compute center slightly slower to avoid overflow

Bug: oss-fuzz:8509
Change-Id: I13b1a77e1549070827a7cc534b062ec85aad255e
Reviewed-on: https://skia-review.googlesource.com/129930
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>

2 files changed, 29 insertions, 2 deletions

diff --git a/include/core/SkRect.h b/include/core/SkRect.h
index 2a46da68c6..920572f317 100644
--- a/include/core/SkRect.h
+++ b/include/core/SkRect.h
@@ -931,14 +931,20 @@ struct SK_API SkRect {
 
         @return  midpoint in x
     */
-    SkScalar    centerX() const { return SkScalarHalf(fLeft + fRight); }
+    SkScalar centerX() const {
+        // don't use SkScalarHalf(fLeft + fBottom) as that might overflow before the 0.5
+        return SkScalarHalf(fLeft) + SkScalarHalf(fRight);
+    }
 
     /** Returns average of top edge and bottom edge. Result does not change if SkRect
         is sorted. Result may overflow to infinity if SkRect is far from the origin.
 
         @return  midpoint in y
     */
-    SkScalar    centerY() const { return SkScalarHalf(fTop + fBottom); }
+    SkScalar centerY() const {
+        // don't use SkScalarHalf(fTop + fBottom) as that might overflow before the 0.5
+        return SkScalarHalf(fTop) + SkScalarHalf(fBottom);
+    }
 
     /** Returns true if all members in a: fLeft, fTop, fRight, and fBottom; are
         equal to the corresponding members in b.
diff --git a/tests/RectTest.cpp b/tests/RectTest.cpp
index 7d2601a8be..2594c53cac 100644
--- a/tests/RectTest.cpp
+++ b/tests/RectTest.cpp
@@ -139,3 +139,24 @@ DEF_TEST(Rect_setbounds, reporter) {
         }
     }
 }
+
+static float make_big_value(skiatest::Reporter* reporter) {
+    // need to make a big value, one that will cause rect.width() to overflow to inf.
+    // however, the windows compiler wants about this if it can see the big value inlined.
+    // hence, this stupid trick to try to fool their compiler.
+    SkASSERT(reporter);
+    return reporter ? SK_ScalarMax * 0.75f : 0;
+}
+
+DEF_TEST(Rect_center, reporter) {
+    // ensure we can compute center even when the width/height might overflow
+    const SkScalar big = make_big_value(reporter);
+    const SkRect r = { -big, -big, big, big };
+
+    REPORTER_ASSERT(reporter, r.isFinite());
+    REPORTER_ASSERT(reporter, SkScalarIsFinite(r.centerX()));
+    REPORTER_ASSERT(reporter, SkScalarIsFinite(r.centerY()));
+    REPORTER_ASSERT(reporter, !SkScalarIsFinite(r.width()));
+    REPORTER_ASSERT(reporter, !SkScalarIsFinite(r.height()));
+}
+