Improve libdcd cython

package/CHANGELOG

@@ -34,6 +34,7 @@ Fixes
     (e.g. bonds, angles) (PR #3779).
 
 Enhancements
+  * Improve C content of libdcd Cython (Issue #3882, PR #3888)
   * The timeseries method for exporting coordinates from multiple frames to a
     NumPy array was added to ProtoReader (PR #3890)
   * MDAnalysis now officially supports py3.11 (Issue #3878)
@@ -70,6 +71,8 @@ Changes
   * adding element attribute to TXYZParser if all atom names are valid element symbols (PR #3826)
 
 Deprecations
+  * Add deprecation warning for `timestep` copying in DCDReader
+    (Issue #3889, PR #3888)
   * Add deprecation warning for inclusive stop indexing in
     MemoryReader.timeseries (#PR 3894)
 

package/MDAnalysis/coordinates/DCD.py

@@ -96,6 +96,14 @@ class DCDReader(base.ReaderBase):
     degrees then it is assumed it is a new-style CHARMM unitcell (at least
     since c36b2) in which box vectors were recorded.
 
+    .. deprecated:: 2.4.0
+        DCDReader currently makes independent timesteps
+        by copying the :class:`Timestep` associated with the reader.
+        Other readers update the :class:`Timestep` inplace meaning all
+        references to the :class:`Timestep` contain the same data. The unique
+        independent :class:`Timestep` behaviour of the DCDReader is deprecated
+        will be changed in 3.0 to be the same as other readers
+
     .. warning::
         The DCD format is not well defined. Check your unit cell
         dimensions carefully, especially when using triclinic boxes.
@@ -154,6 +162,11 @@ def __init__(self, filename, convert_units=True, dt=None, **kwargs):
         self.ts = self._frame_to_ts(frame, self.ts)
         # these should only be initialized once
         self.ts.dt = dt
+        warnings.warn("DCDReader currently makes independent timesteps"
+                      " by copying self.ts while other readers update"
+                      " self.ts inplace. This behaviour will be changed in"
+                      " 3.0 to be the same as other readers",
+                       category=DeprecationWarning)
 
     @staticmethod
     def parse_n_atoms(filename, **kwargs):
@@ -188,12 +201,11 @@ def _read_next_timestep(self, ts=None):
         if self._frame == self.n_frames - 1:
             raise IOError('trying to go over trajectory limit')
         if ts is None:
-            # use a copy to avoid that ts always points to the same reference
-            # removing this breaks lammps reader
+            #TODO remove copying the ts in 3.0 
             ts = self.ts.copy()
         frame = self._file.read()
         self._frame += 1
-        ts = self._frame_to_ts(frame, ts)
+        self._frame_to_ts(frame, ts)
         self.ts = ts
         return ts
 

