/*
 * This module implements a hash table class for mapping C/C++ addresses to the
 * corresponding wrapped Python object.
 *
 * Copyright (c) 2005
 * 	Riverbank Computing Limited <info@riverbankcomputing.co.uk>
 * 
 * This file is part of SIP.
 * 
 * This copy of SIP is licensed for use under the terms of the SIP License
 * Agreement.  See the file LICENSE for more details.
 * 
 * SIP is supplied WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 */


#include <string.h>

#include "sip.h"
#include "sipint.h"


#define hash_1(k,s)	(((unsigned long)(k)) % (s))
#define hash_2(k,s)	((s) - 2 - (hash_1((k),(s)) % ((s) - 2)))


/* Prime numbers to use as hash table sizes. */
static unsigned long hash_primes[] = {
	521,        1031,       2053,       4099,
	8209,       16411,      32771,      65537,      131101,     262147,
	524309,     1048583,    2097169,    4194319,    8388617,    16777259,
	33554467,   67108879,   134217757,  268435459,  536870923,  1073741827,
	2147483659U,0
};


static sipHashEntry *newHashTable(unsigned long);
static sipHashEntry *findHashEntry(sipObjectMap *,void *);
static void reorganiseMap(sipObjectMap *om);


/*
 * Initialise an object map.
 */
void sipOMInit(sipObjectMap *om)
{
	om -> primeIdx = 0;
	om -> unused = om -> size = hash_primes[om -> primeIdx];
	om -> stale = 0;
	om -> hash_array = newHashTable(om -> size);
}


/*
 * Finalise an object map.
 */
void sipOMFinalise(sipObjectMap *om)
{
	sip_api_free(om -> hash_array);
}


/*
 * Allocate and initialise a new hash table.
 */
static sipHashEntry *newHashTable(unsigned long size)
{
	size_t nbytes;
	sipHashEntry *hashtab;

	nbytes = sizeof (sipHashEntry) * size;

	if ((hashtab = (sipHashEntry *)sip_api_malloc(nbytes)) != NULL)
		memset(hashtab,0,nbytes);

	return hashtab;
}


/*
 * Return a pointer to the hash entry that is used, or should be used, for the
 * given C/C++ address.
 */
static sipHashEntry *findHashEntry(sipObjectMap *om,void *key)
{
	unsigned long hash, inc;
	void *hek;

	hash = hash_1(key,om -> size);
	inc = hash_2(key,om -> size);

	while ((hek = om -> hash_array[hash].key) != NULL && hek != key)
		hash = (hash + inc) % om -> size;

	return &om -> hash_array[hash];
}


/*
 * Return the wrapped Python object of a specific type for a C/C++ address or
 * NULL if it wasn't found.
 */
sipWrapper *sipOMFindObject(sipObjectMap *om,void *key,sipWrapperType *type)
{
	sipHashEntry *he = findHashEntry(om,key);
	sipWrapper *w;

	/* Go through each wrapped object at this address. */
	for (w = he -> first; w != NULL; w = w -> next)
	{
		/*
		 * If this wrapped object is of the given type, or a sub-type
		 * of it, or vice versa, then we assume it is the same C++
		 * object.
		 */
#if PY_VERSION_HEX >= 0x02050000
		if (PyObject_TypeCheck(w,&type -> super.ht_type) ||
		    PyType_IsSubtype(&type -> super.ht_type,w -> ob_type))
#else
		if (PyObject_TypeCheck(w,&type -> super.type) ||
		    PyType_IsSubtype(&type -> super.type,w -> ob_type))
#endif
			return w;
	}

	return NULL;
}


/*
 * Add a C/C++ address and the corresponding wrapped Python object to the map.
 */
void sipOMAddObject(sipObjectMap *om,sipWrapper *val)
{
	sipHashEntry *he = findHashEntry(om,val -> u.cppPtr);

	/*
	 * If the bucket is in use then we appear to have several objects at
	 * the same address.
	 */
	if (he -> first != NULL)
	{
		/*
		 * This can happen for three reasons.  A variable of one class
		 * can be declared at the start of another class.  Therefore
		 * there are two objects, of different classes, with the same
		 * address.  The second reason is that the old C/C++ object has
		 * been deleted by C/C++ but we didn't get to find out for some
		 * reason, and a new C/C++ instance has been created at the
		 * same address.  The third reason is if we are in the process
		 * of deleting a Python object but the C++ object gets wrapped
		 * again because the C++ dtor called a method that has been
		 * re-implemented in Python.  The absence of the SIP_SHARE_MAP
		 * flag tells us that a new C++ instance has just been created
		 * and so we know the second reason is the correct one so we
		 * mark the old pointers as invalid and reuse the entry.
		 * Otherwise we just add this one to the existing list of
		 * objects at this address.
		 */
		if (!(val -> flags & SIP_SHARE_MAP))
		{
			sipWrapper *w;

			for (w = he -> first; w != NULL; w = w -> next)
				w -> u.cppPtr = NULL;

			he -> first = NULL;
		}

		val -> next = he -> first;
		he -> first = val;

		return;
	}

	/* See if the bucket was unused or stale. */
	if (he -> key == NULL)
	{
		he -> key = val -> u.cppPtr;
		om -> unused--;
	}
	else
		om -> stale--;

	/* Add the rest of the new value. */
	he -> first = val;
	val -> next = NULL;

	reorganiseMap(om);
}


/*
 * Reorganise a map if it is running short of space.
 */
static void reorganiseMap(sipObjectMap *om)
{
	unsigned long old_size, i;
	sipHashEntry *ohe, *old_tab;

	/* Don't bother if it still has more than 12% available. */
	if (om -> unused > om -> size >> 3)
		return;

	/*
	 * If reorganising (ie. making the stale buckets unused) using the same
	 * sized table would make 25% available then do that.  Otherwise use a
	 * bigger table (if possible).
	 */
	if (om -> unused + om -> stale < om -> size >> 2 && hash_primes[om -> primeIdx + 1] != 0)
		om -> primeIdx++;

	old_size = om -> size;
	old_tab = om -> hash_array;

	om -> unused = om -> size = hash_primes[om -> primeIdx];
	om -> stale = 0;
	om -> hash_array = newHashTable(om -> size);

	/* Transfer the entries from the old table to the new one. */
	ohe = old_tab;

	for (i = 0; i < old_size; ++i)
	{
		if (ohe -> key != NULL && ohe -> first != NULL)
		{
			*findHashEntry(om,ohe -> key) = *ohe;
			om -> unused--;
		}

		++ohe;
	}

	sip_api_free(old_tab);
}


/*
 * Remove a C/C++ object from the table.  Return 0 if it was removed
 * successfully.
 */
int sipOMRemoveObject(sipObjectMap *om,sipWrapper *val)
{
	sipHashEntry *he = findHashEntry(om,val -> u.cppPtr);
	sipWrapper **wp;

	for (wp = &he -> first; *wp != NULL; wp = &(*wp) -> next)
		if (*wp == val)
		{
			*wp = val -> next;

			/*
			 * If the bucket is now empty then count it as stale.
			 * Note that we do not NULL the key and count it as
			 * unused because that might throw out the search for
			 * another entry that wanted to go here, found it
			 * already occupied, and was put somewhere else.  In
			 * other words, searches must be repeatable until we
			 * reorganise the table.
			 */
			if (he -> first == NULL)
				om -> stale++;

			return 0;
		}

	return -1;
}
