2 files changed, 38 insertions, 30 deletions

diff --git a/src/corelib/tools/qbytearray.cpp b/src/corelib/tools/qbytearray.cpp
index 90069b112d..559ba193d1 100644
--- a/src/corelib/tools/qbytearray.cpp
+++ b/src/corelib/tools/qbytearray.cpp
@@ -69,24 +69,25 @@ int qFindByteArray(
 
 int qAllocMore(int alloc, int extra)
 {
-    if (alloc == 0 && extra == 0)
-        return 0;
-    const int page = 1 << 12;
-    int nalloc;
-    alloc += extra;
-    if (alloc < 1<<6) {
-        nalloc = (1<<3) + ((alloc >>3) << 3);
-    } else  {
-        // don't do anything if the loop will overflow signed int.
-        if (alloc >= INT_MAX/2)
-            return INT_MAX;
-        nalloc = (alloc < page) ? 1 << 3 : page;
-        while (nalloc < alloc) {
-            if (nalloc <= 0)
-                return INT_MAX;
-            nalloc *= 2;
-        }
-    }
+    Q_ASSERT(alloc >= 0 && extra >= 0);
+    Q_ASSERT(alloc < (1 << 30) - extra);
+
+    unsigned nalloc = alloc + extra;
+
+    // Round up to next power of 2
+
+    // Assuming container is growing, always overshoot
+    //--nalloc;
+
+    nalloc |= nalloc >> 1;
+    nalloc |= nalloc >> 2;
+    nalloc |= nalloc >> 4;
+    nalloc |= nalloc >> 8;
+    nalloc |= nalloc >> 16;
+    ++nalloc;
+
+    Q_ASSERT(nalloc > unsigned(alloc + extra));
+
     return nalloc - extra;
 }
 
diff --git a/tests/auto/corelib/tools/qbytearray/tst_qbytearray.cpp b/tests/auto/corelib/tools/qbytearray/tst_qbytearray.cpp
index 585d6afa44..4fb74a2af5 100644
--- a/tests/auto/corelib/tools/qbytearray/tst_qbytearray.cpp
+++ b/tests/auto/corelib/tools/qbytearray/tst_qbytearray.cpp
@@ -1075,18 +1075,25 @@ void tst_QByteArray::toULongLong()
 // global function defined in qbytearray.cpp
 void tst_QByteArray::qAllocMore()
 {
-    static const int t[] = {
-        INT_MIN, INT_MIN + 1, -1234567, -66000, -1025,
-        -3, -1, 0, +1, +3, +1025, +66000, +1234567, INT_MAX - 1, INT_MAX,
-        INT_MAX/3
-    };
-    static const int N = sizeof(t)/sizeof(t[0]);
-
-    // make sure qAllocMore() doesn't loop infinitely on any input
-    for (int i = 0; i < N; ++i) {
-        for (int j = 0; j < N; ++j) {
-            ::qAllocMore(t[i], t[j]);
-        }
+    using QT_PREPEND_NAMESPACE(qAllocMore);
+
+    // Not very important, but please behave :-)
+    QVERIFY(qAllocMore(0, 0) >= 0);
+
+    for (int i = 1; i < 1 << 8; i <<= 1)
+        QVERIFY(qAllocMore(i, 0) >= i);
+
+    for (int i = 1 << 8; i < 1 << 30; i <<= 1) {
+        const int alloc = qAllocMore(i, 0);
+
+        QVERIFY(alloc >= i);
+        QCOMPARE(qAllocMore(i - 8, 8), alloc - 8);
+        QCOMPARE(qAllocMore(i - 16, 16), alloc - 16);
+        QCOMPARE(qAllocMore(i - 24, 24), alloc - 24);
+        QCOMPARE(qAllocMore(i - 32, 32), alloc - 32);
+
+        QVERIFY(qAllocMore(i - 1, 0) >= i - 1);
+        QVERIFY(qAllocMore(i + 1, 0) >= i + 1);
     }
 }