src/EXTRA-DUMP/dump_xtc.cpp

// clang-format off
/* ----------------------------------------------------------------------
   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
   https://www.lammps.org/, 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.
------------------------------------------------------------------------- */

/* ----------------------------------------------------------------------
   Contributing authors: Naveen Michaud-Agrawal (Johns Hopkins U)
                         open-source XDR routines from
                           Frans van Hoesel (https://www.rug.nl/staff/f.h.j.van.hoesel/)
                           are included in this file
                         Axel Kohlmeyer (Temple U)
                           port to platforms without XDR support
                           added support for unwrapped trajectories
                           support for groups
------------------------------------------------------------------------- */

#include "dump_xtc.h"
#include <cmath>

#include <cstring>
#include <climits>
#include "domain.h"
#include "atom.h"
#include "update.h"
#include "group.h"
#include "output.h"
#include "force.h"
#include "comm.h"
#include "memory.h"
#include "error.h"

using namespace LAMMPS_NS;

#define EPS 1e-5
#define XTC_MAGIC 1995

#define MYMIN(a,b) ((a) < (b) ? (a) : (b))
#define MYMAX(a,b) ((a) > (b) ? (a) : (b))

int xdropen(XDR *, const char *, const char *);
int xdrclose(XDR *);
void xdrfreebuf();
int xdr3dfcoord(XDR *, float *, int *, float *);

/* ---------------------------------------------------------------------- */

DumpXTC::DumpXTC(LAMMPS *lmp, int narg, char **arg) : Dump(lmp, narg, arg),
  coords(nullptr)
{
  if (narg != 5) error->all(FLERR,"Illegal dump xtc command");
  if (binary || compressed || multifile || multiproc)
    error->all(FLERR,"Invalid dump xtc filename");

  size_one = 3;
  sort_flag = 1;
  sortcol = 0;
  format_default = nullptr;
  flush_flag = 0;
  unwrap_flag = 0;
  precision = 1000.0;

  // allocate global array for atom coords

  bigint n = group->count(igroup);
  if (n > static_cast<bigint>(MAXSMALLINT/3/sizeof(float)))
    error->all(FLERR,"Too many atoms for dump xtc");
  natoms = static_cast<int> (n);

  memory->create(coords,3*natoms,"dump:coords");

  // sfactor = conversion of coords to XTC units
  // tfactor = conversion of simulation time to XTC units
  // GROMACS standard is nanometers and picoseconds

  sfactor = 0.1 / force->angstrom;
  tfactor = 0.001 / force->femtosecond;

  // in reduced units we do not scale anything
  if (strcmp(update->unit_style,"lj") == 0) {
    sfactor = tfactor = 1.0;
    if (comm->me == 0)
      error->warning(FLERR,"No automatic unit conversion to XTC file "
                     "format conventions possible for units lj");
  }

  DumpXTC::openfile();
  nevery_save = 0;
  ntotal = 0;
}

/* ---------------------------------------------------------------------- */

DumpXTC::~DumpXTC()
{
  memory->destroy(coords);

  if (me == 0) {
    xdrclose(&xd);
    xdrfreebuf();
  }
}

/* ---------------------------------------------------------------------- */

void DumpXTC::init_style()
{
  if (sort_flag == 0 || sortcol != 0)
    error->all(FLERR,"Dump xtc requires sorting by atom ID");

  // check that flush_flag is not set since dump::write() will use it

  if (flush_flag) error->all(FLERR,"Cannot set dump_modify flush for dump xtc");

  // check that dump frequency has not changed and is not a variable

  int idump;
  for (idump = 0; idump < output->ndump; idump++)
    if (strcmp(id,output->dump[idump]->id) == 0) break;
  if (output->every_dump[idump] == 0)
    error->all(FLERR,"Cannot use variable every setting for dump xtc");

  if (nevery_save == 0) nevery_save = output->every_dump[idump];
  else if (nevery_save != output->every_dump[idump])
    error->all(FLERR,"Cannot change dump_modify every for dump xtc");
}

/* ---------------------------------------------------------------------- */

void DumpXTC::openfile()
{
  // XTC maintains it's own XDR file ptr
  // set fp to a null pointer so parent dump class will not use it

  fp = nullptr;
  if (me == 0)
    if (xdropen(&xd,filename,"w") == 0) error->one(FLERR,"Cannot open dump file");
}

/* ---------------------------------------------------------------------- */

void DumpXTC::write_header(bigint nbig)
{
  if (nbig > MAXSMALLINT) error->all(FLERR,"Too many atoms for dump xtc");
  int n = nbig;
  if (update->ntimestep > MAXSMALLINT)
    error->one(FLERR,"Too big a timestep for dump xtc");
  int ntimestep = update->ntimestep;

  // all procs realloc coords if total count grew

  if (n != natoms) {
    natoms = n;
    memory->destroy(coords);
    memory->create(coords,3*natoms,"dump:coords");
  }

  // only proc 0 writes header

  if (me != 0) return;

  int tmp = XTC_MAGIC;
  xdr_int(&xd,&tmp);
  xdr_int(&xd,&n);
  xdr_int(&xd,&ntimestep);
  float time_value = ntimestep * tfactor * update->dt;
  xdr_float(&xd,&time_value);

