Remove needless loop in QIODevice::seek

Either the buffer has more data than is being skipped and it can be
cleared or it doesn't and we must skip it.

If the total size of QRingBuffer exceeds INT_MAX there'll be bigger
problems (e.g., QRingBuffer::size() will overflow) that can only be
handled there and there's no point trying to work around them here.

Reviewed-by: Markus Goetz

1 files changed, 7 insertions, 12 deletions

diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index 4494d2ad07..856d737796 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -619,7 +619,8 @@ qint64 QIODevice::size() const
 */
 bool QIODevice::seek(qint64 pos)
 {
-    if (d_func()->openMode == NotOpen) {
+    Q_D(QIODevice);
+    if (d->openMode == NotOpen) {
         qWarning("QIODevice::seek: The device is not open");
         return false;
     }
@@ -628,7 +629,6 @@ bool QIODevice::seek(qint64 pos)
         return false;
     }
 
-    Q_D(QIODevice);
 #if defined QIODEVICE_DEBUG
     printf("%p QIODevice::seek(%d), before: d->pos = %d, d->buffer.size() = %d\n",
            this, int(pos), int(d->pos), d->buffer.size());
@@ -640,21 +640,16 @@ bool QIODevice::seek(qint64 pos)
         d->devicePos = pos;
     }
 
-    if (offset > 0 && !d->buffer.isEmpty()) {
-        // When seeking forwards, we need to pop bytes off the front of the
-        // buffer.
-        do {
-            int bytesToSkip = int(qMin<qint64>(offset, INT_MAX));
-            d->buffer.skip(bytesToSkip);
-            offset -= bytesToSkip;
-        } while (offset > 0);
-    } else if (offset < 0) {
+    if (offset < 0
+            || offset >= qint64(d->buffer.size()))
         // When seeking backwards, an operation that is only allowed for
         // random-access devices, the buffer is cleared. The next read
         // operation will then refill the buffer. We can optimize this, if we
         // find that seeking backwards becomes a significant performance hit.
         d->buffer.clear();
-    }
+    else if (!d->buffer.isEmpty())
+        d->buffer.skip(int(offset));
+
 #if defined QIODEVICE_DEBUG
     printf("%p \tafter: d->pos == %d, d->buffer.size() == %d\n", this, int(d->pos),
            d->buffer.size());