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dev:codingconventions [2015/10/15 11:56]
oschuett [Don't use poorly designed language features]
dev:codingconventions [2018/12/21 08:41] (current)
tmueller [Use existing infrastructure]
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 ====== Coding Conventions ====== ====== Coding Conventions ======
 +
 ===== Stick to the standard ===== ===== Stick to the standard =====
-  ​* Code enabled by default should be standard ​Fortran2003 ​[-std=f2003] + 
-  * Avoid using new OOP aspects, because compilers do not yet support them well enough. +  ​* Code enabled by default should be standard ​Fortran 2008 [-std=f2008
-  * OpenMP code should follow ​the version 3.X of the standard +  * OpenMP code should follow version 3.X of the standard 
-  * MPI should should follow ​the version ​2.X of the standard +  * MPI should should follow version ​of the standard 
-  * Extended functionality should match [[wp>​POSIX]] ​[[wp>​Linux_Standard_Base|LSB]].+  * Extended functionality should match [[wp>​POSIX]] ​and [[wp>​Linux_Standard_Base|LSB]].
  
 ===== Write explicit code ===== ===== Write explicit code =====
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     * INTEGER i=4.9999, i.e. i=INT(4.9999) implies i==4. Use NINT(4.9999) as appropriate.     * INTEGER i=4.9999, i.e. i=INT(4.9999) implies i==4. Use NINT(4.9999) as appropriate.
     * natom*natom,​ nrow_global*ncol_global overflows INT(KIND=4) for large simulations.     * natom*natom,​ nrow_global*ncol_global overflows INT(KIND=4) for large simulations.
 +    * always use REAL() with KIND parameter, i.e. r = REAL(i, KIND=dp).
 +    * avoid FLOAT() in favour of REAL(, KIND=dp).
     * the global number of grid points (pw_grid_type%ngpts,​ngpts_cut) overflows INT(KIND=4) for large simulations.     * the global number of grid points (pw_grid_type%ngpts,​ngpts_cut) overflows INT(KIND=4) for large simulations.
  
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 ===== Use existing infrastructure ===== ===== Use existing infrastructure =====
-For many common ​operation ​there exist wrappers in CP2K to prevent usage errors and to allow for central redirections.+ 
 +Always prefer [[https://​gcc.gnu.org/​onlinedocs/​gcc-8.2.0/​gfortran/​Intrinsic-Procedures.html|built-in (intrinsic) functions]] instead of hand-coded routines since they usually include extra numerical checks to avoid intermediate under- or overflow while still performing optimally. Examples: 
 + 
 +  * ''​NORM2(x)''​ instead of ''​%%SQRT(x(1)**2 + x(2)**2 + x(3)**2)%%''​ 
 +  * ''​DOT_PRODUCT(x,​ x)''​ instead of ''​%%x(1)**2 + x(2)**2 + x(3)**2%%''​ 
 +  * ''​DOT_PRODUCT(x,​ y)''​ instead of ''​%%x(1)*y(1) + x(2)*y(2) + x(3)*y(3)%%''​ 
 + 
 + 
 +For many common ​operations ​there exist wrappers in CP2K to prevent usage errors and to allow for central redirections, i.e. avoid to use direct calls to external libraries in CP2K 
   * Use the routines from ''​cp_files.F''​ instead of calling ''​OPEN''​ and ''​CLOSE''​ directly.   * Use the routines from ''​cp_files.F''​ instead of calling ''​OPEN''​ and ''​CLOSE''​ directly.
   * Use the routines from the full-matrix ''​fm''​-package instead of calling BLAS or Scalapack directly.   * Use the routines from the full-matrix ''​fm''​-package instead of calling BLAS or Scalapack directly.
   * Use the routines from ''​message_passing.F''​ instead of calling MPI directly.   * Use the routines from ''​message_passing.F''​ instead of calling MPI directly.
 +  * Use the routines from ''​fft_lib.F''​ instead of calling FFT (any library) directly.
   * Use the routines from ''​machine.F''​ to access architecture depended things like e.g. the working directory.   * Use the routines from ''​machine.F''​ to access architecture depended things like e.g. the working directory.
   * Don't use ''​UNIT=*''​ in ''​WRITE''​ or ''​PRINT''​ statements. Instead request a unit from the logger: ''​iw=cp_logger_get_default_unit_nr()''​ and write only if you actually received a unit: ''​IF(iw>​0) WRITE (UNIT=iw, ,,,​)''​.   * Don't use ''​UNIT=*''​ in ''​WRITE''​ or ''​PRINT''​ statements. Instead request a unit from the logger: ''​iw=cp_logger_get_default_unit_nr()''​ and write only if you actually received a unit: ''​IF(iw>​0) WRITE (UNIT=iw, ,,,​)''​.
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 ===== Remove dead code ===== ===== Remove dead code =====
-Every line of code has to be compiled and maintained. Hence, unused variables and code poses an unnecessary burden and should be removed. ​However, sometimes ​it is beneficial to keep debugging code around. Such code should be put into a ''​IF(debug_this_module)''​-block,​ with a parameter set to ''​.FALSE.''​. This way the code will stay up-to-date and easily callable.+  * Every line of code has to be compiled and maintained. Hence, unused variables and code poses an unnecessary burden and should be removed ​[-Wunused-variable -Wunused-but-set-variable -Wunused-dummy-argument]. 
 +  * Sometimes ​it is beneficial to keep debugging code around ​nevertheless. Such code should be put into a ''​IF(debug_this_module)''​-block,​ with a parameter set to ''​.FALSE.''​. This way the code will stay up-to-date and easily callable.
  
 ===== Format and document code ===== ===== Format and document code =====
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   * Each module and routine should be annotated with [[dev:​codingconventions#​Doxygen| Doxygen documentation]].   * Each module and routine should be annotated with [[dev:​codingconventions#​Doxygen| Doxygen documentation]].
   * Each preprocessor flag should start with two underscores and be documented in the ''​INSTALL''​-file and added to the cp2k_flags function (cp2k_info.F).   * Each preprocessor flag should start with two underscores and be documented in the ''​INSTALL''​-file and added to the cp2k_flags function (cp2k_info.F).
-  * The code should be formatted with the prettify-tool by running ''​make -j pretty''​. +  * The code should be formatted with the [[dev:​formattingconventions| ​prettify tool]] by running ''​make -j pretty''​.
 ===== Write tests ===== ===== Write tests =====
   * Every feature should be tested, with the goal of complete [[ http://​www.cp2k.org/​static/​coverage/​ | code coverage by regtesting ]].   * Every feature should be tested, with the goal of complete [[ http://​www.cp2k.org/​static/​coverage/​ | code coverage by regtesting ]].
dev/codingconventions.1444910214.txt.gz · Last modified: 2015/10/15 11:56 by oschuett