  // cell basis vectors
  if (domain->triclinic) {
    float zero = 0.0;
    float xdim = sfactor * (domain->boxhi[0] - domain->boxlo[0]);
    float ydim = sfactor * (domain->boxhi[1] - domain->boxlo[1]);
    float zdim = sfactor * (domain->boxhi[2] - domain->boxlo[2]);
    float xy = sfactor * domain->xy;
    float xz = sfactor * domain->xz;
    float yz = sfactor * domain->yz;

    xdr_float(&xd,&xdim); xdr_float(&xd,&zero); xdr_float(&xd,&zero);
    xdr_float(&xd,&xy  ); xdr_float(&xd,&ydim); xdr_float(&xd,&zero);
    xdr_float(&xd,&xz  ); xdr_float(&xd,&yz  ); xdr_float(&xd,&zdim);
  } else {
    float zero = 0.0;
    float xdim = sfactor * (domain->boxhi[0] - domain->boxlo[0]);
    float ydim = sfactor * (domain->boxhi[1] - domain->boxlo[1]);
    float zdim = sfactor * (domain->boxhi[2] - domain->boxlo[2]);

    xdr_float(&xd,&xdim); xdr_float(&xd,&zero); xdr_float(&xd,&zero);
    xdr_float(&xd,&zero); xdr_float(&xd,&ydim); xdr_float(&xd,&zero);
    xdr_float(&xd,&zero); xdr_float(&xd,&zero); xdr_float(&xd,&zdim);
  }
}

/* ---------------------------------------------------------------------- */

void DumpXTC::pack(tagint *ids)
{
  int m,n;

  tagint *tag = atom->tag;
  double **x = atom->x;
  imageint *image = atom->image;
  int *mask = atom->mask;
  int nlocal = atom->nlocal;

  m = n = 0;
  if (unwrap_flag == 1) {
    double xprd = domain->xprd;
    double yprd = domain->yprd;
    double zprd = domain->zprd;
    double xy = domain->xy;
    double xz = domain->xz;
    double yz = domain->yz;

    for (int i = 0; i < nlocal; i++)
      if (mask[i] & groupbit) {
        int ix = (image[i] & IMGMASK) - IMGMAX;
        int iy = (image[i] >> IMGBITS & IMGMASK) - IMGMAX;
        int iz = (image[i] >> IMG2BITS) - IMGMAX;

        if (domain->triclinic) {
          buf[m++] = sfactor * (x[i][0] + ix * xprd + iy * xy + iz * xz);
          buf[m++] = sfactor * (x[i][1] + iy * yprd + iz * yz);
          buf[m++] = sfactor * (x[i][2] + iz * zprd);
        } else {
          buf[m++] = sfactor * (x[i][0] + ix * xprd);
          buf[m++] = sfactor * (x[i][1] + iy * yprd);
          buf[m++] = sfactor * (x[i][2] + iz * zprd);
        }
        ids[n++] = tag[i];
      }

  } else {
    for (int i = 0; i < nlocal; i++)
      if (mask[i] & groupbit) {
        buf[m++] = sfactor*x[i][0];
        buf[m++] = sfactor*x[i][1];
        buf[m++] = sfactor*x[i][2];
        ids[n++] = tag[i];
      }
  }
}

/* ---------------------------------------------------------------------- */

void DumpXTC::write_data(int n, double *mybuf)
{
  // copy buf atom coords into global array

  int m = 0;
  int k = 3*ntotal;
  for (int i = 0; i < n; i++) {
    coords[k++] = mybuf[m++];
    coords[k++] = mybuf[m++];
    coords[k++] = mybuf[m++];
    ntotal++;
  }

  // if last chunk of atoms in this snapshot, write global arrays to file

  if (ntotal == natoms) {
    write_frame();
    ntotal = 0;
  }
}

/* ---------------------------------------------------------------------- */

int DumpXTC::modify_param(int narg, char **arg)
{
  if (strcmp(arg[0],"unwrap") == 0) {
    if (narg < 2) error->all(FLERR,"Illegal dump_modify command");
    if (strcmp(arg[1],"yes") == 0) unwrap_flag = 1;
    else if (strcmp(arg[1],"no") == 0) unwrap_flag = 0;
    else error->all(FLERR,"Illegal dump_modify command");
    return 2;
  } else if (strcmp(arg[0],"precision") == 0) {
    if (narg < 2) error->all(FLERR,"Illegal dump_modify command");
    precision = utils::numeric(FLERR,arg[1],false,lmp);
    if ((fabs(precision-10.0) > EPS) && (fabs(precision-100.0) > EPS) &&
        (fabs(precision-1000.0) > EPS) && (fabs(precision-10000.0) > EPS) &&
        (fabs(precision-100000.0) > EPS) &&
        (fabs(precision-1000000.0) > EPS))
      error->all(FLERR,"Illegal dump_modify command");
    return 2;
  } else if (strcmp(arg[0],"sfactor") == 0) {
    if (narg < 2) error->all(FLERR,"Illegal dump_modify command");
    sfactor = utils::numeric(FLERR,arg[1],false,lmp);
    if (sfactor <= 0.0)
      error->all(FLERR,"Illegal dump_modify sfactor value (must be > 0.0)");
    return 2;
  } else if (strcmp(arg[0],"tfactor") == 0) {
    if (narg < 2) error->all(FLERR,"Illegal dump_modify command");
    tfactor = utils::numeric(FLERR,arg[1],false,lmp);
    if (tfactor <= 0.0)
      error->all(FLERR,"Illegal dump_modify tfactor value (must be > 0.0)");
    return 2;
  }
  return 0;
}

