:00:00 2001
From: Tom Anderson <thomasanderson@chromium.org>
Date: Wed, 21 Oct 2020 22:02:35 +0000
Subject: [PATCH] [XProto] Fix underflow in Fp1616ToDouble

x11::Input::Fp1616 should be treated as a signed integer, otherwise
-1 will underflow to 65535.  When dragging a scrollbar, this would
cause the scrollbar to snap to the bottom when the cursor is dragged
above the window's y=0 coordinate.  Verified that the issue is fixed
after this CL.

BUG=1139623,1136352
R=sky

Change-Id: Ie318006ceadde9b9ce3e267fb453ddeba0e81da0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485620
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819538}
---
 ui/events/x/events_x_utils.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ui/events/x/events_x_utils.cc b/ui/events/x/events_x_utils.cc
index 3010db5f40c..856dfb221e7 100644
--- a/ui/events/x/events_x_utils.cc
+++ b/ui/events/x/events_x_utils.cc
@@ -376,7 +376,7 @@ base::TimeTicks TimeTicksFromXEvent(const x11::Event& xev) {
 
 // This is ported from libxi's FP1616toDBL in XExtInt.c
 double Fp1616ToDouble(x11::Input::Fp1616 x) {
-  auto x32 = static_cast<uint32_t>(x);
+  auto x32 = static_cast<int32_t>(x);
   return x32 * 1.0 / (1 << 16);
 }