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atom_map.cpp
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Thu, Nov 7, 19:10

atom_map.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
#include <math.h>
#include "atom.h"
#include "comm.h"
#include "memory.h"
#include "error.h"
using namespace LAMMPS_NS;
#define EXTRA 1000
/* ----------------------------------------------------------------------
allocate and initialize array or hash table for global -> local map
for array option:
array length = 1 to map_tag_max
set entire array to -1 as initial values
for hash option:
map_nhash = length of hash table
map_nbucket = # of hash buckets, prime larger than map_nhash * 2
so buckets will only be filled with 0 or 1 atoms on average
------------------------------------------------------------------------- */
void Atom::map_init(int check)
{
// check for new map style if max atomID changed (check = 1 = default)
// recreate = 1 if must delete old map and create new map
// recreate = 0 if can re-use old map w/out realloc and just adjust settings
// map_maxarray/map_nhash initially -1, to force recreate even when no atoms
int recreate = 0;
if (check) recreate = map_style_set();
if (map_style == 1 && map_tag_max > map_maxarray) recreate = 1;
else if (map_style == 2 && nlocal+nghost > map_nhash) recreate = 1;
// if not recreating:
// for array, initialize current map_tag_max values
// for hash, set all buckets to empty, put all entries in free list
if (!recreate) {
if (map_style == 1) {
for (int i = 0; i <= map_tag_max; i++) map_array[i] = -1;
} else {
for (int i = 0; i < map_nbucket; i++) map_bucket[i] = -1;
map_nused = 0;
map_free = 0;
for (int i = 0; i < map_nhash; i++) map_hash[i].next = i+1;
map_hash[map_nhash-1].next = -1;
}
// recreating: delete old map and create new one for array or hash
} else {
map_delete();
if (map_style == 1) {
map_maxarray = map_tag_max;
memory->create(map_array,map_maxarray+1,"atom:map_array");
for (int i = 0; i <= map_tag_max; i++) map_array[i] = -1;
} else {
// map_nhash = max # of atoms that can be hashed on this proc
// set to max of ave atoms/proc or atoms I can store
// multiply by 2, require at least 1000
// doubling means hash table will need to be re-init only rarely
int nper = static_cast<int> (natoms/comm->nprocs);
map_nhash = MAX(nper,nmax);
map_nhash *= 2;
map_nhash = MAX(map_nhash,1000);
// map_nbucket = prime just larger than map_nhash
// next_prime() should be fast enough,
// about 10% of odd integers are prime above 1M
map_nbucket = next_prime(map_nhash);
// set all buckets to empty
// set hash to map_nhash in length
// put all hash entries in free list and point them to each other
map_bucket = new int[map_nbucket];
for (int i = 0; i < map_nbucket; i++) map_bucket[i] = -1;
map_hash = new HashElem[map_nhash];
map_nused = 0;
map_free = 0;
for (int i = 0; i < map_nhash; i++) map_hash[i].next = i+1;
map_hash[map_nhash-1].next = -1;
}
}
}
/* ----------------------------------------------------------------------
clear global -> local map for all of my own and ghost atoms
for hash table option:
global ID may not be in table if image atom was already cleared
------------------------------------------------------------------------- */
void Atom::map_clear()
{
if (map_style == 1) {
int nall = nlocal + nghost;
for (int i = 0; i < nall; i++) {
sametag[i] = -1;
map_array[tag[i]] = -1;
}
} else {
int previous,ibucket,index;
tagint global;
int nall = nlocal + nghost;
for (int i = 0; i < nall; i++) {
sametag[i] = -1;
// search for key
// if don't find it, done
previous = -1;
global = tag[i];
ibucket = global % map_nbucket;
index = map_bucket[ibucket];
while (index > -1) {
if (map_hash[index].global == global) break;
previous = index;
index = map_hash[index].next;
}
if (index == -1) continue;
// delete the hash entry and add it to free list
// special logic if entry is 1st in the bucket
if (previous == -1) map_bucket[ibucket] = map_hash[index].next;
else map_hash[previous].next = map_hash[index].next;
map_hash[index].next = map_free;
map_free = index;
map_nused--;
}
}
}
/* ----------------------------------------------------------------------
set global -> local map for all of my own and ghost atoms
loop in reverse order so that nearby images take precedence over far ones
and owned atoms take precedence over images
this enables valid lookups of bond topology atoms
for hash table option:
if hash table too small, re-init
global ID may already be in table if image atom was set
------------------------------------------------------------------------- */
void Atom::map_set()
{
int nall = nlocal + nghost;
if (map_style == 1) {
// possible reallocation of sametag must come before loop over atoms
// since loop sets sametag
if (nall > max_same) {
max_same = nall + EXTRA;
memory->destroy(sametag);
memory->create(sametag,max_same,"atom:sametag");
}
for (int i = nall-1; i >= 0 ; i--) {
sametag[i] = map_array[tag[i]];
map_array[tag[i]] = i;
}
} else {