/* ----------------------------------------------------------------------
   return # of bytes of allocated memory in buf and global coords array
------------------------------------------------------------------------- */

double DumpXTC::memory_usage()
{
  double bytes = Dump::memory_usage();
  bytes += memory->usage(coords,natoms*3);
  return bytes;
}

/* ---------------------------------------------------------------------- */

void DumpXTC::write_frame()
{
  xdr3dfcoord(&xd,coords,&natoms,&precision);
}

// ----------------------------------------------------------------------
// C functions that create GROMOS-compatible XDR files
// open-source
// (c) 1995 Frans van Hoesel, hoesel@chem.rug.nl
// ----------------------------------------------------------------------

/*____________________________________________________________________________
 |
 | Below are the routines to be used by C programmers. Use the 'normal'
 | xdr routines to write integers, floats, etc (see man xdr)
 |
 | int xdropen(XDR *xdrs, const char *filename, const char *type)
 |        This will open the file with the given filename and the
 |        given mode. You should pass it an allocated XDR struct
 |        in xdrs, to be used in all other calls to xdr routines.
 |        Mode is 'w' to create, or update an file, and for all
 |        other values of mode the file is opened for reading.
 |        You need to call xdrclose to flush the output and close
 |        the file.
 |
 |        Note that you should not use xdrstdio_create, which
 |        comes with the standard xdr library.
 |
 | int xdrclose(XDR *xdrs)
 |        Flush the data to the file, and close the file;
 |        You should not use xdr_destroy (which comes standard
 |        with the xdr libraries).
 |
 | int xdr3dfcoord(XDR *xdrs, float *fp, int *size, float *precision)
 |        This is \fInot\fR a standard xdr routine. I named it this
 |        way, because it invites people to use the other xdr
 |        routines.
 |
 |        (c) 1995 Frans van Hoesel, hoesel@chem.rug.nl
*/

#define MAXID 20
static FILE *xdrfiles[MAXID];
static XDR *xdridptr[MAXID];
static char xdrmodes[MAXID];
static int *ip = nullptr;
static int *buf = nullptr;

/*___________________________________________________________________________
 |
 | what follows are the C routines for opening, closing xdr streams
 | and the routine to read/write compressed coordinates together
 | with some routines to assist in this task (those are marked
 | static and cannot be called from user programs)
*/
#define MAXABS INT_MAX-2

#ifndef SQR
#define SQR(x) ((x)*(x))
#endif
static int magicints[] = {
  0, 0, 0, 0, 0, 0, 0, 0, 0,
  8, 10, 12, 16, 20, 25, 32, 40, 50, 64,
  80, 101, 128, 161, 203, 256, 322, 406, 512, 645,
  812, 1024, 1290, 1625, 2048, 2580, 3250, 4096, 5060, 6501,
  8192, 10321, 13003, 16384, 20642, 26007, 32768, 41285, 52015, 65536,
  82570, 104031, 131072, 165140, 208063, 262144, 330280, 416127,
  524287, 660561,
  832255, 1048576, 1321122, 1664510, 2097152, 2642245, 3329021,
  4194304, 5284491, 6658042,
  8388607, 10568983, 13316085, 16777216 };

#define FIRSTIDX 9
/* note that magicints[FIRSTIDX-1] == 0 */
#define LASTIDX (sizeof(magicints) / sizeof(int) - 1 )

/*__________________________________________________________________________
 |
 | xdropen - open xdr file
 |
 | This versions differs from xdrstdio_create, because I need to know
 | the state of the file (read or write) so I can use xdr3dfcoord
 | in eigther read or write mode, and the file descriptor
 | so I can close the file (something xdr_destroy doesn't do).
 |
*/

int xdropen(XDR *xdrs, const char *filename, const char *type)
{
  static int init_done = 0;
  enum xdr_op lmode;
  int xdrid;

  if (init_done == 0) {
    for (xdrid = 1; xdrid < MAXID; xdrid++) {
      xdridptr[xdrid] = nullptr;
    }
    init_done = 1;
  }
  xdrid = 1;
  while (xdrid < MAXID && xdridptr[xdrid] != nullptr) {
    xdrid++;
  }
  if (xdrid == MAXID) {
    return 0;
  }
  if (*type == 'w' || *type == 'W') {
    type = (char *) "w+";
    lmode = XDR_ENCODE;
  } else {
    type = (char *) "r";
    lmode = XDR_DECODE;
  }
  xdrfiles[xdrid] = fopen(filename, type);
  if (xdrfiles[xdrid] == nullptr) {
    xdrs = nullptr;
    return 0;
  }
  xdrmodes[xdrid] = *type;

  /* next test isn't useful in the case of C language
   * but is used for the Fortran interface
   * (C users are expected to pass the address of an already allocated
   * XDR staructure)
   */
  if (xdrs == nullptr) {
    xdridptr[xdrid] = (XDR *) malloc(sizeof(XDR));
    xdrstdio_create(xdridptr[xdrid], xdrfiles[xdrid], lmode);
  } else {
    xdridptr[xdrid] = xdrs;
    xdrstdio_create(xdrs, xdrfiles[xdrid], lmode);
  }
  return xdrid;
}

