From e4c6d73f925671a9c96558293472ed213861239c Mon Sep 17 00:00:00 2001 From: Marc Mutz Date: Mon, 14 Mar 2016 15:18:11 +0100 Subject: QRect: fix UB (int overflow) in center() QRect::center() should be defined for any QRect(x1,y1,x2,x2), INT_MIN <= x1, x2, y1, y2 <= INT_MAX because the average of two signed integers is always representable as a signed integer. But not when it's calculated as (x1+x2)/2, since that expression overflows when x1 > INT_MAX - x2. Instead of playing games with Hacker's Delight-style expressions, or use Google's patented algorithm, which requires two divisions, take advantage of the fact that int is not intmax_t and perform the calculation in the qint64 domain. The cast back to int is always well- defined since, as mentioned, the result is always representable in an int. Fix a test-case that expected a nonsensical result due to overflow. [ChangeLog][QtCore][QRect] Fixed integer overflow in center(). This fixes the result for some corner-cases like a 1x1 rectangle at (INT_MIN, INT_MIN), for which the previous implementation could return anything (due to invoking undefined behavior), but commonly returned (0, 0). Change-Id: I1a885ca6dff770327dd31655c3eb473fcfeb8878 Reviewed-by: Lars Knoll --- src/corelib/tools/qrect.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'src/corelib/tools/qrect.h') diff --git a/src/corelib/tools/qrect.h b/src/corelib/tools/qrect.h index 59cecf9a01..a0449ae134 100644 --- a/src/corelib/tools/qrect.h +++ b/src/corelib/tools/qrect.h @@ -245,7 +245,7 @@ Q_DECL_CONSTEXPR inline QPoint QRect::bottomLeft() const Q_DECL_NOTHROW { return QPoint(x1, y2); } Q_DECL_CONSTEXPR inline QPoint QRect::center() const Q_DECL_NOTHROW -{ return QPoint((x1+x2)/2, (y1+y2)/2); } +{ return QPoint(int((qint64(x1)+x2)/2), int((qint64(y1)+y2)/2)); } // cast avoids overflow on addition Q_DECL_CONSTEXPR inline int QRect::width() const Q_DECL_NOTHROW { return x2 - x1 + 1; } -- cgit v1.2.3