2 files changed, 26 insertions, 13 deletions
diff --git a/src/corelib/tools/qringbuffer.cpp b/src/corelib/tools/qringbuffer.cpp
index 85cfdaf1294..5345b442043 100644
--- a/src/corelib/tools/qringbuffer.cpp
+++ b/src/corelib/tools/qringbuffer.cpp
@@ -193,20 +193,33 @@ void QRingBuffer::clear()
     bufferSize = 0;
 }
 
-qint64 QRingBuffer::indexOf(char c, qint64 maxLength) const
+qint64 QRingBuffer::indexOf(char c, qint64 maxLength, qint64 pos) const
 {
-    qint64 index = 0;
-    qint64 j = head;
-    for (int i = 0; index < maxLength && i < buffers.size(); ++i) {
-        const char *ptr = buffers[i].constData() + j;
-        j = qMin(index + (i == tailBuffer ? tail : buffers[i].size()) - j, maxLength);
-
-        while (index < j) {
-            if (*ptr++ == c)
-                return index;
-            ++index;
+    if (maxLength <= 0 || pos < 0)
+        return -1;
+
+    qint64 index = -(pos + head);
+    for (int i = 0; i < buffers.size(); ++i) {
+        const qint64 nextBlockIndex = qMin(index + (i == tailBuffer ? tail : buffers[i].size()),
+                                           maxLength);
+
+        if (nextBlockIndex > 0) {
+            const char *ptr = buffers[i].constData();
+            if (index < 0) {
+                ptr -= index;
+                index = 0;
+            }
+
+            do {
+                if (*ptr++ == c)
+                    return index + pos;
+            } while (++index < nextBlockIndex);
+
+            if (index == maxLength)
+                return -1;
+        } else {
+            index = nextBlockIndex;
         }
-        j = 0;
     }
     return -1;
 }
diff --git a/src/corelib/tools/qringbuffer_p.h b/src/corelib/tools/qringbuffer_p.h
index 68509a6a80a..e7e80bc02ce 100644
--- a/src/corelib/tools/qringbuffer_p.h
+++ b/src/corelib/tools/qringbuffer_p.h
@@ -114,7 +114,7 @@ public:
 
     Q_CORE_EXPORT void clear();
     inline qint64 indexOf(char c) const { return indexOf(c, size()); }
-    Q_CORE_EXPORT qint64 indexOf(char c, qint64 maxLength) const;
+    Q_CORE_EXPORT qint64 indexOf(char c, qint64 maxLength, qint64 pos = 0) const;
     Q_CORE_EXPORT qint64 read(char *data, qint64 maxLength);
     Q_CORE_EXPORT QByteArray read();
     Q_CORE_EXPORT qint64 peek(char *data, qint64 maxLength, qint64 pos = 0) const;