Move container block-size calculations to qarraydata.cpp

These were in qbytearray.cpp, which doesn't use them, is big and I
intend to move it to a different directory than the header,
qtools_p.h, that declares them. So move them to a small file that does
use them.

Change-Id: I5a4684f8c7628e617546019cc3f01d92d829f085
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
 
 
 
 
 

1 files changed, 104 insertions, 1 deletions

diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index bcc0688a91..88d8b8244d 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Copyright (C) 2016 Intel Corporation.
 ** Contact: https://www.qt.io/licensing/
 **
@@ -41,11 +41,114 @@
 #include <QtCore/qarraydata.h>
 #include <QtCore/private/qnumeric_p.h>
 #include <QtCore/private/qtools_p.h>
+#include <QtCore/qmath.h>
 
 #include <stdlib.h>
 
 QT_BEGIN_NAMESPACE
 
+/*
+ * This pair of functions is declared in qtools_p.h and is used by the Qt
+ * containers to allocate memory and grow the memory block during append
+ * operations.
+ *
+ * They take size_t parameters and return size_t so they will change sizes
+ * according to the pointer width. However, knowing Qt containers store the
+ * container size and element indexes in ints, these functions never return a
+ * size larger than INT_MAX. This is done by casting the element count and
+ * memory block size to int in several comparisons: the check for negative is
+ * very fast on most platforms as the code only needs to check the sign bit.
+ *
+ * These functions return SIZE_MAX on overflow, which can be passed to malloc()
+ * and will surely cause a NULL return (there's no way you can allocate a
+ * memory block the size of your entire VM space).
+ */
+
+/*!
+    \internal
+    \since 5.7
+
+    Returns the memory block size for a container containing \a elementCount
+    elements, each of \a elementSize bytes, plus a header of \a headerSize
+    bytes. That is, this function returns \c
+      {elementCount * elementSize + headerSize}
+
+    but unlike the simple calculation, it checks for overflows during the
+    multiplication and the addition.
+
+    Both \a elementCount and \a headerSize can be zero, but \a elementSize
+    cannot.
+
+    This function returns SIZE_MAX (~0) on overflow or if the memory block size
+    would not fit an int.
+*/
+size_t qCalculateBlockSize(size_t elementCount, size_t elementSize, size_t headerSize) noexcept
+{
+    unsigned count = unsigned(elementCount);
+    unsigned size = unsigned(elementSize);
+    unsigned header = unsigned(headerSize);
+    Q_ASSERT(elementSize);
+    Q_ASSERT(size == elementSize);
+    Q_ASSERT(header == headerSize);
+
+    if (Q_UNLIKELY(count != elementCount))
+        return std::numeric_limits<size_t>::max();
+
+    unsigned bytes;
+    if (Q_UNLIKELY(mul_overflow(size, count, &bytes)) ||
+            Q_UNLIKELY(add_overflow(bytes, header, &bytes)))
+        return std::numeric_limits<size_t>::max();
+    if (Q_UNLIKELY(int(bytes) < 0))     // catches bytes >= 2GB
+        return std::numeric_limits<size_t>::max();
+
+    return bytes;
+}
+
+/*!
+    \internal
+    \since 5.7
+
+    Returns the memory block size and the number of elements that will fit in
+    that block for a container containing \a elementCount elements, each of \a
+    elementSize bytes, plus a header of \a headerSize bytes. This function
+    assumes the container will grow and pre-allocates a growth factor.
+
+    Both \a elementCount and \a headerSize can be zero, but \a elementSize
+    cannot.
+
+    This function returns SIZE_MAX (~0) on overflow or if the memory block size
+    would not fit an int.
+
+    \note The memory block may contain up to \a elementSize - 1 bytes more than
+    needed.
+*/
+CalculateGrowingBlockSizeResult
+qCalculateGrowingBlockSize(size_t elementCount, size_t elementSize, size_t headerSize) noexcept
+{
+    CalculateGrowingBlockSizeResult result = {
+        std::numeric_limits<size_t>::max(),std::numeric_limits<size_t>::max()
+    };
+
+    unsigned bytes = unsigned(qCalculateBlockSize(elementCount, elementSize, headerSize));
+    if (int(bytes) < 0)     // catches std::numeric_limits<size_t>::max()
+        return result;
+
+    unsigned morebytes = qNextPowerOfTwo(bytes);
+    if (Q_UNLIKELY(int(morebytes) < 0)) {
+        // catches morebytes == 2GB
+        // grow by half the difference between bytes and morebytes
+        bytes += (morebytes - bytes) / 2;
+    } else {
+        bytes = morebytes;
+    }
+
+    result.elementCount = (bytes - unsigned(headerSize)) / unsigned(elementSize);
+    result.size = bytes;
+    return result;
+}
+
+// End of qtools_p.h implementation
+
 QT_WARNING_PUSH
 QT_WARNING_DISABLE_GCC("-Wmissing-field-initializers")