The  %F_FLOAT  directive  produces  a  VAX  F_floating   literal
  regardless   of  the  current  floating  point  default  of  the
  compilation.  Without the directive,  the  format  of  a  single
  precision  floating  literal  will  be  determined  based on the
  setting of the /FLOAT DCL qualifier or the [FLOAT]  module-level
  attribute.  The syntax is:

    %F_FLOAT floating-point-literal

  For example,

    lib$wait(%f_float 1.0);

  will ensure the correct floating literal for  LIB$WAIT  even  on
  OpenVMS I64 systems which default to IEEE floating format.