Function with constant & static local variable, makes function reentrant?

Question

I have a function with a local variable who is static & constant, does the function is reentrant?

This is the code:

void foo(unsigned char *pucBuffer,
         int            iBytes,
         unsigned int  *puiOUT)
{
   static const long rg_uliLUT[4] = {0x00000000, 0x77073096, 0xee0e612c,
                                     0x990951ba};
   while(iBytes--)
   {
     *puiOUT = (*puiOUT >> 8) ^ rg_uliLUT[(*puiOUT & 0x03) ^ *pucBuffer++];
   }
}

Thank you in advance :D

Answer 1

As long as rg_uliLUT is const then yes, I think your function is re-entrant. If that variable were not const and was modified then the answer would be no, but because it is constant, no caller will be able to modify another caller's state variables (anything that can be changed is on the caller's private stack and the only "shared" data cannot be changed).

From good old wikipedia

In computing, a computer program or subroutine is called reentrant if it can be interrupted in the middle of its execution and then safely called again ("re-entered") before its previous invocation's complete execution.

All the function state is private to each caller (on caller stack). The only other state is constant, so because the caller can't modify it, to any other caller it will always look the same, so won't change function behavior if two threads, for example, are in the function at the same time.

PS: It is not re-entrant if the memory pointed to by puiOUT is shared between callers. Also seems like pucBuffer could be char const * because it is not written to.