/*_________________________________________________________________________
 |
 | xdrclose - close a xdr file
 |
 | This will flush the xdr buffers, and destroy the xdr stream.
 | It also closes the associated file descriptor (this is *not*
 | done by xdr_destroy).
 |
*/

int xdrclose(XDR *xdrs)
{
  int xdrid;

  if (xdrs == nullptr) {
    fprintf(stderr, "xdrclose: passed a NULL pointer\n");
    exit(1);
  }
  for (xdrid = 1; xdrid < MAXID; xdrid++) {
    if (xdridptr[xdrid] == xdrs) {

      xdr_destroy(xdrs);
      fclose(xdrfiles[xdrid]);
      xdridptr[xdrid] = nullptr;
      return 1;
    }
  }
  fprintf(stderr, "xdrclose: no such open xdr file\n");
  exit(1);
  return 1;
}

/*_________________________________________________________________________
 |
 | xdrfreebuf - free the buffers used by xdr3dfcoord
 |
*/
void xdrfreebuf()
{
  if (ip) free(ip);
  if (buf) free(buf);
  ip = nullptr;
  buf = nullptr;
}


/*____________________________________________________________________________
 |
 | sendbits - encode num into buf using the specified number of bits
 |
 | This routines appends the value of num to the bits already present in
 | the array buf. You need to give it the number of bits to use and you
 | better make sure that this number of bits is enough to hold the value
 | Also num must be positive.
 |
*/

static void sendbits(int buf[], int num_of_bits, int num)
{
  unsigned int cnt, lastbyte;
  int lastbits;
  unsigned char * cbuf;

  cbuf = ((unsigned char *)buf) + 3 * sizeof(*buf);
  cnt = (unsigned int) buf[0];
  lastbits = buf[1];
  lastbyte =(unsigned int) buf[2];
  while (num_of_bits >= 8) {
    lastbyte = (lastbyte << 8) | ((num >> (num_of_bits -8)) /* & 0xff*/);
    cbuf[cnt++] = lastbyte >> lastbits;
    num_of_bits -= 8;
  }
  if (num_of_bits > 0) {
    lastbyte = (lastbyte << num_of_bits) | num;
    lastbits += num_of_bits;
    if (lastbits >= 8) {
      lastbits -= 8;
      cbuf[cnt++] = lastbyte >> lastbits;
    }
  }
  buf[0] = cnt;
  buf[1] = lastbits;
  buf[2] = lastbyte;
  if (lastbits>0) {
    cbuf[cnt] = lastbyte << (8 - lastbits);
  }
}

/*_________________________________________________________________________
 |
 | sizeofint - calculate bitsize of an integer
 |
 | return the number of bits needed to store an integer with given max size
 |
*/

static int sizeofint(const int size)
{
  unsigned int num = 1;
  int num_of_bits = 0;

  while (size >= (int) num && num_of_bits < 32) {
    num_of_bits++;
    num <<= 1;
  }
  return num_of_bits;
}

/*___________________________________________________________________________
 |
 | sizeofints - calculate 'bitsize' of compressed ints
 |
 | given the number of small unsigned integers and the maximum value
 | return the number of bits needed to read or write them with the
 | routines receiveints and sendints. You need this parameter when
 | calling these routines. Note that for many calls I can use
 | the variable 'smallidx' which is exactly the number of bits, and
 | So I don't need to call 'sizeofints for those calls.
*/

static int sizeofints( const int num_of_ints, unsigned int sizes[])
{
  int i, num;
  unsigned int num_of_bytes, num_of_bits, bytes[32], bytecnt, tmp;
  num_of_bytes = 1;
  bytes[0] = 1;
  num_of_bits = 0;
  for (i=0; i < num_of_ints; i++) {
    tmp = 0;
    for (bytecnt = 0; bytecnt < num_of_bytes; bytecnt++) {
      tmp = bytes[bytecnt] * sizes[i] + tmp;
      bytes[bytecnt] = tmp & 0xff;
      tmp >>= 8;
    }
    while (tmp != 0) {
      bytes[bytecnt++] = tmp & 0xff;
      tmp >>= 8;
    }
    num_of_bytes = bytecnt;
  }
  num = 1;
  num_of_bytes--;
  while ((int)bytes[num_of_bytes] >= num) {
    num_of_bits++;
    num *= 2;
  }
  return num_of_bits + num_of_bytes * 8;
}

/*____________________________________________________________________________
 |
 | sendints - send a small set of small integers in compressed
 |
 | this routine is used internally by xdr3dfcoord, to send a set of
 | small integers to the buffer.
 | Multiplication with fixed (specified maximum ) sizes is used to get
 | to one big, multibyte integer. Although the routine could be
 | modified to handle sizes bigger than 16777216, or more than just
 | a few integers, this is not done, because the gain in compression
 | isn't worth the effort. Note that overflowing the multiplication
 | or the byte buffer (32 bytes) is unchecked and causes bad results.
 |
 */

static void sendints(int buf[], const int num_of_ints, const int num_of_bits,
                     unsigned int sizes[], unsigned int nums[])
{
  int i;
  unsigned int bytes[32], num_of_bytes, bytecnt, tmp;

  tmp = nums[0];
  num_of_bytes = 0;
  do {
    bytes[num_of_bytes++] = tmp & 0xff;
    tmp >>= 8;
  } while (tmp != 0);

