find_mpi() {
  # for MPI, we try to detect system MPI variant
  if (command -v mpiexec > /dev/null 2>&1); then
    export MPI_ENABLED = true
    # check if we are dealing with openmpi, mpich or intelmpi
    if (mpiexec --version 2>&1 | grep -s -q "HYDRA"); then
      echo "MPI is detected and it appears to be MPICH"
      export MPI_MODE="mpich"
      # check openmpi version as reported by mpiexec
      export MPI_VERSION=$(mpiexec --version | grep "Version:" | awk '{print $2}')
      with_mpich="__SYSTEM__"
    elif (mpiexec --version 2>&1 | grep -s -q "OpenRTE"); then
      echo "MPI is detected and it appears to be OpenMPI"
      export MPI_MODE="openmpi"
      # check openmpi version as reported by mpiexec
      export MPI_VERSION=$(mpiexec --version 2>&1 | grep "(Open MPI)" | awk '{print $4}')
      with_openmpi="__SYSTEM__"
    elif (mpiexec --version 2>&1 | grep -s -q "Intel"); then
      echo "MPI is detected and it appears to be Intel MPI"
      export MPI_MODE="intelmpi"
      # check intelmpi version as reported by mpiicc
      export MPI_VERSION=$(mpiexec --version | grep "Version" | awk '{print $8"."$10}')
      with_intelmpi="__SYSTEM__"
    else # default to mpich
      echo "MPI is detected and defaults to MPICH"
      export MPI_MODE="mpich"
      with_mpich="__SYSTEM__"
    fi
  else
    report_warning $LINENO "No MPI installation detected (ignore this message in Cray Linux Environment or when MPI installation was requested)."
    export MPI_MODE=""
  fi
}

# helper routine to check integrity of downloaded files
checksum() {
  local __filename=$1
  local __sha256=$2
  local __shasum_command='sha256sum'
  # check if we have sha256sum command, Mac OS X does not have
  # sha256sum, but has an equivalent with shasum -a 256
  command -v "$__shasum_command" > /dev/null 2>&1 ||
    __shasum_command="shasum -a 256"
  if echo "$__sha256  $__filename" | ${__shasum_command} --check; then
    echo "Checksum of $__filename Ok"
  else
    rm -v ${__filename}
    report_error "Checksum of $__filename could not be verified, abort."
    return 1
  fi
}

# verify the checksums inside the given checksum file
verify_checksums() {
  local __checksum_file=$1
  local __shasum_command='sha256sum'

  # check if we have sha256sum command, Mac OS X does not have
  # sha256sum, but has an equivalent with shasum -a 256
  command -v "$__shasum_command" > /dev/null 2>&1 ||
    __shasum_command="shasum -a 256"

  ${__shasum_command} --check "${__checksum_file}" > /dev/null 2>&1
}

# write a checksum file $1 containing checksums for each given file $2, $3, ... (plus the $VERSION_FILE)
write_checksums() {
  local __checksum_file=$1
  shift # remove output file from arguments to be able to pass them along properly quoted
  local __shasum_command='sha256sum'

  # check if we have sha256sum command, Mac OS X does not have
  # sha256sum, but has an equivalent with shasum -a 256
  command -v "$__shasum_command" > /dev/null 2>&1 ||
    __shasum_command="shasum -a 256"

  ${__shasum_command} "${VERSION_FILE}" "$@" > "${__checksum_file}"
}

# generate a filtered toolchain.env
write_toolchain_env() {
  local __installdir=$1

  # run the following in a subshell to not affect the currently running shell
  # we do not need to achieve complete filtering, it is sufficient to
  # remove problematic variables (TERM/TERMCAP/COLORTERM) which may trigger
  # 'too many arguments' (since the environment vars are stored in the same memory block as command line arguments)
  # or which may not be valid anymore the next time the user runs the toolchain scripts,
  # like the proxy vars which may affect fetching tarballs
  (
    unset COLORTERM DISPLAY EDITOR LESS LESSOPEN LOGNAME LS_COLORS PAGER
    unset TERM TERMCAP USER
    unset ftp_proxy http_proxy no_proxy
    unset GPG_AGENT_INFO SSH_AGENT_PID SSH_AUTH_SOCK SSH_CLIENT SSH_CONNECTION SSH_TTY
    unset LS_COLORS LS_OPTIONS
    unset STY WINDOW XAUTHORITY
    unset XDG_CURRENT_DESKTOP XDG_RUNTIME_DIR XDG_SEAT XDG_SESSION_CLASS XDG_SESSION_DESKTOP XDG_SESSION_ID XDG_SESSION_TYPE XDG_VTNR XDG_CONFIG_DIRS XDG_DATA_DIRS
    unset DBUS_SESSION_BUS_ADDRESS

    export -p
  ) > "${__installdir}/toolchain.env"
}