OpenFPGA/vpr7_x2p/vpr/SRC/pack/prepack.c

/* 
 Prepacking: Group together technology-mapped netlist blocks before packing.  This gives hints to the packer on what groups of blocks to keep together during packing.
 Primary purpose 1) "Forced" packs (eg LUT+FF pair)
 2) Carry-chains


 Duties: Find pack patterns in architecture, find pack patterns in netlist.

 Author: Jason Luu
 March 12, 2012
 */
#include <stdio.h>
#include <assert.h>
#include <string.h>

#include "read_xml_arch_file.h"
#include "util.h"
#include "vpr_types.h"
#include "globals.h"
#include "hash.h"
#include "prepack.h"
#include "vpr_utils.h"
#include "ReadOptions.h"

/*****************************************/
/*Local Function Declaration			 */
/*****************************************/
static int add_pattern_name_to_hash(INOUTP struct s_hash **nhash,
		INP char *pattern_name, INOUTP int *ncount);
static void discover_pattern_names_in_pb_graph_node(
		INOUTP t_pb_graph_node *pb_graph_node, INOUTP struct s_hash **nhash,
		INOUTP int *ncount);
static void forward_infer_pattern(INOUTP t_pb_graph_pin *pb_graph_pin);
static void backward_infer_pattern(INOUTP t_pb_graph_pin *pb_graph_pin);
static t_pack_patterns *alloc_and_init_pattern_list_from_hash(INP int ncount,
		INOUTP struct s_hash **nhash);
static t_pb_graph_edge * find_expansion_edge_of_pattern(INP int pattern_index,
		INP t_pb_graph_node *pb_graph_node);
static void forward_expand_pack_pattern_from_edge(
		INP t_pb_graph_edge *expansion_edge,
		INOUTP t_pack_patterns *list_of_packing_patterns,
		INP int curr_pattern_index, INP int *L_num_blocks, INP boolean make_root_of_chain);
static void backward_expand_pack_pattern_from_edge(
		INP t_pb_graph_edge* expansion_edge,
		INOUTP t_pack_patterns *list_of_packing_patterns,
		INP int curr_pattern_index, INP t_pb_graph_pin *destination_pin,
		INP t_pack_pattern_block *destination_block, INP int *L_num_blocks);
static int compare_pack_pattern(const t_pack_patterns *pattern_a, const t_pack_patterns *pattern_b);
static void free_pack_pattern(INOUTP t_pack_pattern_block *pattern_block, INOUTP t_pack_pattern_block **pattern_block_list);
static t_pack_molecule *try_create_molecule(
		INP t_pack_patterns *list_of_pack_patterns, INP int pack_pattern_index,
		INP int block_index);
static boolean try_expand_molecule(INOUTP t_pack_molecule *molecule,
		INP int logical_block_index,
		INP t_pack_pattern_block *current_pattern_block);
static void print_pack_molecules(INP const char *fname,
		INP t_pack_patterns *list_of_pack_patterns, INP int num_pack_patterns,
		INP t_pack_molecule *list_of_molecules);
static t_pb_graph_node *get_expected_lowest_cost_primitive_for_logical_block(INP int ilogical_block);
static t_pb_graph_node *get_expected_lowest_cost_primitive_for_logical_block_in_pb_graph_node(INP int ilogical_block, INP t_pb_graph_node *curr_pb_graph_node, OUTP float *cost);
static int find_new_root_atom_for_chain(INP int block_index, INP t_pack_patterns *list_of_pack_pattern);

/*****************************************/
/*Function Definitions					 */
/*****************************************/

/**
 * Find all packing patterns in architecture 
 * [0..num_packing_patterns-1]
 *
 * Limitations: Currently assumes that forced pack nets must be single-fanout as this covers all the reasonable architectures we wanted.
 More complicated structures should probably be handled either downstream (general packing) or upstream (in tech mapping)
 *              If this limitation is too constraining, code is designed so that this limitation can be removed
 */
t_pack_patterns *alloc_and_load_pack_patterns(OUTP int *num_packing_patterns) {
	int i, j, ncount, k;
	int L_num_blocks;
	struct s_hash **nhash;
	t_pack_patterns *list_of_packing_patterns;
	t_pb_graph_edge *expansion_edge;

	/* alloc and initialize array of packing patterns based on architecture complex blocks */
	nhash = alloc_hash_table();
	ncount = 0;
	for (i = 0; i < num_types; i++) {
		discover_pattern_names_in_pb_graph_node(type_descriptors[i].pb_graph_head, nhash, &ncount);
	}

	list_of_packing_patterns = alloc_and_init_pattern_list_from_hash(ncount,
			nhash);

	/* load packing patterns by traversing the edges to find edges belonging to pattern */
	for (i = 0; i < ncount; i++) {
		for (j = 0; j < num_types; j++) {
			expansion_edge = find_expansion_edge_of_pattern(i, type_descriptors[j].pb_graph_head);
			if (expansion_edge == NULL) {
				continue;
			}
			L_num_blocks = 0;
			list_of_packing_patterns[i].base_cost = 0;
			backward_expand_pack_pattern_from_edge(expansion_edge, list_of_packing_patterns, i, NULL, NULL, &L_num_blocks);
			list_of_packing_patterns[i].num_blocks = L_num_blocks;

			/* Default settings: A section of a netlist must match all blocks in a pack pattern before it can be made a molecule except for carry-chains.  For carry-chains, since carry-chains are typically
			quite flexible in terms of size, it is optional whether or not an atom in a netlist matches any particular block inside the chain */
			list_of_packing_patterns[i].is_block_optional = (boolean*) my_malloc(L_num_blocks * sizeof(boolean));
			for(k = 0; k < L_num_blocks; k++) {
				list_of_packing_patterns[i].is_block_optional[k] = FALSE;
				if(list_of_packing_patterns[i].is_chain && list_of_packing_patterns[i].root_block->block_id != k) {
					list_of_packing_patterns[i].is_block_optional[k] = TRUE;
				}
			}
			break;
		}
	}

	free_hash_table(nhash);

	*num_packing_patterns = ncount;

	return list_of_packing_patterns;
}

/**
 * Adds pack pattern name to hashtable of pack pattern names.
 */
static int add_pattern_name_to_hash(INOUTP struct s_hash **nhash,
		INP char *pattern_name, INOUTP int *ncount) {
	struct s_hash *hash_value;

	hash_value = insert_in_hash_table(nhash, pattern_name, *ncount);
	if (hash_value->count == 1) {
		assert(*ncount == hash_value->index);
		(*ncount)++;
	}
	return hash_value->index;
}

