diff options
| -rw-r--r-- | src/corelib/tools/qdatetime.cpp | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/src/corelib/tools/qdatetime.cpp b/src/corelib/tools/qdatetime.cpp index fa4ac2b00f..ff20c57166 100644 --- a/src/corelib/tools/qdatetime.cpp +++ b/src/corelib/tools/qdatetime.cpp @@ -90,14 +90,25 @@ static inline QDate fixedDate(int y, int m, int d) return result; } +/* + Until C++11, rounding direction is implementation-defined. + + For negative operands, implementations may chose to round down instead of + towards zero (truncation). We only actually care about the case a < 0, as all + uses of floordiv have b > 0. In this case, if rounding is down we have a % b + >= 0 and simple division works fine; but a % b = a - (a / b) * b always, so + rounding towards zero gives a % b <= 0; when < 0, we need to adjust. + + Once we assume C++11, we can safely test a < 0 instead of a % b < 0. + */ static inline qint64 floordiv(qint64 a, int b) { - return (a - (a < 0 ? b-1 : 0)) / b; + return (a - (a % b < 0 ? b - 1 : 0)) / b; } static inline int floordiv(int a, int b) { - return (a - (a < 0 ? b-1 : 0)) / b; + return (a - (a % b < 0 ? b - 1 : 0)) / b; } static inline qint64 julianDayFromDate(int year, int month, int day) |