File: STANDARDS

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Copyright (C) 2001-2010 Roberto Bagnara <bagnara@cs.unipr.it>
Copyright (C) 2010-2016 BUGSENG srl (http://bugseng.com)
See below for the copying conditions.


Coding Standards for the Parma Polyhedra Library
================================================

Please read the first chapters of "Ada 95 Quality and Style:
Guidelines for Professional Programmers" (you will find a link to it
in the "Links" section of the PPL web site).


Names
-----

Carefully choose names that clarify the nature or the intended use of
the entity you are naming.  Do not be afraid of long identifiers, even
though conciseness is always a good thing.  Do not use abbreviations
when shorter synonyms exist.  Use underscores to separate words in a
compound name.  By all means, avoid baStudlyCaps: write
available_widening_tokens (if it is a variable) or
Available_Widening_Tokens (if it is a class or enum); never write
availableWideningTokens or AvailableWideningTokens.
In general, we use:

  lower_case for variables, methods, functions, typedefs;
  UPPER_CASE for macros and enum values;
  Mixed_Case for class names and template parameter names.


Pre and post increment and decrement operators
----------------------------------------------

All other things being equal, always prefer preincrement and
predecrement to postincrement and postdecrement.


Swap specialization
-------------------

All library types should provide a publicly available swap method.
Whenever appropriate for ensuring efficiency, the generic std::swap
algorithm should be specialized to use the swap method.


Limiting the visibility of variables, functions, macros and so forth
--------------------------------------------------------------------

Avoid using the keyword `static' to specify that global variables or
functions should be visible only inside the current translation unit;
use the anonymous namespace, instead. The keyword `static' should
only appear inside class definitions or function bodies. As an example,

static const char* s = "Not accessible by other translation units";

static void f() {
  // ... function body ...
}

should be replaced by

namespace {

const char* s = "Not accessible by other translation units";

void f() {
  // ... function body ...
}

} // namespace

However, do not use anonymous namespaces in a header file
(any file that is meant to be included in other translation units).
Instead, define and use a new non-anonymous namespace that should
be placed inside the namespace

    Parma_Polyhedra_Library::Implementation

Concerning macros and the implementation languages (such as C and Prolog)
that have a flat identifiers namespace, make sure the library limits
its impact as much as possible by naming objects in a conspicuous way
and by limiting as much as possible the scope of declarations.
This means

- all C and C++ macros should have names prefixed by `PPL_';
  those that are not meant to be directly accessible by the user should
  be #undef'ed as soon as possible in the source file they are defined in;
- all functions and types declared by the C interface should have
  names prefixed by `ppl_';
- all Prolog predicates declared by the Prolog interfaces should have
  names prefixed by `ppl_'.


Macros
------

Macros should be used only if really needed (in many cases, macros can
be replaced by inline functions).


Block closures
--------------

Try to make clear what is being closed.  For example:

1)

namespace Parma_Polyhedra_Library {

...

} // namespace Parma_Polyhedra_Library

2)

extern "C" {

...

} // extern "C"

3)

#ifndef PPL_Class_defs_hh

...

#endif // !defined(PPL_Class_defs_hh)


Negation
--------

Use `!' to negate a value.

For example, use

        if (!ph.is_empty())
           std::cout << "ph contains at least one point" << endl;

instead of

        if (ph.is_empty() == false)
           std::cout << "ph contains at least one point" << endl;


Comparison with zero
--------------------

Be explicit when comparing a value with zero in a conditional context.

For example, use

        assert(sys.num_rows() != 0);

instead of

        assert(sys.num_rows());


Formatting Conventions
======================

Indent each level using two spaces.
Insert a space: after each comma, before and after each operator, after
if/do/while keywords. As an exception to this rule, spaces can be omitted near
arithmetic multiplication and division operator, if they would harm
readability.
Don't insert spaces between the name of a function and the following
parenthesis.
Braces should be cuddled on the preceding/following line.
Avoid, when possible, source lines longer than 78 characters.
In a function declaration, the return type of a function and the modifiers
must be placed alone in one line.
In pointer and reference types, the * and & characters should be followed, but
not preceded, by a space.

