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// Copyright (C) 2020 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
#include "qplatformdefs.h"
#include <stdlib.h>
#include <string.h>
/*
Define the container allocation functions in a separate file, so that our
users can easily override them.
*/
QT_BEGIN_NAMESPACE
void *qMallocAligned(size_t size, size_t alignment)
{
return qReallocAligned(nullptr, size, 0, alignment);
}
void *qReallocAligned(void *oldptr, size_t newsize, size_t oldsize, size_t alignment)
{
// fake an aligned allocation
void *actualptr = oldptr ? static_cast<void **>(oldptr)[-1] : nullptr;
if (alignment <= sizeof(void *)) {
// special, fast case
void **newptr = static_cast<void **>(realloc(actualptr, newsize + sizeof(void *)));
if (!newptr)
return nullptr;
if (newptr == actualptr) {
// realloc succeeded without reallocating
return oldptr;
}
*newptr = newptr;
return newptr + 1;
}
// malloc returns pointers aligned at least at sizeof(size_t) boundaries
// but usually more (8- or 16-byte boundaries).
// So we overallocate by alignment-sizeof(size_t) bytes, so we're guaranteed to find a
// somewhere within the first alignment-sizeof(size_t) that is properly aligned.
// However, we need to store the actual pointer, so we need to allocate actually size +
// alignment anyway.
qptrdiff oldoffset = oldptr ? static_cast<char *>(oldptr) - static_cast<char *>(actualptr) : 0;
void *real = realloc(actualptr, newsize + alignment);
if (!real)
return nullptr;
quintptr faked = reinterpret_cast<quintptr>(real) + alignment;
faked &= ~(alignment - 1);
void **faked_ptr = reinterpret_cast<void **>(faked);
if (oldptr) {
qptrdiff newoffset = reinterpret_cast<char *>(faked_ptr) - static_cast<char *>(real);
if (oldoffset != newoffset)
memmove(faked_ptr, static_cast<char *>(real) + oldoffset, qMin(oldsize, newsize));
}
// now save the value of the real pointer at faked-sizeof(void*)
// by construction, alignment > sizeof(void*) and is a power of 2, so
// faked-sizeof(void*) is properly aligned for a pointer
faked_ptr[-1] = real;
return faked_ptr;
}
void qFreeAligned(void *ptr)
{
if (!ptr)
return;
void **ptr2 = static_cast<void **>(ptr);
free(ptr2[-1]);
}
QT_END_NAMESPACE
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