Unify all mid() functions in QtBase.

Up to now, Qt had at least 3 different implementations of the mid().
Only QString::mid implementation was not crashing on edge cases and
was protected against overflows, therefore I picked that one as the
base implementation, even if it has weird semantics for an invalid
input.

As a side effect QVector::mid was slightly optimized to not detach in
all cases (which follows current QList behavior). Documentation of
QVector::mid and QList::mid was updated to not mention "copy of data"
which could suggest that the mid() result is detached.

QStringRef::mid was fixed and now it follows general Qt behavior, by
returning a null value for a null input.

Change-Id: Ie9ff5d98372bd193d66508e6dd92b6ed1180ad9b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index 2d744f97c0..4047bf611f 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -130,4 +130,33 @@ void QArrayData::deallocate(QArrayData *data, size_t objectSize,
     ::free(data);
 }
 
+namespace QtPrivate {
+/*!
+  \internal
+*/
+QContainerImplHelper::CutResult QContainerImplHelper::mid(int originalLength, int *_position, int *_length)
+{
+    int &position = *_position;
+    int &length = *_length;
+    if (position > originalLength)
+        return Null;
+
+    if (position < 0) {
+        if (length < 0 || length + position >= originalLength)
+            return Full;
+        if (length + position <= 0)
+            return Null;
+        length += position;
+        position = 0;
+    } else if (uint(length) > uint(originalLength - position)) {
+        length = originalLength - position;
+    }
+
+    if (position == 0 && length == originalLength)
+        return Full;
+
+    return length > 0 ? Subset : Empty;
+}
+}
+
 QT_END_NAMESPACE