This is bad:

inline void C::f(int *x,int y)
{
if( x!=0 )
{
    int &z=y;
    foo (x / 2+y * 3,z/bar(5));
}
}

This is good:

inline void
C::f(int* x, int y) {
  if (x != 0) {
    int& z = y;
    foo(x/2 + y*3, z / bar(5));
  }
}


Namespace indentation
---------------------

The entire library is in its own namespace.  We sometimes specialize
std::swap() and std::iter_swap().  Other namespaces may be involved
but only in restricted contexts.  Therefore, we have unindented
namespace-level declarations, thus saving some precious horizontal
space.  For example:

namespace Parma_Polyhedra_Library {

non-empty lines here start at column 0;

} // namespace Parma_Polyhedra_Library

If you use Emacs, you may want to put the following two lines in your
.emacs:

;; Disable indentation when in namespace blocks.
(c-set-offset 'innamespace 0)


Trailing whitespace
-------------------

Always avoid trailing whitespace.
If you use Emacs, then all the trailing whitespace in the current
buffer can be removed by using the command

  M-x delete-trailing-whitespace

If you keep inserting trailing whitespace when coding, then you may
want to put the following two lines in your .emacs:

;; Show trailing whitespace.
(setq-default show-trailing-whitespace t)


Standards for Structuring the Source Code in Files
==================================================

Source code should be organized so as to ensure that:
  - the contents of a file are strongly related;
  - each file is of manageable size.

As a rule of thumb, each type (class, struct, class template, etc.)
named `Xtype' that is relevant on its own for the user or the
developer of the library should be provided with a set of source files
whose filenames start with `Xtype'. The source files for such a type
should be named and populated as follows:

a) Xtype_types.hh
Contains the forward declarations of type names (in particular, the
one for `Xtype') and other useful typedef's.

b) Xtype_defs.hh
Contains the definition of the type, together with the declaration of
any function that, even though not being formally part of the type, is
nonetheless related to it and should therefore be considered part of
its interface.

c) Xtype_inlines.hh
Contains the definitions of inline functions.

d) Xtype_templates.hh
Contains the non-inline definitions of all class template members and
all (member or non-member) function templates that are not fully
specialized.

e) Xtype.cc
Contains the definitions of non-inline functions, including non-inline
full specializations of templates.

f) When appropriate, further *.cc files can be used to split huge
source files into more manageable components (e.g., see the files
Polyhedron_public.cc, Polyhedron_nonpublic.cc, Polyhedron_chdims.cc
and Polyhedron_widenings.cc, or even conversion.cc, minimize.cc, etc.).

Note that:
  - all interface functions should be declared in Xtype_defs.hh;
  - no function definition should be placed in Xtype_defs.hh;
  - bare declarations should not be declared inline (i.e., inline directives
    should be placed only in front of the definition of the functions);
  - inner classes are usually kept in the same files as the outer class;
  - functions having the anonymous namespace scope can be (and usually are)
    only declared and defined in file Xtype.cc, regardless of whether or not
    the inline directive is specified.


Standards for Writing the Makefile.am Files
===========================================

How to clean what
-----------------

Cleaning in this context means removing files from the build directory.
In order to clean files, they must be listed in one of three variables:
MOSTLYCLEANFILES, CLEANFILES and DISTCLEANFILES.  The rules (believed to
have been first formulated by Francois Pinard) are:

  - If `make' built the file, and it is commonly something that one would
    want to rebuild (such as an object file), then list the file in
    MOSTLYCLEANFILES.
  - Otherwise, if `make' built the file, then list it in CLEANFILES.
  - Otherwise, if `configure' built the file, then list it in DISTCLEANFILES.

When cleaning is more complex than a simple deletion, you can use the hooks
mostlyclean-local, clean-local and distclean-local.


Standards for Documenting the Project with Doxygen
==================================================

1) All code entities (classes, structs, enums, variables, methods,
   functions, etc.) should be provided with a brief Doxygen comment.
   Brief comments are normally obtained as follows:

     //! Brief comment for class C.
     class C {
       ...
     };

   If the comment is multi-line, then the following syntax should be adopted:

     /*! \brief
       A brief comment for class C, that is a bit too long
       to be placed in a single line.
     */
     class C {
       ...
     };

2) A *friend* declaration of a function should NOT be provided with
   a Doxygen comment. Rather, it is the very declaration of the function
   (which should be found outside of the class) that has to be documented.

3) When needed or useful, brief comments should be followed by detailed
   Doxygen comments. If the brief comment spans a single line of text, then
   the following syntax can be adopted:

     //! Brief comment for class C.
     /*!
       More details on class C.
       Even more details.
     */
     class C {
       ...
     };

   Otherwise, if the brief comment spans multiple lines of text, the
   following syntax should be adopted, where the brief and the detailed
   documentation are merged in a single multiline comment block:

     /*! \brief
       Brief comment for class C.

