68 void *qMallocAligned(size_t size, size_t alignment)

    69 {

    70     return qReallocAligned(0, size, 0, alignment);

    71 }

    72 

    73 void *qReallocAligned(void *oldptr, size_t newsize, size_t oldsize, size_t alignment)

    74 {

    75     // fake an aligned allocation

    76     Q_UNUSED(oldsize);

    77 

    78     void *actualptr = oldptr ? static_cast<void **>(oldptr)[-1] : 0;

    79     if (alignment <= sizeof(void*)) {

    80         // special, fast case

    81         void **newptr = static_cast<void **>(qRealloc(actualptr, newsize + sizeof(void*)));

    82         if (!newptr)

    83             return 0;

    84         if (newptr == actualptr) {

    85             // realloc succeeded without reallocating

    86             return oldptr;

    87         }

    88 

    89         *newptr = newptr;

    90         return newptr + 1;

    91     }

    92 

    93     union { void *ptr; void **pptr; quintptr n; } real, faked;

    94 

    95     // qMalloc returns pointers aligned at least at sizeof(size_t) boundaries

    96     // but usually more (8- or 16-byte boundaries).

    97     // So we overallocate by alignment-sizeof(size_t) bytes, so we're guaranteed to find a

    98     // somewhere within the first alignment-sizeof(size_t) that is properly aligned.

    99 

   100     // However, we need to store the actual pointer, so we need to allocate actually size +

   101     // alignment anyway.

   102 

   103     real.ptr = qRealloc(actualptr, newsize + alignment);

   104     if (!real.ptr)

   105         return 0;

   106 

   107     faked.n = real.n + alignment;

   108     faked.n &= ~(alignment - 1);

   109 

   110     // now save the value of the real pointer at faked-sizeof(void*)

   111     // by construction, alignment > sizeof(void*) and is a power of 2, so

   112     // faked-sizeof(void*) is properly aligned for a pointer

   113     faked.pptr[-1] = real.ptr;

   114 

   115     return faked.ptr;

   116 }

   117 

   118 void qFreeAligned(void *ptr)

   119 {

   120     if (!ptr)

   121         return;

   122     void **ptr2 = static_cast<void **>(ptr);

   123     free(ptr2[-1]);

   124 }

   125