  for (i = 1; i < num_of_ints; i++) {
    if (nums[i] >= sizes[i]) {
      fprintf(stderr,"major breakdown in sendints num %d doesn't "
              "match size %d\n", nums[i], sizes[i]);
      exit(1);
    }
    /* use one step multiply */
    tmp = nums[i];
    for (bytecnt = 0; bytecnt < num_of_bytes; bytecnt++) {
      tmp = bytes[bytecnt] * sizes[i] + tmp;
      bytes[bytecnt] = tmp & 0xff;
      tmp >>= 8;
    }
    while (tmp != 0) {
      bytes[bytecnt++] = tmp & 0xff;
      tmp >>= 8;
    }
    num_of_bytes = bytecnt;
  }
  if (num_of_bits >= (int)num_of_bytes * 8) {
    for (i = 0; i < (int)num_of_bytes; i++) {
      sendbits(buf, 8, bytes[i]);
    }
    sendbits(buf, num_of_bits - num_of_bytes * 8, 0);
  } else {
    for (i = 0; i < (int)num_of_bytes-1; i++) {
      sendbits(buf, 8, bytes[i]);
    }
    sendbits(buf, num_of_bits- (num_of_bytes -1) * 8, bytes[i]);
  }
}

/*___________________________________________________________________________
 |
 | receivebits - decode number from buf using specified number of bits
 |
 | extract the number of bits from the array buf and construct an integer
 | from it. Return that value.
 |
*/

static int receivebits(int buf[], int num_of_bits)
{
  int cnt, num;
  unsigned int lastbits, lastbyte;
  unsigned char * cbuf;
  int mask = (1 << num_of_bits) -1;

  cbuf = ((unsigned char *)buf) + 3 * sizeof(*buf);
  cnt = buf[0];
  lastbits = (unsigned int) buf[1];
  lastbyte = (unsigned int) buf[2];

  num = 0;
  while (num_of_bits >= 8) {
    lastbyte = ( lastbyte << 8 ) | cbuf[cnt++];
    num |=  (lastbyte >> lastbits) << (num_of_bits - 8);
    num_of_bits -=8;
  }
  if (num_of_bits > 0) {
    if ((int)lastbits < num_of_bits) {
      lastbits += 8;
      lastbyte = (lastbyte << 8) | cbuf[cnt++];
    }
    lastbits -= num_of_bits;
    num |= (lastbyte >> lastbits) & ((1 << num_of_bits) -1);
  }
  num &= mask;
  buf[0] = cnt;
  buf[1] = lastbits;
  buf[2] = lastbyte;
  return num;
}

/*____________________________________________________________________________
 |
 | receiveints - decode 'small' integers from the buf array
 |
 | this routine is the inverse from sendints() and decodes the small integers
 | written to buf by calculating the remainder and doing divisions with
 | the given sizes[]. You need to specify the total number of bits to be
 | used from buf in num_of_bits.
 |
*/

static void receiveints(int buf[], const int num_of_ints, int num_of_bits,
                        unsigned int sizes[], int nums[])
{
  int bytes[32];
  int i, j, num_of_bytes, p, num;

  bytes[1] = bytes[2] = bytes[3] = 0;
  num_of_bytes = 0;
  while (num_of_bits > 8) {
    bytes[num_of_bytes++] = receivebits(buf, 8);
    num_of_bits -= 8;
  }
  if (num_of_bits > 0) {
    bytes[num_of_bytes++] = receivebits(buf, num_of_bits);
  }
  for (i = num_of_ints-1; i > 0; i--) {
    num = 0;
    for (j = num_of_bytes-1; j >=0; j--) {
      num = (num << 8) | bytes[j];
      p = num / sizes[i];
      bytes[j] = p;
      num = num - p * sizes[i];
    }
    nums[i] = num;
  }
  nums[0] = bytes[0] | (bytes[1] << 8) | (bytes[2] << 16) | (bytes[3] << 24);
}

/*____________________________________________________________________________
 |
 | xdr3dfcoord - read or write compressed 3d coordinates to xdr file.
 |
 | this routine reads or writes (depending on how you opened the file with
 | xdropen() ) a large number of 3d coordinates (stored in *fp).
 | The number of coordinates triplets to write is given by *size. On
 | read this number may be zero, in which case it reads as many as were written
 | or it may specify the number if triplets to read (which should match the
 | number written).
 | Compression is achieved by first converting all floating numbers to integer
 | using multiplication by *precision and rounding to the nearest integer.
 | Then the minimum and maximum value are calculated to determine the range.
 | The limited range of integers so found, is used to compress the coordinates.
 | In addition the differences between successive coordinates is calculated.
 | If the difference happens to be 'small' then only the difference is saved,
 | compressing the data even more. The notion of 'small' is changed dynamically
 | and is enlarged or reduced whenever needed or possible.
 | Extra compression is achieved in the case of GROMOS and coordinates of
 | water molecules. GROMOS first writes out the Oxygen position, followed by
 | the two hydrogens. In order to make the differences smaller (and thereby
 | compression the data better) the order is changed into first one hydrogen
 | then the oxygen, followed by the other hydrogen. This is rather special, but
 | it shouldn't harm in the general case.
 |
 */

int xdr3dfcoord(XDR *xdrs, float *fp, int *size, float *precision)
{
  static int oldsize;

  int minint[3], maxint[3], mindiff, *lip, diff;
  int lint1, lint2, lint3, oldlint1, oldlint2, oldlint3, smallidx;
  int minidx, maxidx;
  unsigned sizeint[3], sizesmall[3], bitsizeint[3], size3, *luip;
  int flag, k;
  int small, smaller, larger, i, is_small, is_smaller, run, prevrun;
  float *lfp, lf;
  int tmp, *thiscoord,  prevcoord[3];
  unsigned int tmpcoord[30];

  int bufsize, xdrid, lsize;
  unsigned int bitsize;
  float inv_precision;
  int errval = 1;