       More details on class C.
       Even more details.
     */
     class C {
       ...
     };

   The first paragraph break (in this case, the empty line) marks the
   separation between the brief and the detailed part. Note that
   all the uses of \param, \result and \exception special commands
   will automatically cause a paragraph break, therefore starting
   the detailed part. This will happen even when using the //! style
   documentation blocks.

4) In the produced documentation, the brief comment will be
   automatically repeated just before the detailed comment,
   so that bare repetitions should be avoided.

5) In the source files, detailed comments should be placed together
   with the brief ones, so that all the documentation pertinent to a
   code entity is kept in a single file (typically, the *_defs.hh file).

6) Brief Doxygen comments should be brief (indeed).
   If more than two lines are required, then the comment should be
   split into a brief part and a detailed part.

7) Code entities or details that should not be visible to the end-user
   (but that are useful for the developers) should be surrounded by

     #ifdef PPL_DOXYGEN_INCLUDE_IMPLEMENTATION_DETAILS
        //! ... Doxygen comments ...
     #endif // PPL_DOXYGEN_INCLUDE_IMPLEMENTATION_DETAILS

   so that they will only appear in the developer's reference.
   Note that the above preprocessing flags are not necessary
   (and should therefore be avoided) when documenting:
    - a private member of a class (because private members never
      appear in the user manual);
    - a public member of a class that is not documented
      (because even the documented members of an undocumented
      class are automatically filtered out of the user manual).

8) Merging multiple comment blocks is not (fully) supported by Doxygen.
   Thus, the technique described in point 4) above is useless
   when we want an end-user comment block to be integrated,
   in the developer's reference only, by further comments.
   In such a case, a single comment block should be used as follows:

     /*!
       ... Doxygen comments for both user and developer ...
       \if Include_Implementation_Details
       ... Doxygen comments for developer only ...
       \endif
       ... Doxygen comments for both user and developer ...
     */

9) The documentation of those functions that are neither methods
   nor friends of a given class, but are related in some way to that
   class, should be made part of the documentation of the class.
   This is obtained by using the Doxygen \relates special command
   as follows:

     /*! \relates Classname */

   It seems that, in order to correctly match function declarations
   and definitions, the \relates command should be placed in both places.
   Typically, this will be the only kind of Doxygen command
   occurring in *_inlines.hh and *.cc source files.

   If Classname is a template class, the arguments of the template
   (as well as the angle brackets) should be omitted.
   The namespace qualification of the class can be omitted, provided
   the comment block is included in the namespace scope.

10)
  If the \return or \param special commands are used, then these have to
  be placed after the brief Doxygen comment.  The \return special
  command, if present, should come before any \param command.  The
  \exception special command, if present, should come after any \param
  command. All the parameters of the function should be provided by the
  corresponding \param command, respecting their textual order,
  separating them with a blank line.  The documentation of each
  parameter should start at the line immediately following the \param
  command.  Typically, the list of parameters should be formatted as
  follows, where the \return command is optional.

  /*! \brief
    The brief description.

    The detailed description, if any.

    \return
    Documentation for the return value, if provided.

    \param p1
    Documentation for p1;

    \param p2
    Documentation for p2;
    other documentation for p2;

    \param p3
    Documentation for p3.

    \exception exception_type1
    Documentation for the exceptions of type exception_type1;

    \exception exception_type2
    Documentation for the exceptions of type exception_type2.

    Another piece of detailed description, if needed.
  */
  int foo(const bar& p1, const bar& p2, int p3);


Standards for the Test Programs
===============================

o  Include the header file `ppl_test.hh' to include common declarations
   for test code (see below).

o  Place the test code in test functions that return a Boolean value.
   Name the test functions test01, test02, etc.

o  Each test program should contain no more than 20 test functions.

o  The test functions should be written

        // Comment describing the test...
        bool
        test10() {
            // ... test code ...
        }

   where the 10 in `test10' indicates that it is the 10th test function
   in the program.

o  The test functions should return true if the test succeeds and false
   if it fails.

o  If a test requires auxiliary functions and/or classes, put them
   in a namespace named, e.g., `test10_namespace', which in turn is
   within the anonymous namespace.

o  Following all the test functions, include:

        BEGIN_MAIN
          DO_TEST(test01);
          DO_TEST(test02);
          ...
        END_MAIN

   where every test function in the program is included in the list.

o  If any of the tests is known to fail due to an overflow when the
   library is configured to use some of the bounded-precision checked
   integers, then the corresponding test function should be called,
   e.g., as follows

