Large old program systems developing for tens of years contain a lot of various atavisms and code sections which have been simply written with the use of popular paradigms and styles of different ages. You can watch evolution of programming languages - the oldest code sections are written in C and the most recent contain complex templates in Alexandrescu style.

There are atavisms relating to 64-bit mode as well. To be more exact, they are atavisms which prevent modern 64-bit code from correct operation. I will give you two examples I have learned recently.

The interesting error relates to an old version of Mac OS X system and is situated inside the function malloc_zone_calloc:

// beyond this, assume a programming error #define MAX_ALLOCATION 0xc0000000 // Allocate cleared (zero-filled) memory from // the given zone for num_items objects, // each of which is size bytes large void *malloc_zone_calloc(malloc_zone_t *zone, size_t num_items, size_t size) { void *ptr; if (malloc_check_start && (malloc_check_counter++ >= malloc_check_start)) { internal_check(); } if (((unsigned)num_items >= MAX_ALLOCATION) || ((unsigned)size >= MAX_ALLOCATION) || ((long long)size * num_items >= (long long) MAX_ALLOCATION)) { /* Probably a programming error */ fprintf(stderr, "*** malloc_zone_calloc[%d]: arguments too large: %d,%d

", getpid(), (unsigned)num_items, (unsigned)size); return NULL; } ptr = zone->calloc(zone, num_items, size); if (malloc_logger) malloc_logger(MALLOC_LOG_TYPE_ALLOCATE | MALLOC_LOG_TYPE_HAS_ZONE | MALLOC_LOG_TYPE_CLEARED, (unsigned)zone, num_items * size, 0, (unsigned)ptr, 0); return ptr; }

Firstly, the function's code contains check of the sizes of memory being allocated strange for the 64-bit system. And secondly, the diagnostic warning you see is incorrect for if we ask to allocate memory for 4 400 000 000 items, due to explicit conversion of the type to unsigned, we will see a strange diagnostic warning about impossibility to allocate memory only for 105 032 704 items.

As far as I understood the note, this strange check was removed from the function only in 2006. Although I may be wrong about the date of correction, this example shows rather well how easy it is to forget about something old.