  /* find out if xdrs is opened for reading or for writing */
  xdrid = 0;
  while (xdridptr[xdrid] != xdrs) {
    xdrid++;
    if (xdrid >= MAXID) {
      fprintf(stderr, "xdr error. no open xdr stream\n");
      exit (1);
    }
  }
  if (xdrmodes[xdrid] == 'w') {

    /* xdrs is open for writing */

    if (xdr_int(xdrs, size) == 0)
      return 0;
    size3 = *size * 3;
    /* when the number of coordinates is small, don't try to compress; just
     * write them as floats using xdr_vector
     */
    if (*size <= 9) {
      return (xdr_vector(xdrs, (char *) fp, size3, sizeof(*fp),
                         (xdrproc_t)xdr_float));
    }

    xdr_float(xdrs, precision);
    if (ip == nullptr) {
      ip = (int *) malloc(size3 * sizeof(*ip));
      if (ip == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      bufsize = (int) (size3 * 1.2);
      buf = (int *) malloc(bufsize * sizeof(*buf));
      if (buf == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      oldsize = *size;
    } else if (*size > oldsize) {
      ip = (int *) realloc(ip, size3 * sizeof(*ip));
      if (ip == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      bufsize = (int) (size3 * 1.2);
      buf = (int *) realloc(buf, bufsize * sizeof(*buf));
      if (buf == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      oldsize = *size;
    }
    /* buf[0-2] are special and do not contain actual data */
    buf[0] = buf[1] = buf[2] = 0;
    minint[0] = minint[1] = minint[2] = INT_MAX;
    maxint[0] = maxint[1] = maxint[2] = INT_MIN;
    prevrun = -1;
    lfp = fp;
    lip = ip;
    mindiff = INT_MAX;
    oldlint1 = oldlint2 = oldlint3 = 0;
    while (lfp < fp + size3) {
      /* find nearest integer */
      if (*lfp >= 0.0)
        lf = *lfp * *precision + 0.5;
      else
        lf = *lfp * *precision - 0.5;
      if (fabs(lf) > MAXABS) {
        /* scaling would cause overflow */
        errval = 0;
      }
      lint1 = (int) lf;
      if (lint1 < minint[0]) minint[0] = lint1;
      if (lint1 > maxint[0]) maxint[0] = lint1;
      *lip++ = lint1;
      lfp++;
      if (*lfp >= 0.0)
        lf = *lfp * *precision + 0.5;
      else
        lf = *lfp * *precision - 0.5;
      if (fabs(lf) > MAXABS) {
        /* scaling would cause overflow */
        errval = 0;
      }
      lint2 = (int) lf;
      if (lint2 < minint[1]) minint[1] = lint2;
      if (lint2 > maxint[1]) maxint[1] = lint2;
      *lip++ = lint2;
      lfp++;
      if (*lfp >= 0.0)
        lf = *lfp * *precision + 0.5;
      else
        lf = *lfp * *precision - 0.5;
      if (fabs(lf) > MAXABS) {
        /* scaling would cause overflow */
        errval = 0;
      }
      lint3 = (int) lf;
      if (lint3 < minint[2]) minint[2] = lint3;
      if (lint3 > maxint[2]) maxint[2] = lint3;
      *lip++ = lint3;
      lfp++;
      diff = abs(oldlint1-lint1)+abs(oldlint2-lint2)+abs(oldlint3-lint3);
      if (diff < mindiff && lfp > fp + 3)
        mindiff = diff;
      oldlint1 = lint1;
      oldlint2 = lint2;
      oldlint3 = lint3;
    }
    xdr_int(xdrs, &(minint[0]));
    xdr_int(xdrs, &(minint[1]));
    xdr_int(xdrs, &(minint[2]));

    xdr_int(xdrs, &(maxint[0]));
    xdr_int(xdrs, &(maxint[1]));
    xdr_int(xdrs, &(maxint[2]));

    if ((float)maxint[0] - (float)minint[0] >= MAXABS ||
        (float)maxint[1] - (float)minint[1] >= MAXABS ||
        (float)maxint[2] - (float)minint[2] >= MAXABS) {
      /* turning value in unsigned by subtracting minint
       * would cause overflow
       */
      errval = 0;
    }
    sizeint[0] = maxint[0] - minint[0]+1;
    sizeint[1] = maxint[1] - minint[1]+1;
    sizeint[2] = maxint[2] - minint[2]+1;