/**
 * Locate all pattern names 
 * Side-effect: set all pb_graph_node temp_scratch_pad field to NULL
 *				For cases where a pattern inference is "obvious", mark it as obvious.
 */
static void discover_pattern_names_in_pb_graph_node(
		INOUTP t_pb_graph_node *pb_graph_node, INOUTP struct s_hash **nhash,
		INOUTP int *ncount) {
	int i, j, k, m;
	int index;
	boolean hasPattern;
	/* Iterate over all edges to discover if an edge in current physical block belongs to a pattern 
	 If edge does, then record the name of the pattern in a hash table
	 */

	if (pb_graph_node == NULL) {
		return;
	}

	pb_graph_node->temp_scratch_pad = NULL;

	for (i = 0; i < pb_graph_node->num_input_ports; i++) {
		for (j = 0; j < pb_graph_node->num_input_pins[i]; j++) {
			hasPattern = FALSE;
			for (k = 0; k < pb_graph_node->input_pins[i][j].num_output_edges; k++) {
                /* Xifan Tang: bypass pack_patterns whose parent mode is disabled_in_packing*/
                /*
                if (TRUE == pb_graph_node->input_pins[i][j].output_edges[k]->interconnect->parent_mode->disabled_in_packing) {
                  continue;
                }
                */
                /* END */
				for (m = 0; m < pb_graph_node->input_pins[i][j].output_edges[k]->num_pack_patterns;	m++) {
					hasPattern = TRUE;
					index =	add_pattern_name_to_hash(nhash,	
                                                     pb_graph_node->input_pins[i][j].output_edges[k]->pack_pattern_names[m],
                                                     ncount);
					if (pb_graph_node->input_pins[i][j].output_edges[k]->pack_pattern_indices == NULL) {
						pb_graph_node->input_pins[i][j].output_edges[k]->pack_pattern_indices = (int*) my_malloc(pb_graph_node->input_pins[i][j].output_edges[k]->num_pack_patterns * sizeof(int));
					}
					pb_graph_node->input_pins[i][j].output_edges[k]->pack_pattern_indices[m] = index;
				}								
			}
			if (hasPattern == TRUE) {
				forward_infer_pattern(&pb_graph_node->input_pins[i][j]);
				backward_infer_pattern(&pb_graph_node->input_pins[i][j]);
			}
		}
	}

	for (i = 0; i < pb_graph_node->num_output_ports; i++) {
		for (j = 0; j < pb_graph_node->num_output_pins[i]; j++) {
			hasPattern = FALSE;
			for (k = 0; k < pb_graph_node->output_pins[i][j].num_output_edges; k++) {
                /* Xifan Tang: bypass pack_patterns whose parent mode is disabled_in_packing*/
                /*
                if (TRUE == pb_graph_node->output_pins[i][j].output_edges[k]->interconnect->parent_mode->disabled_in_packing) {
                  continue;
                }
                */
                /* END */
				for (m = 0;	m < pb_graph_node->output_pins[i][j].output_edges[k]->num_pack_patterns; m++) {
					hasPattern = TRUE;
					index =	add_pattern_name_to_hash(nhash,
                 									 pb_graph_node->output_pins[i][j].output_edges[k]->pack_pattern_names[m],
									                 ncount);
					if (pb_graph_node->output_pins[i][j].output_edges[k]->pack_pattern_indices == NULL) {
						pb_graph_node->output_pins[i][j].output_edges[k]->pack_pattern_indices = (int*) my_malloc(pb_graph_node->output_pins[i][j].output_edges[k]->num_pack_patterns* sizeof(int));
					}
					pb_graph_node->output_pins[i][j].output_edges[k]->pack_pattern_indices[m] =	index;
				}
			}
			if (hasPattern == TRUE) {
				forward_infer_pattern(&pb_graph_node->output_pins[i][j]);
				backward_infer_pattern(&pb_graph_node->output_pins[i][j]);
			}
		}
	}

	for (i = 0; i < pb_graph_node->num_clock_ports; i++) {
		for (j = 0; j < pb_graph_node->num_clock_pins[i]; j++) {
			hasPattern = FALSE;
			for (k = 0; k < pb_graph_node->clock_pins[i][j].num_output_edges; k++) {
                /* Xifan Tang: bypass pack_patterns whose parent mode is disabled_in_packing*/
                /*
                if (TRUE == pb_graph_node->clock_pins[i][j].output_edges[k]->interconnect->parent_mode->disabled_in_packing) {
                  continue;
                }
                */
                /* END */
				for (m = 0;	m < pb_graph_node->clock_pins[i][j].output_edges[k]->num_pack_patterns;	m++) {
					hasPattern = TRUE;
					index =	add_pattern_name_to_hash(nhash,
													pb_graph_node->clock_pins[i][j].output_edges[k]->pack_pattern_names[m],
													ncount);
					if (pb_graph_node->clock_pins[i][j].output_edges[k]->pack_pattern_indices == NULL) {
						pb_graph_node->clock_pins[i][j].output_edges[k]->pack_pattern_indices = (int*) my_malloc(pb_graph_node->clock_pins[i][j].output_edges[k]->num_pack_patterns	* sizeof(int));
					}
					pb_graph_node->clock_pins[i][j].output_edges[k]->pack_pattern_indices[m] = index;
				}
			}
			if (hasPattern == TRUE) {
				forward_infer_pattern(&pb_graph_node->clock_pins[i][j]);
				backward_infer_pattern(&pb_graph_node->clock_pins[i][j]);
			}
		}
	}

	for (i = 0; i < pb_graph_node->pb_type->num_modes; i++) {
		for (j = 0; j < pb_graph_node->pb_type->modes[i].num_pb_type_children; j++) {
			for (k = 0; k < pb_graph_node->pb_type->modes[i].pb_type_children[j].num_pb; k++) {
				discover_pattern_names_in_pb_graph_node(&pb_graph_node->child_pb_graph_nodes[i][j][k], nhash, ncount);
			}
		}
	}
}

