Not sure I understand this

[jmsrickland]

I have the following C sub:

void VFixPi(PCON pcon)
{
  int co;
	
  for(co = coWHITE; co <= coBLACK; co++) 
  {
	int	ipiI;
	int	ipiJ;

	for(ipiI = ipiJ = 0; ipiI < pcon->argcpi[co]; ipiI++) 
	{
	  PPI ppiI = &pcon->argpi[co][ipiI];

	  if(!ppiI->fDead) 
	  {
		PPI ppiJ = &pcon->argpi[co][ipiJ++];

		*ppiJ = *ppiI;

		pcon->argsq[ppiJ->isq].ppi = ppiJ;
	  }
	}
	pcon->argcpi[co] = ipiJ;
  }
}

Note the code line *ppiJ = *ppiI;. These two always have the same address so it appears to me that the contents of the structure pointed to by ppiI is copied to the contents of the structure pointed to by ppiJ which is the same as copying the same data to the same location so I don't understand the point of doing this

[passel]

I assume you don't have any fDead flagged values.
If fDead was set, you would skip the assignment, and ipiJ wouldn't be incremented.
So, it seems the purpose is to remove dead values, compacting the array using i to index through all the fields, and copy to j which is incremented for non-dead fields.
Only when you have a dead field will i increment while j doesn't so in the end all the non-dead fields will be packed to the front of pcon->argpi[co].
If no fields are dead, then i will equal j the whole way. If you have some dead fields, i will lead j after that point.