    /* check if one of the sizes is to big to be multiplied */
    if ((sizeint[0] | sizeint[1] | sizeint[2] ) > 0xffffff) {
      bitsizeint[0] = sizeofint(sizeint[0]);
      bitsizeint[1] = sizeofint(sizeint[1]);
      bitsizeint[2] = sizeofint(sizeint[2]);
      bitsize = 0; /* flag the use of large sizes */
    } else {
      bitsize = sizeofints(3, sizeint);
    }
    lip = ip;
    luip = (unsigned int *) ip;
    smallidx = FIRSTIDX;
    while (smallidx < (int)LASTIDX && magicints[smallidx] < mindiff) {
      smallidx++;
    }
    xdr_int(xdrs, &smallidx);
    maxidx = MYMIN((int)LASTIDX, smallidx + 8) ;
    minidx = maxidx - 8; /* often this equal smallidx */
    smaller = magicints[MYMAX(FIRSTIDX, smallidx-1)] / 2;
    small = magicints[smallidx] / 2;
    sizesmall[0] = sizesmall[1] = sizesmall[2] = magicints[smallidx];
    larger = magicints[maxidx] / 2;
    i = 0;
    while (i < *size) {
      is_small = 0;
      thiscoord = (int *)(luip) + i * 3;
      if (smallidx < maxidx && i >= 1 &&
          abs(thiscoord[0] - prevcoord[0]) < larger &&
          abs(thiscoord[1] - prevcoord[1]) < larger &&
          abs(thiscoord[2] - prevcoord[2]) < larger) {
        is_smaller = 1;
      } else if (smallidx > minidx) {
        is_smaller = -1;
      } else {
        is_smaller = 0;
      }
      if (i + 1 < *size) {
        if (abs(thiscoord[0] - thiscoord[3]) < small &&
            abs(thiscoord[1] - thiscoord[4]) < small &&
            abs(thiscoord[2] - thiscoord[5]) < small) {
          /* interchange first with second atom for better
           * compression of water molecules
           */
          tmp = thiscoord[0]; thiscoord[0] = thiscoord[3];
          thiscoord[3] = tmp;
          tmp = thiscoord[1]; thiscoord[1] = thiscoord[4];
          thiscoord[4] = tmp;
          tmp = thiscoord[2]; thiscoord[2] = thiscoord[5];
          thiscoord[5] = tmp;
          is_small = 1;
        }

      }
      tmpcoord[0] = thiscoord[0] - minint[0];
      tmpcoord[1] = thiscoord[1] - minint[1];
      tmpcoord[2] = thiscoord[2] - minint[2];
      if (bitsize == 0) {
        sendbits(buf, bitsizeint[0], tmpcoord[0]);
        sendbits(buf, bitsizeint[1], tmpcoord[1]);
        sendbits(buf, bitsizeint[2], tmpcoord[2]);
      } else {
        sendints(buf, 3, bitsize, sizeint, tmpcoord);
      }
      prevcoord[0] = thiscoord[0];
      prevcoord[1] = thiscoord[1];
      prevcoord[2] = thiscoord[2];
      thiscoord = thiscoord + 3;
      i++;

      run = 0;
      if (is_small == 0 && is_smaller == -1)
        is_smaller = 0;
      while (is_small && run < 8*3) {
        if (is_smaller == -1 && (SQR(thiscoord[0] - prevcoord[0]) +
                                 SQR(thiscoord[1] - prevcoord[1]) +
                                 SQR(thiscoord[2] - prevcoord[2]) >=
                                 smaller * smaller)) {
          is_smaller = 0;
        }

        tmpcoord[run++] = thiscoord[0] - prevcoord[0] + small;
        tmpcoord[run++] = thiscoord[1] - prevcoord[1] + small;
        tmpcoord[run++] = thiscoord[2] - prevcoord[2] + small;

        prevcoord[0] = thiscoord[0];
        prevcoord[1] = thiscoord[1];
        prevcoord[2] = thiscoord[2];

        i++;
        thiscoord = thiscoord + 3;
        is_small = 0;
        if (i < *size &&
            abs(thiscoord[0] - prevcoord[0]) < small &&
            abs(thiscoord[1] - prevcoord[1]) < small &&
            abs(thiscoord[2] - prevcoord[2]) < small) {
          is_small = 1;
        }
      }
      if (run != prevrun || is_smaller != 0) {
        prevrun = run;
        sendbits(buf, 1, 1); /* flag the change in run-length */
        sendbits(buf, 5, run+is_smaller+1);
      } else {
        sendbits(buf, 1, 0); /* flag the fact that runlength did not change */
      }
      for (k=0; k < run; k+=3) {
        sendints(buf, 3, smallidx, sizesmall, &tmpcoord[k]);
      }
      if (is_smaller != 0) {
        smallidx += is_smaller;
        if (is_smaller < 0) {
          small = smaller;
          smaller = magicints[smallidx-1] / 2;
        } else {
          smaller = small;
          small = magicints[smallidx] / 2;
        }
        sizesmall[0] = sizesmall[1] = sizesmall[2] = magicints[smallidx];
      }
    }
    if (buf[1] != 0) buf[0]++;;
    xdr_int(xdrs, &(buf[0])); /* buf[0] holds the length in bytes */
    return errval * (xdr_opaque(xdrs, (caddr_t)&(buf[3]), (u_int)buf[0]));
  } else {

