Fix overflow/underflow in gfx geometry once and for all

ui/gfx/geometry/rect_unittest.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <limits>
 
 #include <stddef.h>
 
 #include "base/macros.h"
 #include "build/build_config.h"
@@ skipping 889 matching lines @@
       0.0f, f.ManhattanInternalDistance(gfx::RectF(-1.0f, 0.0f, 1.1f, 1.0f)));
   EXPECT_FLOAT_EQ(
       0.1f + kEpsilon,
       f.ManhattanInternalDistance(gfx::RectF(-1.5f, 0.0f, 1.4f, 1.0f)));
   EXPECT_FLOAT_EQ(
       kEpsilon,
       f.ManhattanInternalDistance(gfx::RectF(-1.5f, 0.0f, 1.5f, 1.0f)));
 }
 
 TEST(RectTest, IntegerOverflow) {
+  int limit = std::numeric_limits<int>::max();
+  int min_limit = std::numeric_limits<int>::min();
   int expected = 10;
-  int large_number = std::numeric_limits<int>::max() - expected;
+  int large_number = limit - expected;
 
   Rect height_overflow(0, large_number, 100, 100);
   EXPECT_EQ(large_number, height_overflow.y());
   EXPECT_EQ(expected, height_overflow.height());
 
   Rect width_overflow(large_number, 0, 100, 100);
   EXPECT_EQ(large_number, width_overflow.x());
   EXPECT_EQ(expected, width_overflow.width());
 
   Rect size_height_overflow(Point(0, large_number), Size(100, 100));
@@ skipping 38 matching lines @@
   EXPECT_EQ(Size(5, 5), set_size_overflow.size());
   set_size_overflow.set_size(size);
   EXPECT_EQ(large_offset, set_size_overflow.origin());
   EXPECT_EQ(expected_size, set_size_overflow.size());
 
   Rect set_rect_overflow;
   set_rect_overflow.SetRect(large_number, large_number, 100, 100);
   EXPECT_EQ(large_offset, set_rect_overflow.origin());
   EXPECT_EQ(expected_size, set_rect_overflow.size());
 
+  // Insetting an empty rect, but these numbers can overflow.
   Rect inset_overflow;
   inset_overflow.Inset(large_number, large_number, 100, 100);
   EXPECT_EQ(large_offset, inset_overflow.origin());
-  EXPECT_EQ(expected_size, inset_overflow.size());
+  EXPECT_EQ(gfx::Size(0, 0), inset_overflow.size());
 
   Rect offset_overflow(0, 0, 100, 100);
   offset_overflow.Offset(large_number, large_number);
   EXPECT_EQ(large_offset, offset_overflow.origin());
   EXPECT_EQ(expected_size, offset_overflow.size());
 
   Rect operator_overflow(0, 0, 100, 100);
   operator_overflow += Vector2d(large_number, large_number);
   EXPECT_EQ(large_offset, operator_overflow.origin());
   EXPECT_EQ(expected_size, operator_overflow.size());
+
+  Rect origin_maxint(limit, limit, limit, limit);
+  EXPECT_EQ(origin_maxint, Rect(gfx::Point(limit, limit), gfx::Size()));
+
+  // Expect a rect at the origin and a rect whose right/bottom is maxint
+  // create a rect that extends from 0..maxint in both extents.
+  {
+    Rect origin_small(0, 0, 100, 100);
+    Rect big_clamped(50, 50, limit, limit);
+    EXPECT_EQ(big_clamped.right(), limit);
+
+    Rect unioned = UnionRects(origin_small, big_clamped);
+    Rect rect_limit(0, 0, limit, limit);
+    EXPECT_EQ(unioned, rect_limit);
+  }
+
+  // Expect a rect that would overflow width (but not right) to be clamped
+  // and to have maxint extents after unioning.
+  {
+    Rect small(-500, -400, 100, 100);
+    Rect big(-400, -500, limit, limit);
+    // Technically, this should be limit + 100 width, but will clamp to maxint.
+    EXPECT_EQ(UnionRects(small, big), Rect(-500, -500, limit, limit));
+  }
+
+  // Expect a rect that would overflow right *and* width to be clamped.
+  {
+    Rect clamped(500, 500, limit, limit);
+    Rect positive_origin(100, 100, 500, 500);
+
+    // Ideally, this should be (100, 100, limit + 400, limit + 400).
+    // However, width overflows and would be clamped to limit, but right
+    // overflows too and so will be clamped to limit - 100.
+    Rect expected(100, 100, limit - 100, limit - 100);
+    EXPECT_EQ(UnionRects(clamped, positive_origin), expected);
+  }
+
+  // Unioning a left=minint rect with a right=maxint rect.
+  // Width is always clamped before adjusting position, so this
+  // should taking the min left/top and then finding the max width.
+  {
+    Rect left_minint(min_limit, min_limit, 1, 1);
+    Rect right_maxint(limit - 1, limit - 1, limit, limit);
+    Rect expected(min_limit, min_limit, limit, limit);
+    EXPECT_EQ(UnionRects(left_minint, right_maxint), expected);
+  }
 }
 
 }  // namespace gfx