// if this proc has more atoms than hash table size, call map_init()
// call with 0 since max atomID in system has not changed
// possible reallocation of sametag must come after map_init(),
// b/c map_init() may invoke map_delete(), whacking sametag
if (nall > map_nhash) map_init(0);
if (nall > max_same) {
max_same = nall + EXTRA;
memory->destroy(sametag);
memory->create(sametag,max_same,"atom:sametag");
}
int previous,ibucket,index;
tagint global;
for (int i = nall-1; i >= 0 ; i--) {
sametag[i] = map_find_hash(tag[i]);
// search for key
// if found it, just overwrite local value with index
previous = -1;
global = tag[i];
ibucket = global % map_nbucket;
index = map_bucket[ibucket];
while (index > -1) {
if (map_hash[index].global == global) break;
previous = index;
index = map_hash[index].next;
}
if (index > -1) {
map_hash[index].local = i;
continue;
}
// take one entry from free list
// add the new global/local pair as entry at end of bucket list
// special logic if this entry is 1st in bucket
index = map_free;
map_free = map_hash[map_free].next;
if (previous == -1) map_bucket[ibucket] = index;
else map_hash[previous].next = index;
map_hash[index].global = global;
map_hash[index].local = i;
map_hash[index].next = -1;
map_nused++;
}
}
}
/* ----------------------------------------------------------------------
set global to local map for one atom
for hash table option:
global ID may already be in table if atom was already set
called by Special class
------------------------------------------------------------------------- */
void Atom::map_one(tagint global, int local)
{
if (map_style == 1) map_array[global] = local;
else {
// search for key
// if found it, just overwrite local value with index
int previous = -1;
int ibucket = global % map_nbucket;
int index = map_bucket[ibucket];
while (index > -1) {
if (map_hash[index].global == global) break;
previous = index;
index = map_hash[index].next;
}
if (index > -1) {
map_hash[index].local = local;
return;
}
// take one entry from free list
// add the new global/local pair as entry at end of bucket list
// special logic if this entry is 1st in bucket
index = map_free;
map_free = map_hash[map_free].next;
if (previous == -1) map_bucket[ibucket] = index;
else map_hash[previous].next = index;
map_hash[index].global = global;
map_hash[index].local = local;
map_hash[index].next = -1;
map_nused++;
}
}
/* ----------------------------------------------------------------------
set map style to array or hash based on user request or max atomID
set map_tag_max = max atom ID (may be larger than natoms)
called whenever map_init() called with new total # of atoms
return 1 if map_style changed, else 0
------------------------------------------------------------------------- */
int Atom::map_style_set()
{
if (tag_enable == 0)
error->all(FLERR,"Cannot create an atom map unless atoms have IDs");
// map_tag_max = max ID of any atom that will be in new map
// map_tag_max = -1 if no atoms
tagint max = -1;
for (int i = 0; i < nlocal; i++) max = MAX(max,tag[i]);
MPI_Allreduce(&max,&map_tag_max,1,MPI_LMP_TAGINT,MPI_MAX,world);
// set map_style for new map
// if user-selected, use that setting
// else if map_tag_max > 1M, use hash
// else use array
int map_style_old = map_style;
if (map_user) map_style = map_user;
else if (map_tag_max > 1000000) map_style = 2;
else map_style = 1;
// recreate = 1 if must create new map b/c map_style changed
int recreate = 0;
if (map_style != map_style_old) recreate = 1;
return recreate;
}
/* ----------------------------------------------------------------------
free the array or hash table for global to local mapping
------------------------------------------------------------------------- */
void Atom::map_delete()
{
memory->destroy(sametag);
sametag = NULL;
max_same = 0;
if (map_style == 1) {
memory->destroy(map_array);
map_array = NULL;
} else {
if (map_nhash) {
delete [] map_bucket;
delete [] map_hash;
map_bucket = NULL;
map_hash = NULL;
}
map_nhash = 0;
}
}
/* ----------------------------------------------------------------------
lookup global ID in hash table, return local index
called by map() in atom.h
------------------------------------------------------------------------- */
int Atom::map_find_hash(tagint global)
{
int local = -1;
int index = map_bucket[global % map_nbucket];
while (index > -1) {
if (map_hash[index].global == global) {
local = map_hash[index].local;
break;
}
index = map_hash[index].next;
}
return local;
}
/* ----------------------------------------------------------------------
return next prime larger than n
------------------------------------------------------------------------- */
int Atom::next_prime(int n)
{
int factor;
int nprime = n+1;
if (nprime % 2 == 0) nprime++;
int root = static_cast<int> (sqrt(1.0*n)) + 2;
while (nprime < MAXSMALLINT) {
for (factor = 3; factor < root; factor++)
if (nprime % factor == 0) break;
if (factor == root) return nprime;
nprime += 2;
}
return MAXSMALLINT;
}

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