    /* xdrs is open for reading */

    if (xdr_int(xdrs, &lsize) == 0)
      return 0;
    if (*size != 0 && lsize != *size) {
      fprintf(stderr, "wrong number of coordinates in xdr3dfcoor; "
              "%d arg vs %d in file", *size, lsize);
    }
    *size = lsize;
    size3 = *size * 3;
    if (*size <= 9) {
      return (xdr_vector(xdrs, (char *) fp, size3, sizeof(*fp),
                         (xdrproc_t)xdr_float));
    }
    xdr_float(xdrs, precision);
    if (ip == nullptr) {
      ip = (int *) malloc(size3 * sizeof(*ip));
      if (ip == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      bufsize = (int) (size3 * 1.2);
      buf = (int *) malloc(bufsize * sizeof(*buf));
      if (buf == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      oldsize = *size;
    } else if (*size > oldsize) {
      ip = (int *)realloc(ip, size3 * sizeof(*ip));
      if (ip == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      bufsize = (int) (size3 * 1.2);
      buf = (int *)realloc(buf, bufsize * sizeof(*buf));
      if (buf == nullptr) {
        fprintf(stderr,"malloc failed\n");
        exit(1);
      }
      oldsize = *size;
    }
    buf[0] = buf[1] = buf[2] = 0;

    xdr_int(xdrs, &(minint[0]));
    xdr_int(xdrs, &(minint[1]));
    xdr_int(xdrs, &(minint[2]));

    xdr_int(xdrs, &(maxint[0]));
    xdr_int(xdrs, &(maxint[1]));
    xdr_int(xdrs, &(maxint[2]));

    sizeint[0] = maxint[0] - minint[0]+1;
    sizeint[1] = maxint[1] - minint[1]+1;
    sizeint[2] = maxint[2] - minint[2]+1;

    /* check if one of the sizes is to big to be multiplied */
    if ((sizeint[0] | sizeint[1] | sizeint[2] ) > 0xffffff) {
      bitsizeint[0] = sizeofint(sizeint[0]);
      bitsizeint[1] = sizeofint(sizeint[1]);
      bitsizeint[2] = sizeofint(sizeint[2]);
      bitsize = 0; /* flag the use of large sizes */
    } else {
      bitsize = sizeofints(3, sizeint);
    }

    xdr_int(xdrs, &smallidx);
    maxidx = MYMIN((int)LASTIDX, smallidx + 8) ;
    minidx = maxidx - 8; /* often this equal smallidx */
    smaller = magicints[MYMAX(FIRSTIDX, smallidx-1)] / 2;
    small = magicints[smallidx] / 2;
    sizesmall[0] = sizesmall[1] = sizesmall[2] = magicints[smallidx] ;
    larger = magicints[maxidx];

    /* buf[0] holds the length in bytes */

    if (xdr_int(xdrs, &(buf[0])) == 0)
      return 0;
    if (xdr_opaque(xdrs, (caddr_t)&(buf[3]), (u_int)buf[0]) == 0)
      return 0;
    buf[0] = buf[1] = buf[2] = 0;

    lfp = fp;
    inv_precision = 1.0 / * precision;
    run = 0;
    i = 0;
    lip = ip;
    while (i < lsize) {
      thiscoord = (int *)(lip) + i * 3;

      if (bitsize == 0) {
        thiscoord[0] = receivebits(buf, bitsizeint[0]);
        thiscoord[1] = receivebits(buf, bitsizeint[1]);
        thiscoord[2] = receivebits(buf, bitsizeint[2]);
      } else {
        receiveints(buf, 3, bitsize, sizeint, thiscoord);
      }

      i++;
      thiscoord[0] += minint[0];
      thiscoord[1] += minint[1];
      thiscoord[2] += minint[2];

      prevcoord[0] = thiscoord[0];
      prevcoord[1] = thiscoord[1];
      prevcoord[2] = thiscoord[2];


      flag = receivebits(buf, 1);
      is_smaller = 0;
      if (flag == 1) {
        run = receivebits(buf, 5);
        is_smaller = run % 3;
        run -= is_smaller;
        is_smaller--;
      }
      if (run > 0) {
        thiscoord += 3;
        for (k = 0; k < run; k+=3) {
          receiveints(buf, 3, smallidx, sizesmall, thiscoord);
          i++;
          thiscoord[0] += prevcoord[0] - small;
          thiscoord[1] += prevcoord[1] - small;
          thiscoord[2] += prevcoord[2] - small;
          if (k == 0) {
            /* interchange first with second atom for better
             * compression of water molecules
             */
            tmp = thiscoord[0]; thiscoord[0] = prevcoord[0];
            prevcoord[0] = tmp;
            tmp = thiscoord[1]; thiscoord[1] = prevcoord[1];
            prevcoord[1] = tmp;
            tmp = thiscoord[2]; thiscoord[2] = prevcoord[2];
            prevcoord[2] = tmp;
            *lfp++ = prevcoord[0] * inv_precision;
            *lfp++ = prevcoord[1] * inv_precision;
            *lfp++ = prevcoord[2] * inv_precision;
          } else {
            prevcoord[0] = thiscoord[0];
            prevcoord[1] = thiscoord[1];
            prevcoord[2] = thiscoord[2];
          }
          *lfp++ = thiscoord[0] * inv_precision;
          *lfp++ = thiscoord[1] * inv_precision;
          *lfp++ = thiscoord[2] * inv_precision;
        }
      } else {
        *lfp++ = thiscoord[0] * inv_precision;
        *lfp++ = thiscoord[1] * inv_precision;
        *lfp++ = thiscoord[2] * inv_precision;
      }
      smallidx += is_smaller;
      if (is_smaller < 0) {
        small = smaller;
        if (smallidx > FIRSTIDX) {
          smaller = magicints[smallidx - 1] /2;
        } else {
          smaller = 0;
        }
      } else if (is_smaller > 0) {
        smaller = small;
        small = magicints[smallidx] / 2;
      }
      sizesmall[0] = sizesmall[1] = sizesmall[2] = magicints[smallidx] ;
    }
  }
  return 1;
}