          DO_TEST_F32(test07);

   where the subscript "_F32" means that the overflow is expected for
   all checked integers having 32 bits at most (i.e., 64 bits checked
   integers are not expected to overflow). As an alternative,

          DO_TEST_F32A(test07);

   means that the overflow is expected, as before, for all checked
   integers having less than 32 bits but in the case of 32 bits checked
   integers the overflow occurs only if assertions are enabled.
   Hence, the possible subscripts for DO_TEST are:

          _F8A, _F8, _F16A, _F16, _F32A, _F32, _F64A, _F64.

o  If any of the tests _may_ fail due to an overflow (when the library
   is configured to use some of the bounded-precision checked integers)
   when a templatic shape domain is instantiated using inexact
   coefficients (e.g., the typedef TBD_Shape stands for BD_Shape<float>),
   then the corresponding test function should be called as follows

          DO_TEST_MAY_OVERFLOW_IF_INEXACT(test07, TBD_Shape);

o  If a definite overflow (i.e., independent from exactness) is expected
   for some of the coefficient sizes, then the two macro names above
   can be combined, e.g., as follows

          DO_TEST_F16_MAY_OVERFLOW_IF_INEXACT(test07, TBD_Shape);

   meaning that the overflow is expected for 16 (or fewer) bits
   configurations, while it may occur for configurations using more bits
   if the shape domain is instantiated usng inexact coefficients.

o  Normally, test code should produce no output at all (independently from
   whether the test succeeded or failed). Output is only meant to help
   during debugging. In order to support for the coding of conditional
   output, the header file `ppl_test.hh' defines the output streams `nout'
   and `vnout'. By default, any output directed to these streams will be
   simply discarded. For example,

        nout << "A message when noisy." << endl;
        vnout << "A message when very noisy." << endl;

   will produce no output at all. By default, the helper print functions
   (e.g., print_constraints, print_generators, etc.) are directed to
   stream `nout', so that they will normally discard the output too.

o  By defining the environment variables `PPL_NOISY_TESTS' and/or
   `PPL_VERY_NOISY_TESTS' to any value, the streams `nout' and `vnout'
   will be redirected to standard output and become noisy.

o  On very weird platforms the above mechanism may not be supported.
   In these rare cases, the same effect can be obtained by defining
   the preprocessor variables NOISY and/or VERY_NOISY to any value other
   than zero and recompiling the test program.  Thus, if some output is
   (locally and temporarily) needed for debugging purposes, one option
   is to add

      #define NOISY 1
      #define VERY_NOISY 1

   as the very first line of the test source file and recompile it.

o  To avoid repeated namespace qualifications, the header file `ppl_test.hh'
   adds a using directive for the whole PPL namespace. It also adds a
   using declaration for `std::endl'. All the other objects defined in
   the namespace `std' should be explicitly qualified in the test files
   (typically, by adding a corresponding using declaration).

o  If PPL stream input and output is required, then an explicit using
   directive for the Parma_Polyhedra_Library::IO_Operators namespace
   should be added to the test file.

o  Refer to the existing tests for examples. Many tests are written along
   the following schema:
     a) create a PPL object and perform some computations with it;
     b) create a second object in a different (maybe simpler) way, having
        as value the expected result of the computations done in point a);
     c) check for equivalence of the two objects.

o  Ideally the tests should exercise every line of code in the library.
   To help ensure that, the test-coverage facilities provided by GCC
   are very useful.  They are described in Chapter 9 of the GCC manual
   ("`gcov'---a Test Coverage Program").  For a simpler user interaction
   with gcov, also including the generation of nicer HTML output, the
   adoption of `lcov' is recommended (LCOV, the Linux Test Project GCOV
   extension, http://ltp.sourceforge.net/coverage/lcov.php).
   Here we summarize the steps needed to produce coverage information
   using `lcov' (see below for a few hints on the direct use of `gcov').
   The build tree under test must be configured with the
   `--enable-coverage' and `--disable-optimization' options (and possibly
   also with --enable-profiling). Furthermore, according to this thread
       http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12076
   GCC performs NRV (Named Return Value) transformations even when
   optimizations are turned off; hence, to avoid spurious zero counts
   in return statements, the compilation flag `-fno-elide-constructors'
   is recommended. For example:

     $ configure --enable-coverage --enable-profiling \
         --disable-optimization --with-cxxflags='-fno-elide-constructors' \
         --enable-assertions --enable-more-assertions

   Running the tests (with `make check') produces many .gcno and .gcda
   files in src/.libs and in the test directories.  These are data
   files for the `gcov' program. All the coverage data produced can be
   automatically collected by `lcov' using the following command:

