/DOUBLE_SIZE

  The /DOUBLE_SIZE qualifier lets you specify the data size for
  floating-point DOUBLE PRECISION data declarations.  You can specify
  64 or 128 for "n".

  To request that all DOUBLE PRECISION declarations, constants,
  functions, and intrinsic procedures use the REAL(KIND=16)
  extended-precision data, specify /DOUBLE_SIZE=128.  REAL(KIND=16)
  data is stored in memory using X_floating format.

  The default is /DOUBLE_SIZE=64, which specifies that DOUBLE
  PRECISION entities use REAL(KIND=8) (64-bit) double-precision data.
  To select the floating-point format used in memory for 64-bit
  REAL(KIND=8) data, use the /FLOAT qualifier.