Introduce Mem_MallocA() that is like alloca() but falls back to heap memory for bigger allocations #627
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When requesting < 1 MB, _alloca16() is used, otherwise Mem_Alloc16(). Furthermore you must pass a bool that will get true assigned if the memory has been allocated on the stack, else false. At the end of the function you must call Mem_FreeA( ptr, onStack ) (where onStack is the aforementioned bool), so Mem_Free16() can be called if it was allocated on the heap.
one step to making HD models (like https://www.moddb.com/mods/birdman-doom3/downloads/birdman-doom3-v11 ) work, but there's still other places in the code where the HD version of that model makes dhewm3 crash
I hope that should cover all relevant cases, though there are still plenty of _alloca() and _alloca16() calls left throughout the code
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loosely based on dhewm#517, with additional fallback to base.dll if the one for fs_game_base isn't found either
also changed that logic a bit so FormatMessage() is only called when actually used and while at it, fixed the build with mingw-w64 on my system (somehow an SDL header used strcmp() and that didn't work with `#define strcmp idStr::Cmp` from Str.h)
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The use of plain alloca() causes stack overflows (or assertions meant to prevent them) when models with many polys are loaded, see #528
Mem_MallocA() is a macro that that uses _alloca16() for allocations < 1MB, and otherwise uses Mem_Alloc16(). It should be used together with Mem_FreeA() to free the memory if it came from Mem_Alloc16(). A
boolvariable must be passed to Mem_MallocA() and Mem_FreeA(), it will be set to true if _alloca16() was used and false otherwise, and Mem_FreeA() uses it to do the right thing.This is kinda like Microsoft's _malloca() and _freea(), except that doesn't need the additional bool because they can do platform-specific magic to detect whether memory is on the stack.
This could use a little more testing with unusually big models.
I tested it by playing a few levels of Prometheus and Doom 2553, according to #528 (comment) they caused problems before.