diff -r 56cd8111b7f7 -r 41300fa6a67c src/corelib/global/qmalloc.cpp --- a/src/corelib/global/qmalloc.cpp Tue Jan 26 12:42:25 2010 +0200 +++ b/src/corelib/global/qmalloc.cpp Tue Feb 02 00:43:10 2010 +0200 @@ -65,4 +65,62 @@ return ::realloc(ptr, size); } +void *qMallocAligned(size_t size, size_t alignment) +{ + return qReallocAligned(0, size, 0, alignment); +} + +void *qReallocAligned(void *oldptr, size_t newsize, size_t oldsize, size_t alignment) +{ + // fake an aligned allocation + Q_UNUSED(oldsize); + + void *actualptr = oldptr ? static_cast(oldptr)[-1] : 0; + if (alignment <= sizeof(void*)) { + // special, fast case + void **newptr = static_cast(qRealloc(actualptr, newsize + sizeof(void*))); + if (!newptr) + return 0; + if (newptr == actualptr) { + // realloc succeeded without reallocating + return oldptr; + } + + *newptr = newptr; + return newptr + 1; + } + + union { void *ptr; void **pptr; quintptr n; } real, faked; + + // qMalloc 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. + + real.ptr = qRealloc(actualptr, newsize + alignment); + if (!real.ptr) + return 0; + + faked.n = real.n + alignment; + faked.n &= ~(alignment - 1); + + // 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.pptr[-1] = real.ptr; + + return faked.ptr; +} + +void qFreeAligned(void *ptr) +{ + if (!ptr) + return; + void **ptr2 = static_cast(ptr); + free(ptr2[-1]); +} + QT_END_NAMESPACE