/**
 * In obvious cases where a pattern edge has only one path to go, set that path to be inferred 
 */
static void forward_infer_pattern(INOUTP t_pb_graph_pin *pb_graph_pin) {
	if (pb_graph_pin->num_output_edges == 1 && pb_graph_pin->output_edges[0]->num_pack_patterns == 0 && pb_graph_pin->output_edges[0]->infer_pattern == FALSE) {
		pb_graph_pin->output_edges[0]->infer_pattern = TRUE;
		if (pb_graph_pin->output_edges[0]->num_output_pins == 1) {
			forward_infer_pattern(pb_graph_pin->output_edges[0]->output_pins[0]);
		}
	}
}
static void backward_infer_pattern(INOUTP t_pb_graph_pin *pb_graph_pin) {
	if (pb_graph_pin->num_input_edges == 1 && pb_graph_pin->input_edges[0]->num_pack_patterns == 0 && pb_graph_pin->input_edges[0]->infer_pattern == FALSE) {
		pb_graph_pin->input_edges[0]->infer_pattern = TRUE;
		if (pb_graph_pin->input_edges[0]->num_input_pins == 1) {
			backward_infer_pattern(pb_graph_pin->input_edges[0]->input_pins[0]);
		}
	}
}

/**
 * Allocates memory for models and loads the name of the packing pattern so that it can be identified and loaded with
 * more complete information later
 */
static t_pack_patterns *alloc_and_init_pattern_list_from_hash(INP int ncount,
		INOUTP struct s_hash **nhash) {
	t_pack_patterns *nlist;
	struct s_hash_iterator hash_iter;
	struct s_hash *curr_pattern;

	nlist = (t_pack_patterns*)my_calloc(ncount, sizeof(t_pack_patterns));

	hash_iter = start_hash_table_iterator();
	curr_pattern = get_next_hash(nhash, &hash_iter);
	while (curr_pattern != NULL) {
		assert(nlist[curr_pattern->index].name == NULL);
		nlist[curr_pattern->index].name = my_strdup(curr_pattern->name);
		nlist[curr_pattern->index].root_block = NULL;
		nlist[curr_pattern->index].is_chain = FALSE;
		nlist[curr_pattern->index].index = curr_pattern->index;
		curr_pattern = get_next_hash(nhash, &hash_iter);
	}
	return nlist;
}

void free_list_of_pack_patterns(INP t_pack_patterns *list_of_pack_patterns, INP int num_packing_patterns) {
	int i, j, num_pack_pattern_blocks;
	t_pack_pattern_block **pattern_block_list;
	if (list_of_pack_patterns != NULL) {
		for (i = 0; i < num_packing_patterns; i++) {
			num_pack_pattern_blocks = list_of_pack_patterns[i].num_blocks;
			pattern_block_list = (t_pack_pattern_block **)my_calloc(num_pack_pattern_blocks, sizeof(t_pack_pattern_block *));
			free(list_of_pack_patterns[i].name);
			free(list_of_pack_patterns[i].is_block_optional);
			free_pack_pattern(list_of_pack_patterns[i].root_block, pattern_block_list);
			for (j = 0; j < num_pack_pattern_blocks; j++) {
				free(pattern_block_list[j]);
			}
			free(pattern_block_list);
		}
		free(list_of_pack_patterns);
	}
}

/**
 * Locate first edge that belongs to pattern index 
 */
static t_pb_graph_edge * find_expansion_edge_of_pattern(INP int pattern_index,
		INP t_pb_graph_node *pb_graph_node) {
	int i, j, k, m;
	t_pb_graph_edge * edge;
	/* Iterate over all edges to discover if an edge in current physical block belongs to a pattern 
	 If edge does, then return that edge
	 */

	if (pb_graph_node == NULL) {
		return NULL;
	}

	for (i = 0; i < pb_graph_node->num_input_ports; i++) {
		for (j = 0; j < pb_graph_node->num_input_pins[i]; j++) {
			for (k = 0; k < pb_graph_node->input_pins[i][j].num_output_edges; k++) {
				for (m = 0;	m < pb_graph_node->input_pins[i][j].output_edges[k]->num_pack_patterns;	m++) {
					if (pb_graph_node->input_pins[i][j].output_edges[k]->pack_pattern_indices[m] == pattern_index) {
						return pb_graph_node->input_pins[i][j].output_edges[k];
					}
				}
			}
		}
	}

	for (i = 0; i < pb_graph_node->num_output_ports; i++) {
		for (j = 0; j < pb_graph_node->num_output_pins[i]; j++) {
			for (k = 0; k < pb_graph_node->output_pins[i][j].num_output_edges; k++) {
				for (m = 0;	m < pb_graph_node->output_pins[i][j].output_edges[k]->num_pack_patterns; m++) {
					if (pb_graph_node->output_pins[i][j].output_edges[k]->pack_pattern_indices[m] == pattern_index) {
						return pb_graph_node->output_pins[i][j].output_edges[k];
					}
				}
			}
		}
	}

	for (i = 0; i < pb_graph_node->num_clock_ports; i++) {
		for (j = 0; j < pb_graph_node->num_clock_pins[i]; j++) {
			for (k = 0; k < pb_graph_node->clock_pins[i][j].num_output_edges; k++) {
				for (m = 0;	m < pb_graph_node->clock_pins[i][j].output_edges[k]->num_pack_patterns; m++) {
					if (pb_graph_node->clock_pins[i][j].output_edges[k]->pack_pattern_indices[m] == pattern_index) {
						return pb_graph_node->clock_pins[i][j].output_edges[k];
					}
				}
			}
		}
	}
    /* Xifan TANG's note: Go recursively downto the children pb_graph_node*/
	for (i = 0; i < pb_graph_node->pb_type->num_modes; i++) {
		for (j = 0; j < pb_graph_node->pb_type->modes[i].num_pb_type_children; j++) {
			for (k = 0; k < pb_graph_node->pb_type->modes[i].pb_type_children[j].num_pb; k++) {
				edge = find_expansion_edge_of_pattern(pattern_index, &pb_graph_node->child_pb_graph_nodes[i][j][k]);
				if (edge != NULL) {
					return edge;
				}
			}
		}
	}
	return NULL;
}