     $ lcov --directory . --capture --output-file ppl-lcov.info

   To generate HTML pages with the graphical view of the captured data,
   use the `genhtml' command:

     $ genhtml ppl-lcov.info --output-directory ppl-lcov-html

   Coverage info can now be seen by pointing your favorite browser to
   file ppl-lcov-html/index.html. The annotated sources will look like
   the following (plus color information), where the value on the left
   hand side of the colon is the number of executions of the corresponding
   line of code (see also below on the use of coverage counters):

    1636 :   PPL_DIRTY_TEMP(N, sum);
    9828 :   for (dimension_type k = num_dimensions + 1; k-- > 0; ) {
    6556 :     const DB_Row<N>& x_dbm_k = x.dbm[k];
   39648 :     for (dimension_type i = num_dimensions + 1; i-- > 0; ) {
   26536 :       DB_Row<N>& x_dbm_i = x.dbm[i];
   26536 :       const N& x_dbm_i_k = x_dbm_i[k];
   26536 :       if (!is_plus_infinity(x_dbm_i_k))
   55128 :         for (dimension_type j = num_dimensions + 1; j-- > 0; ) {
   36904 :           const N& x_dbm_k_j = x_dbm_k[j];
   36904 :           if (!is_plus_infinity(x_dbm_k_j)) {
         :             // Rounding upward for correctness.
   12136 :             add_assign_r(sum, x_dbm_i_k, x_dbm_k_j, ROUND_UP);
   12136 :             min_assign(x_dbm_i[j], sum);
         :           }
         :         }
         :     }
         :   }

   Note that the collection of coverage information is incremental:
   running again any tests will add to coverage counters (in order
   to see the changes, coverage data has to be re-captured using the
   `lcov' command and HTML pages re-generated using the `genhtml' command).
   Coverage counters can be reset to zero by issuing the command:

     $ lcov --directory . --zerocounters

   As said above, `lcov' is just a wrapper on top of `gcov'. The direct
   use of `gcov' produces plain-text based coverage information.
   For example:

     $ cd src
     $ gcov -o .libs Grid_public.cc

   will produce a file called Grid_public.cc.gcov containing the
   coverage information for Grid_public.cc.  In a similar way

     $ cd tests/Grid
     $ gcov *.cc

   will produce a file call tests/Grid/ppl.hh.gcov containing coverage
   information for the header files.

   Below is a section from a .gcov file.  The first column is the
   number of times the line was run, the second is the line number of the
   line in the source file.  Line 1006 has been run 48245 times.  Lines
   1007, 1002 and 1013 have yet to be run.  It would be very difficult
   to run line 1007, since this requires a Linear_System that does not
   satisfy the invariants for its class and the PPL does everything it
   can to make that impossible without fiddling with memory using raw
   memory pointers.  Similarly for line 1013.  However, the fact that
   line 1012 has never been run is suspicious and may indicate an area
   that needs testing.

        -: 1001:bool
    48245: 1002:PPL::Generator_System::OK() const {
        -: 1003:  // A Generator_System must be a valid Linear_System; do not check for
        -: 1004:  // strong normalization, since this will be done when
        -: 1005:  // checking each individual generator.
    48245: 1006:  if (!Linear_System::OK(false))
    #####: 1007:    return false;
        -: 1008:
        -: 1009:  // Checking each generator in the system.
    48245: 1010:  const Generator_System& x = *this;
    96490: 1011:  for (dimension_type i = num_rows(); i-- > 0; )
    #####: 1012:    if (!x[i].OK())
    #####: 1013:      return false;
        -: 1014:
        -: 1015:  // All checks passed.
    48245: 1016:  return true;
        -: 1017:}


--------

Copyright (C) 2001-2010 Roberto Bagnara <bagnara@cs.unipr.it>
Copyright (C) 2010-2016 BUGSENG srl (http://bugseng.com)

This document describes the Parma Polyhedra Library (PPL).

Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
The license is included, in various formats, in the `doc' subdirectory
of each distribution of the PPL in files named `fdl.*'.

The PPL is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3 of the License, or (at your
option) any later version.  The license is included, in various
formats, in the `doc' subdirectory of each distribution of the PPL in
files named `gpl.*'.

The PPL is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

If you have not received a copy of one or both the above mentioned
licenses along with the PPL, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1307, USA.

For the most up-to-date information see the Parma Polyhedra Library
site: http://bugseng.com/products/ppl/ .