Thread: Help for understanding of a C code

Is it this?
http://brlcad.org/docs/doxygen-r6411...h_source.xhtml

TBH the whole thing is just a hack to try and trap memory errors in C programming.

The code will work if you assume it does nothing, which is what you get if NO_BOMBING_MACROS is defined.

What are you trying to achieve (or learn)?

If you're hoping to convert all that C code (in the entire suite) to Python, you're going to be a while doing it.

If you just want to call the code from your Python code, then do that. Python has lots of tools for wrapping up code written in other languages and making it callable from Python.

Anyhooooo

Code:

if (UNLIKELY(
    (_ptrval == 0) || 
    (_ptrval & (sizeof(_ptrval) - 1)) ||
    *((const uint32_t *) (_ptr)) != (uint32_t) (_magic)))
{
    bu_badmagic((const uint32_t *) (_ptr), (uint32_t) _magic, _str, __FILE__,  __LINE__);

1. A GCC macro that tells the compiler that the following condition is normally expected to evaluate to false, and should generate code based on this assumption.
2. Check whether ptrval is zero
3. Check whether ptrval has a bit-pattern of say xx01, xx02 or xx03.
Say sizeof(ptrval) is 4, then (sizeof(_ptrval) - 1) is 3 (aka 0x03, aka 0b00000011).
A ptrval of 4 would be fine, whereas 5 would be bad (because 5 & 3 is 1).
4. Check that the long stored at the dereferenced ptr isn't the magic value.

If any of those three predicates evaluates to true (indicating something is wrong), then crash-and-burn by calling bu_badmagic
bu_badmagic is given the __FILE__ and __LINE__ to tell the developer where the problem was identified.

Is below can be written without paranthesis ? Why do we need ()

Code:

const  uintptr_t  _ptrval = (constuintptr_t) (_ptr);