/** 
 * Find if receiver of edge is in the same pattern, if yes, add to pattern
 *  Convention: Connections are made on backward expansion only (to make future multi-fanout support easier) so this function will not update connections
 */
static void forward_expand_pack_pattern_from_edge(
		INP t_pb_graph_edge* expansion_edge,
		INOUTP t_pack_patterns *list_of_packing_patterns,
		INP int curr_pattern_index, INP int *L_num_blocks, INOUTP boolean make_root_of_chain) {
	int i, j, k;
	int iport, ipin, iedge;
	boolean found; /* Error checking, ensure only one fan-out for each pattern net */
	t_pack_pattern_block *destination_block = NULL;
	t_pb_graph_node *destination_pb_graph_node = NULL;

	found = expansion_edge->infer_pattern;
	for (i = 0;	!found && i < expansion_edge->num_pack_patterns; i++) {
		if (expansion_edge->pack_pattern_indices[i] == curr_pattern_index) {
			found = TRUE;
		}
	}
	if (!found) {
		return;
	}

	found = FALSE;
	for (i = 0; i < expansion_edge->num_output_pins; i++) {
		if (expansion_edge->output_pins[i]->parent_node->pb_type->num_modes	== 0) {
			destination_pb_graph_node = expansion_edge->output_pins[i]->parent_node;
			assert(found == FALSE);
			/* Check assumption that each forced net has only one fan-out */
			/* This is the destination node */
			found = TRUE;

			/* If this pb_graph_node is part not of the current pattern index, put it in and expand all its edges */
			if (destination_pb_graph_node->temp_scratch_pad == NULL
				|| ((t_pack_pattern_block*) destination_pb_graph_node->temp_scratch_pad)->pattern_index != curr_pattern_index) {
				destination_block = (t_pack_pattern_block*)my_calloc(1, sizeof(t_pack_pattern_block));
				list_of_packing_patterns[curr_pattern_index].base_cost += compute_primitive_base_cost(destination_pb_graph_node);
				destination_block->block_id = *L_num_blocks;
				(*L_num_blocks)++;
				destination_pb_graph_node->temp_scratch_pad = (void *) destination_block;
				destination_block->pattern_index = curr_pattern_index;
				destination_block->pb_type = destination_pb_graph_node->pb_type;
				for (iport = 0;	iport < destination_pb_graph_node->num_input_ports; iport++) {
					for (ipin = 0; ipin < destination_pb_graph_node->num_input_pins[iport];	ipin++) {
						for (iedge = 0;	iedge < destination_pb_graph_node->input_pins[iport][ipin].num_input_edges;	iedge++) {
							backward_expand_pack_pattern_from_edge(
									destination_pb_graph_node->input_pins[iport][ipin].input_edges[iedge],
									list_of_packing_patterns,
									curr_pattern_index,
									&destination_pb_graph_node->input_pins[iport][ipin],
									destination_block, L_num_blocks);
						}
					}
				}
				for (iport = 0;	iport < destination_pb_graph_node->num_output_ports; iport++) {
					for (ipin = 0; ipin < destination_pb_graph_node->num_output_pins[iport]; ipin++) {
						for (iedge = 0;	iedge < destination_pb_graph_node->output_pins[iport][ipin].num_output_edges; iedge++) {
							forward_expand_pack_pattern_from_edge(
									destination_pb_graph_node->output_pins[iport][ipin].output_edges[iedge],
									list_of_packing_patterns,
									curr_pattern_index, L_num_blocks, FALSE);
						}
					}
				}
				for (iport = 0;	iport < destination_pb_graph_node->num_clock_ports;	iport++) {
					for (ipin = 0;ipin < destination_pb_graph_node->num_clock_pins[iport]; ipin++) {
						for (iedge = 0;	iedge < destination_pb_graph_node->clock_pins[iport][ipin].num_input_edges;	iedge++) {
							backward_expand_pack_pattern_from_edge(
									destination_pb_graph_node->clock_pins[iport][ipin].input_edges[iedge],
									list_of_packing_patterns,
									curr_pattern_index,
									&destination_pb_graph_node->clock_pins[iport][ipin],
									destination_block, L_num_blocks);
						}
					}
				}
			} 
			if (((t_pack_pattern_block*) destination_pb_graph_node->temp_scratch_pad)->pattern_index == curr_pattern_index) {
				if(make_root_of_chain == TRUE) {
					list_of_packing_patterns[curr_pattern_index].chain_root_pin = expansion_edge->output_pins[i];
					list_of_packing_patterns[curr_pattern_index].root_block = destination_block;
				}
			}
		} else {
			for (j = 0; j < expansion_edge->output_pins[i]->num_output_edges; j++) {
				if (expansion_edge->output_pins[i]->output_edges[j]->infer_pattern == TRUE) {
					forward_expand_pack_pattern_from_edge(
							expansion_edge->output_pins[i]->output_edges[j],
							list_of_packing_patterns, curr_pattern_index,
							L_num_blocks, make_root_of_chain);
				} else {
					for (k = 0;	k < expansion_edge->output_pins[i]->output_edges[j]->num_pack_patterns;	k++) {
						if (expansion_edge->output_pins[i]->output_edges[j]->pack_pattern_indices[k] == curr_pattern_index) {
							if (found == FALSE) {
							assert(found == FALSE);
                            }
							/* Check assumption that each forced net has only one fan-out */
							found = TRUE;
							forward_expand_pack_pattern_from_edge(
									expansion_edge->output_pins[i]->output_edges[j],
									list_of_packing_patterns,
									curr_pattern_index, L_num_blocks, make_root_of_chain);
						}
					}
				}
			}
		}
	}

}

/** 
 * Find if driver of edge is in the same pattern, if yes, add to pattern
 *  Convention: Connections are made on backward expansion only (to make future multi-fanout support easier) so this function must update both source and destination blocks
 */
static void backward_expand_pack_pattern_from_edge(
		INP t_pb_graph_edge* expansion_edge,
		INOUTP t_pack_patterns *list_of_packing_patterns,
		INP int curr_pattern_index, INP t_pb_graph_pin *destination_pin,
		INP t_pack_pattern_block *destination_block, INP int *L_num_blocks) {
	int i, j, k;
	int iport, ipin, iedge;
	boolean found; /* Error checking, ensure only one fan-out for each pattern net */
	t_pack_pattern_block *source_block = NULL;
	t_pb_graph_node *source_pb_graph_node = NULL;
	t_pack_pattern_connections *pack_pattern_connection = NULL;

	found = expansion_edge->infer_pattern;
	for (i = 0;	!found && i < expansion_edge->num_pack_patterns; i++) {
		if (expansion_edge->pack_pattern_indices[i] == curr_pattern_index) {
			found = TRUE;
		}
	}
	if (!found) {
		return;
	}

	found = FALSE;
	for (i = 0; i < expansion_edge->num_input_pins; i++) {
		if (expansion_edge->input_pins[i]->parent_node->pb_type->num_modes == 0) {
			source_pb_graph_node = expansion_edge->input_pins[i]->parent_node;
			assert(found == FALSE);
			/* Check assumption that each forced net has only one fan-out */
			/* This is the source node for destination */
			found = TRUE;

