###################################################################################################
# GNU Compiler
###################################################################################################

  if (OPENMP)
    set (OPENMP_FLAGS "-fopenmp")
  endif ()

  if (OPTIMIZATION STREQUAL "OFF")
    set (OPTIMIZATION_FLAGS "-O0"       )
  elseif (OPTIMIZATION STREQUAL "DEFENSIVE")
    set (OPTIMIZATION_FLAGS "-O2")
  elseif (OPTIMIZATION STREQUAL "AGGRESSIVE")
    set (OPTIMIZATION_FLAGS "-O3 -ffast-math -funroll-loops -ftree-vectorize")
  endif ()

  set (STANDARD_CHECK "-std=f2008ts -pedantic-errors" )
  set (LINKER_FLAGS  "${LINKER_FLAGS} -Wl")
  # options parsed directly to the linker
  set (LINKER_FLAGS  "${LINKER_FLAGS},-undefined,dynamic_lookup" )
  #   ensure to link against dynamic libraries

#------------------------------------------------------------------------------------------------
# Fine tuning compilation options
  set (COMPILE_FLAGS "${COMPILE_FLAGS} -xf95-cpp-input")
  # preprocessor

  set (COMPILE_FLAGS "${COMPILE_FLAGS} -ffree-line-length-132")
  # restrict line length to the standard 132 characters (lattice.f90 require more characters)

  set (COMPILE_FLAGS "${COMPILE_FLAGS} -fimplicit-none")
  # assume "implicit none" even if not present in source

  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wall")
  # sets the following Fortran options:
  #   -Waliasing:                   warn about possible aliasing of dummy arguments. Specifically, it warns if the same actual argument is associated with a dummy argument with "INTENT(IN)" and a dummy argument with "INTENT(OUT)" in a call with an explicit interface.
  #   -Wampersand:                  checks if a character expression is continued proberly by an ampersand at the end of the line and at the beginning of the new line
  #   -Warray-bounds:               checks if array reference is out of bounds at compile time. use -fcheck-bounds to also check during runtime
  #   -Wconversion:                 warn about implicit conversions between different type
  #   -Wsurprising:                 warn when "suspicious" code constructs are encountered. While technically legal these usually indicate that an error has been made.
  #   -Wc-binding-type:
  #   -Wintrinsics-std:             only standard intrisics are available, e.g. "call flush(6)" will cause an error
  #   -Wno-tabs:                    do not allow tabs in source
  #   -Wintrinsic-shadow:           warn if a user-defined procedure or module procedure has the same name as an intrinsic
  #   -Wline-truncation:
  #   -Wtarget-lifetime:
  #   -Wreal-q-constant:            warn about real-literal-constants with 'q'  exponent-letter
  #   -Wunused:                     a number of unused-xxx warnings
  # and sets the general (non-Fortran options) options:
  #   -Waddress
  #   -Warray-bounds (only with -O2)
  #   -Wc++11-compat
  #   -Wchar-subscripts
  #   -Wcomment
  #   -Wformat
  #   -Wmaybe-uninitialized
  #   -Wnonnull
  #   -Wparentheses
  #   -Wpointer-sign
  #   -Wreorder
  #   -Wreturn-type
  #   -Wsequence-point
  #   -Wstrict-aliasing
  #   -Wstrict-overflow=1
  #   -Wswitch
  #   -Wtrigraphs
  #   -Wuninitialized
  #   -Wunknown-pragmas
  #   -Wunused-function
  #   -Wunused-label
  #   -Wunused-value
  #   -Wunused-variable
  #   -Wvolatile-register-var

  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wextra")
  # sets the following Fortran options:
  #   -Wunuses-parameter:
  #   -Wcompare-reals:
  # and sets the general (non-Fortran options) options:
  #   -Wclobbered
  #   -Wempty-body
  #   -Wignored-qualifiers
  #   -Wmissing-field-initializers
  #   -Woverride-init
  #   -Wsign-compare
  #   -Wtype-limits
  #   -Wuninitialized
  #   -Wunused-but-set-parameter (only with -Wunused or -Wall)
  #   -Wno-globals

  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wcharacter-truncation")
  # warn if character expressions (strings) are truncated

  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wunderflow")
  # produce a warning when numerical constant expressions are encountered, which yield an UNDERFLOW during compilation

  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wsuggest-attribute=pure")
  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wsuggest-attribute=noreturn")
  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wconversion-extra")
  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wimplicit-procedure")
  set (COMPILE_FLAGS "${COMPILE_FLAGS} -Wno-unused-parameter")
  set (COMPILE_FLAGS "${COMPILE_FLAGS} -ffpe-summary=all")
  # print summary of floating point exeptions (invalid,zero,overflow,underflow,inexact,denormal)

  # Additional options
  # -Warray-temporarieswarnings:   because we have many temporary arrays (performance issue?):
  # -Wimplicit-interface:          no interfaces for lapack/MPI routines
  # -Wunsafe-loop-optimizations:   warn if the loop cannot be optimized due to nontrivial assumptions.

#------------------------------------------------------------------------------------------------
# Runtime debugging
  set (DEBUG_FLAGS "${DEBUG_FLAGS} -ffpe-trap=invalid,zero,overflow")
  # stop execution if floating point exception is detected (NaN is silent)

  set (DEBUG_FLAGS "${DEBUG_FLAGS} -g")
  # Generate symbolic debugging information in the object file

  set (DEBUG_FLAGS "${DEBUG_FLAGS} -fbacktrace")
  set (DEBUG_FLAGS "${DEBUG_FLAGS} -fdump-core")
  set (DEBUG_FLAGS "${DEBUG_FLAGS} -fcheck=all")
  # checks for (array-temps,bounds,do,mem,pointer,recursion)

  # Additional options
  # -ffpe-trap=precision,denormal,underflow
#------------------------------------------------------------------------------------------------
#  precision settings
  set (PRECISION_FLAGS "${PRECISION_FLAGS} -fdefault-real-8")
  # set precision to 8 bytes for standard real (=8 for pReal). Will set size of double to 16 bytes as long as -fdefault-double-8 is not set
  set (PRECISION_FLAGS "${PRECISION_FLAGS} -fdefault-double-8")
  # set precision to 8 bytes for double real, would be 16 bytes if -fdefault-real-8 is used