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--- dev:codingconventions [2018/12/19 11:34] – raise recommended MPI standard to 3, drop recommendation about OOP tmueller
+++ dev:codingconventions [2020/02/11 12:00] – oschuett
@@ Line 3: / Line 3: @@
 ===== Stick to the standard =====
-  * Code enabled by default should be standard Fortran2003 [-std=f2003]
+  * Code enabled by default should be standard Fortran 2008 [-std=f2008] and C99 [-std=c99]
-  * 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 3 of the standard
+  * MPI should should follow version 3 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 =====
@@ Line 39: / Line 39: @@
 ===== Use existing infrastructure =====
+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 the full-matrix ''fm''-package instead of calling BLAS or Scalapack directly.