			/* If this pb_graph_node is part not of the current pattern index, put it in and expand all its edges */
			source_block = (t_pack_pattern_block*) source_pb_graph_node->temp_scratch_pad;
			if (source_block == NULL
			   || source_block->pattern_index != curr_pattern_index) {
				source_block = (t_pack_pattern_block *)my_calloc(1, sizeof(t_pack_pattern_block));
				source_block->block_id = *L_num_blocks;
				(*L_num_blocks)++;
				list_of_packing_patterns[curr_pattern_index].base_cost += compute_primitive_base_cost(source_pb_graph_node);
				source_pb_graph_node->temp_scratch_pad = (void *) source_block;
				source_block->pattern_index = curr_pattern_index;
				source_block->pb_type = source_pb_graph_node->pb_type;

				if (list_of_packing_patterns[curr_pattern_index].root_block	== NULL) {
					list_of_packing_patterns[curr_pattern_index].root_block = source_block;
				}

				for (iport = 0; iport < source_pb_graph_node->num_input_ports; iport++) {
					for (ipin = 0; ipin < source_pb_graph_node->num_input_pins[iport]; ipin++) {
						for (iedge = 0;	iedge < source_pb_graph_node->input_pins[iport][ipin].num_input_edges; iedge++) {
							backward_expand_pack_pattern_from_edge(
									source_pb_graph_node->input_pins[iport][ipin].input_edges[iedge],
									list_of_packing_patterns,
									curr_pattern_index,
									&source_pb_graph_node->input_pins[iport][ipin],
									source_block, L_num_blocks);
						}
					}
				}
				for (iport = 0; iport < source_pb_graph_node->num_output_ports;	iport++) {
					for (ipin = 0; ipin < source_pb_graph_node->num_output_pins[iport];	ipin++) {
						for (iedge = 0;	iedge < source_pb_graph_node->output_pins[iport][ipin].num_output_edges; iedge++) {
							forward_expand_pack_pattern_from_edge(
									source_pb_graph_node->output_pins[iport][ipin].output_edges[iedge],
									list_of_packing_patterns,
									curr_pattern_index, L_num_blocks, FALSE);
						}
					}
				}
				for (iport = 0; iport < source_pb_graph_node->num_clock_ports; iport++) {
					for (ipin = 0; ipin < source_pb_graph_node->num_clock_pins[iport]; ipin++) {
						for (iedge = 0;	iedge < source_pb_graph_node->clock_pins[iport][ipin].num_input_edges; iedge++) {
							backward_expand_pack_pattern_from_edge(
									source_pb_graph_node->clock_pins[iport][ipin].input_edges[iedge],
									list_of_packing_patterns,
									curr_pattern_index,
									&source_pb_graph_node->clock_pins[iport][ipin],
									source_block, L_num_blocks);
						}
					}
				}
			}
			if (destination_pin != NULL) {
				assert(((t_pack_pattern_block*)source_pb_graph_node->temp_scratch_pad)->pattern_index == curr_pattern_index);
				source_block = (t_pack_pattern_block*) source_pb_graph_node->temp_scratch_pad;
				pack_pattern_connection = (t_pack_pattern_connections *)my_calloc(1, sizeof(t_pack_pattern_connections));
				pack_pattern_connection->from_block = source_block;
				pack_pattern_connection->from_pin =	expansion_edge->input_pins[i];
				pack_pattern_connection->to_block = destination_block;
				pack_pattern_connection->to_pin = destination_pin;
				pack_pattern_connection->next = source_block->connections;
				source_block->connections = pack_pattern_connection;

				pack_pattern_connection = (t_pack_pattern_connections *)my_calloc(1, sizeof(t_pack_pattern_connections));
				pack_pattern_connection->from_block = source_block;
				pack_pattern_connection->from_pin = expansion_edge->input_pins[i];
				pack_pattern_connection->to_block = destination_block;
				pack_pattern_connection->to_pin = destination_pin;
				pack_pattern_connection->next = destination_block->connections;
				destination_block->connections = pack_pattern_connection;

				if (source_block == destination_block) {
					vpr_printf(TIO_MESSAGE_ERROR, "Invalid packing pattern defined. Source and destination block are the same (%s).\n",
							source_block->pb_type->name);
				}
			}
		} else {
			if(expansion_edge->input_pins[i]->num_input_edges == 0) {
				if(expansion_edge->input_pins[i]->parent_node->pb_type->parent_mode == NULL) {
					/* This pack pattern extends to CLB input pin, thus it extends across multiple logic blocks, treat as a chain */
					list_of_packing_patterns[curr_pattern_index].is_chain = TRUE;
					forward_expand_pack_pattern_from_edge(
									expansion_edge,
									list_of_packing_patterns,
									curr_pattern_index, L_num_blocks, TRUE);
				}
			} else {
				for (j = 0; j < expansion_edge->input_pins[i]->num_input_edges;	j++) {
					if (expansion_edge->input_pins[i]->input_edges[j]->infer_pattern == TRUE) {
						backward_expand_pack_pattern_from_edge(
								expansion_edge->input_pins[i]->input_edges[j],
								list_of_packing_patterns, curr_pattern_index,
								destination_pin, destination_block, L_num_blocks);
					} else {
						for (k = 0;	k < expansion_edge->input_pins[i]->input_edges[j]->num_pack_patterns; k++) {
							if (expansion_edge->input_pins[i]->input_edges[j]->pack_pattern_indices[k] == curr_pattern_index) {
								if (found == FALSE) {
								assert(found == FALSE);
                                }
								/* Check assumption that each forced net has only one fan-out */
								found = TRUE;
								backward_expand_pack_pattern_from_edge(
										expansion_edge->input_pins[i]->input_edges[j],
										list_of_packing_patterns,
										curr_pattern_index, destination_pin,
										destination_block, L_num_blocks);
							}
						}
					}
				}
			}
		}
	}
}

