==============
Bitmask Module
==============

The central part of this module is the ``bitmasks_module.f90`` file. It contains
the constants that will be used to define on which kind of integer the bitmasks
will be defined.

In the program, when an integer ``X`` is used to represent a bit string (like a determinant
for example), it should be defined as, for example:

.. code-block:: fortran

  use bitmasks
  integer(bit_kind)  :: X


The ``bitmasks_routines.irp.f`` contains helper routines to manipulate bitmassk, like
transforming a bit string to a list of integers for example.

Assumptions
===========

.. Do not edit this section. It was auto-generated from the
.. NEEDED_MODULES file.

``bit_kind_shift``, ``bit_kind_size`` and ``bit_kind`` are coherent:

.. code_block:: fortran

  2**bit_kind_shift = bit_kind_size
  bit_kind = bit_kind_size / 8




Needed Modules
==============

.. Do not edit this section. It was auto-generated from the
.. NEEDED_MODULES file.

* `AOs <http://github.com/LCPQ/quantum_package/tree/master/src/AOs>`_
* `Electrons <http://github.com/LCPQ/quantum_package/tree/master/src/Electrons>`_
* `Ezfio_files <http://github.com/LCPQ/quantum_package/tree/master/src/Ezfio_files>`_
* `MOs <http://github.com/LCPQ/quantum_package/tree/master/src/MOs>`_
* `Nuclei <http://github.com/LCPQ/quantum_package/tree/master/src/Nuclei>`_
* `Output <http://github.com/LCPQ/quantum_package/tree/master/src/Output>`_
* `Utils <http://github.com/LCPQ/quantum_package/tree/master/src/Utils>`_

Documentation
=============

.. Do not edit this section. It was auto-generated from the
.. NEEDED_MODULES file.

`full_ijkl_bitmask <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks.irp.f#L/BEGIN_PROVIDER [ integer(bit_kind), full_ijkl_bitmask, (N_int,4) ]/;"
>`_
  Bitmask to include all possible MOs

`hf_bitmask <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks.irp.f#L/BEGIN_PROVIDER [ integer(bit_kind), HF_bitmask, (N_int,2)]/;"
>`_
  Hartree Fock bit mask

`n_int <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks.irp.f#L/BEGIN_PROVIDER [ integer, N_int ]/;"
>`_
  Number of 64-bit integers needed to represent determinants as binary strings

`ref_bitmask <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks.irp.f#L/BEGIN_PROVIDER [ integer(bit_kind), ref_bitmask, (N_int,2)]/;"
>`_
  Reference bit mask, used in Slater rules, chosen as Hartree-Fock bitmask

`bitstring_to_hexa <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks_routines.irp.f#L/subroutine bitstring_to_hexa( output, string, Nint )/;"
>`_
  Transform a bit string to a string in hexadecimal format for printing

`bitstring_to_list <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks_routines.irp.f#L/subroutine bitstring_to_list( string, list, n_elements, Nint)/;"
>`_
  Gives the inidices(+1) of the bits set to 1 in the bit string

`bitstring_to_str <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks_routines.irp.f#L/subroutine bitstring_to_str( output, string, Nint )/;"
>`_
  Transform a bit string to a string for printing

`list_to_bitstring <http://github.com/LCPQ/quantum_package/tree/master/src/Bitmask/bitmasks_routines.irp.f#L/subroutine list_to_bitstring( string, list, n_elements, Nint)/;"
>`_
  return the physical string "string(N_int,2)" from the array of occupations "list(N_int*bit_kind_size,2)
  list
  <== ipos ==>
  |
  v
  string :|------------------------|-------------------------|------------------------|
  <==== bit_kind_size ====> <==== bit_kind_size ====> <==== bit_kind_size ====>
  {        iint            } {         iint         } {         iint         }