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39
40#include "qplatformdefs.h"
41
42#include <stdlib.h>
43#include <string.h>
44
45/*
46 Define the container allocation functions in a separate file, so that our
47 users can easily override them.
48*/
49
50QT_BEGIN_NAMESPACE
51
52void *qMallocAligned(size_t size, size_t alignment)
53{
54 return qReallocAligned(nullptr, size, 0, alignment);
55}
56
57void *qReallocAligned(void *oldptr, size_t newsize, size_t oldsize, size_t alignment)
58{
59 // fake an aligned allocation
60 void *actualptr = oldptr ? static_cast<void **>(oldptr)[-1] : nullptr;
61 if (alignment <= sizeof(void *)) {
62 // special, fast case
63 void **newptr = static_cast<void **>(realloc(actualptr, newsize + sizeof(void *)));
64 if (!newptr)
65 return nullptr;
66 if (newptr == actualptr) {
67 // realloc succeeded without reallocating
68 return oldptr;
69 }
70
71 *newptr = newptr;
72 return newptr + 1;
73 }
74
75 // malloc returns pointers aligned at least at sizeof(size_t) boundaries
76 // but usually more (8- or 16-byte boundaries).
77 // So we overallocate by alignment-sizeof(size_t) bytes, so we're guaranteed to find a
78 // somewhere within the first alignment-sizeof(size_t) that is properly aligned.
79
80 // However, we need to store the actual pointer, so we need to allocate actually size +
81 // alignment anyway.
82
83 void *real = realloc(actualptr, newsize + alignment);
84 if (!real)
85 return nullptr;
86
87 quintptr faked = reinterpret_cast<quintptr>(real) + alignment;
88 faked &= ~(alignment - 1);
89 void **faked_ptr = reinterpret_cast<void **>(faked);
90
91 if (oldptr) {
92 qptrdiff oldoffset = static_cast<char *>(oldptr) - static_cast<char *>(actualptr);
93 qptrdiff newoffset = reinterpret_cast<char *>(faked_ptr) - static_cast<char *>(real);
94 if (oldoffset != newoffset)
95 memmove(faked_ptr, static_cast<char *>(real) + oldoffset, qMin(oldsize, newsize));
96 }
97
98 // now save the value of the real pointer at faked-sizeof(void*)
99 // by construction, alignment > sizeof(void*) and is a power of 2, so
100 // faked-sizeof(void*) is properly aligned for a pointer
101 faked_ptr[-1] = real;
102
103 return faked_ptr;
104}
105
106void qFreeAligned(void *ptr)
107{
108 if (!ptr)
109 return;
110 void **ptr2 = static_cast<void **>(ptr);
111 free(ptr2[-1]);
112}
113
114QT_END_NAMESPACE
115