/**
 * Pre-pack atoms in netlist to molecules
 * 1.  Single atoms are by definition a molecule.
 * 2.  Forced pack molecules are groupings of atoms that matches a t_pack_pattern definition.
 * 3.  Chained molecules are molecules that follow a carry-chain style pattern: ie. a single linear chain that can be split across multiple complex blocks
 */
t_pack_molecule *alloc_and_load_pack_molecules(
		INP t_pack_patterns *list_of_pack_patterns,
		INP int num_packing_patterns, OUTP int *num_pack_molecule) {
	int i, j, best_pattern;
	t_pack_molecule *list_of_molecules_head;
	t_pack_molecule *cur_molecule;
	boolean *is_used;

	is_used = (boolean*)my_calloc(num_packing_patterns, sizeof(boolean));

    /* Xifan Tang: initialize the pattern usage ! Mark used for patterns that belongs to modes disabled_in_packing*/
	for (i = 0; i < num_packing_patterns; i++) {
      if (TRUE == list_of_pack_patterns[i].root_block->pb_type->parent_mode->disabled_in_packing) {
        is_used[i] = TRUE;
      }
    }
    /* END */

	cur_molecule = list_of_molecules_head = NULL;

	/* Find forced pack patterns */
	/* Simplifying assumptions: Each atom can map to at most one molecule, use first-fit mapping based on priority of pattern */
	/* TODO: Need to investigate better mapping strategies than first-fit */
	for (i = 0; i < num_packing_patterns; i++) {
		best_pattern = 0;
		for(j = 1; j < num_packing_patterns; j++) {
			if(is_used[best_pattern]) {
				best_pattern = j;
			} else if (is_used[j] == FALSE && compare_pack_pattern(&list_of_pack_patterns[j], &list_of_pack_patterns[best_pattern]) == 1) {
				best_pattern = j;
			}
		}
        /* Xifan Tang: we may not found an usused pattern */
        if (TRUE == is_used[best_pattern]) {
          continue;
        }
        /* END */
		assert(is_used[best_pattern] == FALSE);
		is_used[best_pattern] = TRUE;
		for (j = 0; j < num_logical_blocks; j++) {
			cur_molecule = try_create_molecule(list_of_pack_patterns, best_pattern, j);
			if (cur_molecule != NULL) {
				cur_molecule->next = list_of_molecules_head;
				/* In the event of multiple molecules with the same logical block pattern, bias to use the molecule with less costly physical resources first */
				/* TODO: Need to normalize magical number 100 */
				cur_molecule->base_gain = cur_molecule->num_blocks - (cur_molecule->pack_pattern->base_cost / 100);
				list_of_molecules_head = cur_molecule;
				if(logical_block[j].packed_molecules == NULL || logical_block[j].packed_molecules->data_vptr != cur_molecule) {
					/* molecule did not cover current atom (possibly because molecule created is part of a long chain that extends past multiple logic blocks), try again */
					j--;
				}
			}
		}
	}
	free(is_used);

	/* List all logical blocks as a molecule for blocks that do not belong to any molecules.
	 This allows the packer to be consistent as it now packs molecules only instead of atoms and molecules

	 If a block belongs to a molecule, then carrying the single atoms around can make the packing problem
	 more difficult because now it needs to consider splitting molecules.
	 */
	for (i = 0; i < num_logical_blocks; i++) {
		logical_block[i].expected_lowest_cost_primitive = get_expected_lowest_cost_primitive_for_logical_block(i);
		if (logical_block[i].packed_molecules == NULL) {
			cur_molecule = (t_pack_molecule*) my_calloc(1,
					sizeof(t_pack_molecule));
			cur_molecule->valid = TRUE;
			cur_molecule->type = MOLECULE_SINGLE_ATOM;
			cur_molecule->num_blocks = 1;
			cur_molecule->root = 0;
			cur_molecule->num_ext_inputs = logical_block[i].used_input_pins;
			cur_molecule->chain_pattern = NULL;
			cur_molecule->pack_pattern = NULL;
			cur_molecule->logical_block_ptrs = (t_logical_block**) my_malloc(1 * sizeof(t_logical_block*));
			cur_molecule->logical_block_ptrs[0] = &logical_block[i];
			cur_molecule->next = list_of_molecules_head;
			cur_molecule->base_gain = 1;
			list_of_molecules_head = cur_molecule;

			logical_block[i].packed_molecules = (struct s_linked_vptr*) my_calloc(1,
					sizeof(struct s_linked_vptr));
			logical_block[i].packed_molecules->data_vptr = (void*) cur_molecule;
		}
	}

	if (getEchoEnabled() && isEchoFileEnabled(E_ECHO_PRE_PACKING_MOLECULES_AND_PATTERNS)) {
		print_pack_molecules(getEchoFileName(E_ECHO_PRE_PACKING_MOLECULES_AND_PATTERNS),
				list_of_pack_patterns, num_packing_patterns,
				list_of_molecules_head);
	}

	return list_of_molecules_head;
}


static void free_pack_pattern(INOUTP t_pack_pattern_block *pattern_block, INOUTP t_pack_pattern_block **pattern_block_list) {
	t_pack_pattern_connections *connection, *next;
	if (pattern_block->block_id == OPEN) {
		/* already traversed, return */
		return; 
	}
	pattern_block_list[pattern_block->block_id] = pattern_block;
	pattern_block->block_id = OPEN;
	connection = pattern_block->connections;
	while (connection) {
		free_pack_pattern(connection->from_block, pattern_block_list);
		free_pack_pattern(connection->to_block, pattern_block_list);
		next = connection->next;
		free(connection);
		connection = next;
	}
}

/**
 * Given a pattern and a logical block to serve as the root block, determine if the candidate logical block serving as the root node matches the pattern
 * If yes, return the molecule with this logical block as the root, if not, return NULL
 * Limitations: Currently assumes that forced pack nets must be single-fanout as this covers all the reasonable architectures we wanted
 More complicated structures should probably be handled either downstream (general packing) or upstream (in tech mapping)
 *              If this limitation is too constraining, code is designed so that this limitation can be removed
 * Side Effect: If successful, link atom to molecule
 */
static t_pack_molecule *try_create_molecule(
		INP t_pack_patterns *list_of_pack_patterns, INP int pack_pattern_index,
		INP int block_index) {
	int i;
	t_pack_molecule *molecule;
	struct s_linked_vptr *molecule_linked_list;