package/MDAnalysis/lib/formats/libdcd.pxd

@@ -0,0 +1,155 @@
+# -*- Mode: python; tab-width: 4; indent-tabs-mode:nil; coding:utf-8 -*-
+# vim: tabstop=4 expandtab shiftwidth=4 softtabstop=4 fileencoding=utf-8
+#
+# MDAnalysis --- https://www.mdanalysis.org
+# Copyright (c) 2006-2017 The MDAnalysis Development Team and contributors
+# (see the file AUTHORS for the full list of names)
+#
+# Released under the GNU Public Licence, v2 or any higher version
+#
+# Please cite your use of MDAnalysis in published work:
+#
+# R. J. Gowers, M. Linke, J. Barnoud, T. J. E. Reddy, M. N. Melo, S. L. Seyler,
+# D. L. Dotson, J. Domanski, S. Buchoux, I. M. Kenney, and O. Beckstein.
+# MDAnalysis: A Python package for the rapid analysis of molecular dynamics
+# simulations. In S. Benthall and S. Rostrup editors, Proceedings of the 15th
+# Python in Science Conference, pages 102-109, Austin, TX, 2016. SciPy.
+# doi: 10.25080/majora-629e541a-00e
+#
+# N. Michaud-Agrawal, E. J. Denning, T. B. Woolf, and O. Beckstein.
+# MDAnalysis: A Toolkit for the Analysis of Molecular Dynamics Simulations.
+# J. Comput. Chem. 32 (2011), 2319--2327, doi:10.1002/jcc.21787
+#
+
+
+from libc.stdlib cimport free
+from libc.stdint cimport uintptr_t
+from libc.stdio cimport SEEK_SET, SEEK_CUR, SEEK_END
+import cython
+
+cimport numpy as np
+
+np.import_array()
+
+
+# Tell cython about the off_t type. It doesn't need to match exactly what is
+# defined since we don't expose it to python but the cython compiler needs to
+# know about it.
+cdef extern from 'sys/types.h':
+    ctypedef int off_t
+
+ctypedef int fio_fd
+ctypedef off_t fio_size_t
+
+cdef extern from 'include/fastio.h':
+    int fio_open(const char * filename, int mode, fio_fd * fd)
+    int fio_fclose(fio_fd fd)
+    fio_size_t fio_ftell(fio_fd fd)
+    fio_size_t fio_fseek(fio_fd fd, fio_size_t offset, int whence)
+
+cdef extern from 'include/readdcd.h':
+    int read_dcdheader(fio_fd fd, int * natoms, int * nsets, int * istart,
+                       int * nsavc, double * delta, int * nfixed, int ** freeind,
+                       float ** fixedcoords, int * reverse_endian, int * charmm,
+                       char ** remarks, int * len_remarks)
+    void close_dcd_read(int * freeind, float * fixedcoords)
+    int read_dcdstep(fio_fd fd, int natoms, float * X, float * Y, float * Z,
+                     double * unitcell, int num_fixed,
+                     int first, int * indexes, float * fixedcoords,
+                     int reverse_endian, int charmm)
+    int read_dcdsubset(fio_fd fd, int natoms, int lowerb, int upperb,
+                       float * X, float * Y, float * Z,
+                       double * unitcell, int num_fixed,
+                       int first, int * indexes, float * fixedcoords,
+                       int reverse_endian, int charmm)
+    int write_dcdheader(fio_fd fd, const char * remarks, int natoms,
+                        int istart, int nsavc, double delta, int with_unitcell,
+                        int charmm)
+    int write_dcdstep(fio_fd fd, int curframe, int curstep,
+                      int natoms, const float * x, const float * y, const float * z,
+                      const double * unitcell, int charmm)
+
+cdef class DCDFile:
+    """DCDFile(fname, mode='r')
+
+    File like wrapper for DCD files
+
+    This class can be similar to the normal file objects in python. The read()
+    function will return a frame and all information in it instead of a single
+    line. Additionally the context-manager protocol is supported as well.
+    """
+    # DCD file pointer
+    cdef fio_fd fp
+    # File name
+    cdef readonly fname
+    # Starting timestep of dcd file
+    cdef int istart
+    # Timesteps between dcd saves
+    cdef int nsavc
+    # Trajectory timestep
+    cdef double delta
+    # Number of atoms
+    cdef int natoms
+    # Number of fixed atoms
+    cdef int nfixed
+    # Free indices
+    cdef int * freeind
+    # Fixed coordinates
+    cdef float * fixedcoords
+    # Are we reverse endian?
+    cdef int reverse_endian
+    # Is the DCD file CHARMM style
+    cdef int charmm
+    # Is the file periodic
+    cdef readonly int is_periodic
+    # String data in the file
+    cdef remarks
+    # File mode
+    cdef str mode
+    # Number of dimensions in 
+    cdef readonly int ndims
+    # The number of frames
+    cdef readonly int n_frames
+    # Flag to indicate if header has been read
+    cdef bint b_read_header
+    # The current DCD frame
+    cdef int current_frame
+    # size of the first DCD frame
+    cdef readonly int _firstframesize
+    # Size of a DCD frame 
+    cdef readonly int _framesize
+    # Size of the DCD header
+    cdef readonly int _header_size
+    # Is the file open?
+    cdef int is_open
+    # Have we reached the end of the file
+    cdef int reached_eof
+    # Have we written the header?
+    cdef int wrote_header
+    # Are buffers set up?
+    cdef int _buffers_setup
+
+
+    # buffer for reading coordinates
+    cdef np.ndarray _coordinate_buffer
+    # buffer for reading unitcell     
+    cdef np.ndarray _unitcell_buffer
+
+    # fortran contiguious memoryviews of the buffers to pass to the C code
+    cdef float[::1] xview
+    cdef float[::1] yview
+    cdef float[::1] zview
+    cdef double[::1] unitcellview
+
+    cdef void _setup_buffers(self)
+
+    cdef void _read_header(self)
+    # Estimate the number of frames
+    cdef int _estimate_n_frames(self)
+    # Helper to read current DCD frame
+    cdef int c_readframes_helper(self, float[::1] x,
+                                 float[::1] y, float[::1] z,
+                                 double[::1] unitcell, int first_frame)
+
+# Helper in readframes to copy given a specific memory layout
+cdef void copy_in_order(float[:, :] source, float[:, :, :] target, int order, int index)