	molecule = (t_pack_molecule*)my_calloc(1, sizeof(t_pack_molecule));
	molecule->valid = TRUE;
	molecule->type = MOLECULE_FORCED_PACK;
	molecule->pack_pattern = &list_of_pack_patterns[pack_pattern_index];
	molecule->logical_block_ptrs = (t_logical_block **)my_calloc(molecule->pack_pattern->num_blocks,
			sizeof(t_logical_block *));
	molecule->num_blocks = list_of_pack_patterns[pack_pattern_index].num_blocks;
	molecule->root = list_of_pack_patterns[pack_pattern_index].root_block->block_id;
	molecule->num_ext_inputs = 0;

	if(list_of_pack_patterns[pack_pattern_index].is_chain == TRUE) {
		/* A chain pattern extends beyond a single logic block so we must find the block_index that matches with the portion of a chain for this particular logic block */
		block_index = find_new_root_atom_for_chain(block_index, &list_of_pack_patterns[pack_pattern_index]);
	}

	if (block_index != OPEN && try_expand_molecule(molecule, block_index, molecule->pack_pattern->root_block) == TRUE) {
		/* Success! commit module */
		for (i = 0; i < molecule->pack_pattern->num_blocks; i++) {
			if(molecule->logical_block_ptrs[i] == NULL) {
				assert(list_of_pack_patterns[pack_pattern_index].is_block_optional[i] == TRUE);
				continue;
			}			
			molecule_linked_list = (struct s_linked_vptr*) my_calloc(1, sizeof(struct s_linked_vptr));
			molecule_linked_list->data_vptr = (void *) molecule;
			molecule_linked_list->next = molecule->logical_block_ptrs[i]->packed_molecules;
			molecule->logical_block_ptrs[i]->packed_molecules =	molecule_linked_list;
		}
	} else {
		/* Does not match pattern, free molecule */
		free(molecule->logical_block_ptrs);
		free(molecule);
		molecule = NULL;
	}

	return molecule;
}

/**
 * Determine if logical block can match with the pattern to form a molecule
 * return TRUE if it matches, return FALSE otherwise
 */
static boolean try_expand_molecule(INOUTP t_pack_molecule *molecule,
		INP int logical_block_index,
		INP t_pack_pattern_block *current_pattern_block) {
	int iport, ipin, inet;
	boolean success;
	boolean is_optional;
	boolean *is_block_optional;
	t_pack_pattern_connections *cur_pack_pattern_connection;
	is_block_optional = molecule->pack_pattern->is_block_optional;
	is_optional = is_block_optional[current_pattern_block->block_id];

		/* If the block in the pattern has already been visited, then there is no need to revisit it */
	if (molecule->logical_block_ptrs[current_pattern_block->block_id] != NULL) {
		if (molecule->logical_block_ptrs[current_pattern_block->block_id]
				!= &logical_block[logical_block_index]) {
			/* Mismatch between the visited block and the current block implies that the current netlist structure does not match the expected pattern, return whether or not this matters */
			return is_optional;
		} else {
			molecule->num_ext_inputs--; /* This block is revisited, implies net is entirely internal to molecule, reduce count */
			return TRUE;
		}
	}

	/* This node has never been visited */
	/* Simplifying assumption: An atom can only map to one molecule */
	if(logical_block[logical_block_index].packed_molecules != NULL) {
		/* This block is already in a molecule, return whether or not this matters */
		return is_optional;
	}

	if (primitive_type_feasible(logical_block_index,
			current_pattern_block->pb_type)) {

		success = TRUE;
		/* If the primitive types match, store it, expand it and explore neighbouring nodes */
		molecule->logical_block_ptrs[current_pattern_block->block_id] =
				&logical_block[logical_block_index]; /* store that this node has been visited */
		molecule->num_ext_inputs +=
				logical_block[logical_block_index].used_input_pins;
		
		cur_pack_pattern_connection = current_pattern_block->connections;
		while (cur_pack_pattern_connection != NULL && success == TRUE) {
			if (cur_pack_pattern_connection->from_block
					== current_pattern_block) {
				/* find net corresponding to pattern */
				iport =
						cur_pack_pattern_connection->from_pin->port->model_port->index;
				ipin = cur_pack_pattern_connection->from_pin->pin_number;
				inet =
						logical_block[logical_block_index].output_nets[iport][ipin];

				/* Check if net is valid */
				if (inet == OPEN || vpack_net[inet].num_sinks != 1) { /* One fanout assumption */
					success = is_block_optional[cur_pack_pattern_connection->to_block->block_id];
				} else {
					success = try_expand_molecule(molecule,
							vpack_net[inet].node_block[1],
							cur_pack_pattern_connection->to_block);
				}
			} else {
				assert(
						cur_pack_pattern_connection->to_block == current_pattern_block);
				/* find net corresponding to pattern */
				iport =
						cur_pack_pattern_connection->to_pin->port->model_port->index;
				ipin = cur_pack_pattern_connection->to_pin->pin_number;
				if (cur_pack_pattern_connection->to_pin->port->model_port->is_clock) {
					inet = logical_block[logical_block_index].clock_net;
				} else {
					inet =
							logical_block[logical_block_index].input_nets[iport][ipin];
				}
				/* Check if net is valid */
				if (inet == OPEN || vpack_net[inet].num_sinks != 1) { /* One fanout assumption */
					success = is_block_optional[cur_pack_pattern_connection->from_block->block_id];
				} else {
					success = try_expand_molecule(molecule,
							vpack_net[inet].node_block[0],
							cur_pack_pattern_connection->from_block);
				}
			}
			cur_pack_pattern_connection = cur_pack_pattern_connection->next;
		}
	} else {
		success = is_optional;
	}

	return success;
}

static void print_pack_molecules(INP const char *fname,
		INP t_pack_patterns *list_of_pack_patterns, INP int num_pack_patterns,
		INP t_pack_molecule *list_of_molecules) {
	int i;
	FILE *fp;
	t_pack_molecule *list_of_molecules_current;

	fp = my_fopen(fname, "w", 0);
	fprintf(fp, "# of pack patterns %d\n", num_pack_patterns);
		
	for (i = 0; i < num_pack_patterns; i++) {
		fprintf(fp, "pack pattern index %d block count %d name %s root %s\n",
				list_of_pack_patterns[i].index,
				list_of_pack_patterns[i].num_blocks,
				list_of_pack_patterns[i].name,
				list_of_pack_patterns[i].root_block->pb_type->name);
	}

	list_of_molecules_current = list_of_molecules;
	while (list_of_molecules_current != NULL) {
		if (list_of_molecules_current->type == MOLECULE_SINGLE_ATOM) {
			fprintf(fp, "\nmolecule type: atom\n");
			fprintf(fp, "\tpattern index %d: logical block [%d] name %s\n", i,
					list_of_molecules_current->logical_block_ptrs[0]->index,
					list_of_molecules_current->logical_block_ptrs[0]->name);
		} else if (list_of_molecules_current->type == MOLECULE_FORCED_PACK) {
			fprintf(fp, "\nmolecule type: %s\n",
					list_of_molecules_current->pack_pattern->name);
			for (i = 0; i < list_of_molecules_current->pack_pattern->num_blocks;
					i++) {
				if(list_of_molecules_current->logical_block_ptrs[i] == NULL) {
					fprintf(fp, "\tpattern index %d: empty \n",	i);
				} else {
					fprintf(fp, "\tpattern index %d: logical block [%d] name %s",
						i,
						list_of_molecules_current->logical_block_ptrs[i]->index,
						list_of_molecules_current->logical_block_ptrs[i]->name);
					if(list_of_molecules_current->pack_pattern->root_block->block_id == i) {
						fprintf(fp, " root node\n");
					} else {
						fprintf(fp, "\n");
					}
				}
			}
		} else {
			assert(0);
		}
		list_of_molecules_current = list_of_molecules_current->next;
	}

	fclose(fp);
}

/* Search through all primitives and return the lowest cost primitive that fits this logical block */
static t_pb_graph_node *get_expected_lowest_cost_primitive_for_logical_block(INP int ilogical_block) {
	int i;
	float cost, best_cost;
	t_pb_graph_node *current, *best;

	best_cost = UNDEFINED;
	best = NULL;
	current = NULL;
	for(i = 0; i < num_types; i++) {
		cost = UNDEFINED;
		current = get_expected_lowest_cost_primitive_for_logical_block_in_pb_graph_node(ilogical_block, type_descriptors[i].pb_graph_head, &cost);
		if(cost != UNDEFINED) {
			if(best_cost == UNDEFINED || best_cost > cost) {
				best_cost = cost;
				best = current;
			}
		}
	}
	return best;
}

static t_pb_graph_node *get_expected_lowest_cost_primitive_for_logical_block_in_pb_graph_node(INP int ilogical_block, INP t_pb_graph_node *curr_pb_graph_node, OUTP float *cost) {
	t_pb_graph_node *best, *cur;
	float cur_cost, best_cost;
	int i, j;

	best = NULL;
	best_cost = UNDEFINED;
	if(curr_pb_graph_node == NULL) {
		return NULL;
	}
	
	if(curr_pb_graph_node->pb_type->blif_model != NULL) {
		if(primitive_type_feasible(ilogical_block, curr_pb_graph_node->pb_type)) {
			cur_cost = compute_primitive_base_cost(curr_pb_graph_node);
			if(best_cost == UNDEFINED || best_cost > cur_cost) {
				best_cost = cur_cost;
				best = curr_pb_graph_node;
			}
		}
	} else {
		for(i = 0; i < curr_pb_graph_node->pb_type->num_modes; i++) {
			for(j = 0; j < curr_pb_graph_node->pb_type->modes[i].num_pb_type_children; j++) {
				*cost = UNDEFINED;
				cur = get_expected_lowest_cost_primitive_for_logical_block_in_pb_graph_node(ilogical_block, &curr_pb_graph_node->child_pb_graph_nodes[i][j][0], cost);
				if(cur != NULL) {
					if(best == NULL || best_cost > *cost) {
						best = cur;
						best_cost = *cost;
					}
				}
			}
		}
	}

	*cost = best_cost;
	return best;
}


/* Determine which of two pack pattern should take priority */
static int compare_pack_pattern(const t_pack_patterns *pattern_a, const t_pack_patterns *pattern_b) {
	float base_gain_a, base_gain_b, diff;

	/* Bigger patterns should take higher priority than smaller patterns because they are harder to fit */
	if (pattern_a->num_blocks > pattern_b->num_blocks) {
		return 1;
	} else if (pattern_a->num_blocks < pattern_b->num_blocks) {
		return -1;
	}

	base_gain_a = pattern_a->base_cost;
	base_gain_b = pattern_b->base_cost;
	diff = base_gain_a - base_gain_b;

	/* Less costly patterns should be used before more costly patterns */
	if (diff < 0) {
		return 1;
	}
	if (diff > 0) {
		return -1;
	}
	return 0;
}

/* A chain can extend across multiple logic blocks.  Must segment the chain to fit in a logic block by identifying the actual atom that forms the root of the new chain.
 * Returns OPEN if this block_index doesn't match up with any chain
 *
 * Assumes that the root of a chain is the primitive that starts the chain or is driven from outside the logic block
 * block_index: index of current atom
 * list_of_pack_pattern: ptr to current chain pattern
 */
static int find_new_root_atom_for_chain(INP int block_index, INP t_pack_patterns *list_of_pack_pattern) {
	int new_index = OPEN;
	t_pb_graph_pin *root_ipin;
	t_pb_graph_node *root_pb_graph_node;
	t_model_ports *model_port;
	int driver_net, driver_block;
	
	assert(list_of_pack_pattern->is_chain == TRUE);
	root_ipin = list_of_pack_pattern->chain_root_pin;
	root_pb_graph_node = root_ipin->parent_node;

	if(primitive_type_feasible(block_index, root_pb_graph_node->pb_type) == FALSE) {
		return OPEN;
	}

    /* Xifan TANG: this is trying to find the root logical_block which is the head of a carry chain */
	/* Assign driver furthest up the chain that matches the root node and is unassigned to a molecule as the root */
	model_port = root_ipin->port->model_port;
	driver_net = logical_block[block_index].input_nets[model_port->index][root_ipin->pin_number];
	if(driver_net == OPEN) {
		/* The current block is the furthest up the chain, return it */
		return block_index;
	}

    /* Xifan TANG: this is trying to find a possible starting logical block, whose preceding block is already assigned
     *             to another molecule
     */
	driver_block = vpack_net[driver_net].node_block[0];
	if(logical_block[driver_block].packed_molecules != NULL) {
		/* Driver is used/invalid, so current block is the furthest up the chain, return it */
		return block_index;
	}

	new_index = find_new_root_atom_for_chain(driver_block, list_of_pack_pattern);
	if(new_index == OPEN) {
		return block_index;
	} else {
		return new_index;
	}
}