IEEE Interface Notes
--------------------

The IEEE standard defines different types of rounding modes and
exception handling but it does not specify an API for controlling
these features. Each platform has its own way of accessing them. The
functions in this directory present a uniform interface to the various
systems in use today. In order to do this only the
"lowest-common-denominator" features are supported.

This directory offers support for 

   setting the rounding precision
   setting the rounding direction
   setting exception handling flags

Even among this basic set there are some features which are not
supported on all platforms.

All the platform-dependent functionality is provided through the
single function

  int gsl_ieee_set_mode (int precision, int rounding, int exception_mask)

where precision, rounding and exception mask are enums defined in
gsl_ieee_utils.h,

  GSL_IEEE_SINGLE_PRECISION
  GSL_IEEE_DOUBLE_PRECISION
  GSL_IEEE_EXTENDED_PRECISION

  GSL_IEEE_ROUND_TO_NEAREST
  GSL_IEEE_ROUND_DOWN
  GSL_IEEE_ROUND_UP
  GSL_IEEE_ROUND_TO_ZERO

  GSL_IEEE_MASK_INVALID
  GSL_IEEE_MASK_DENORMALIZED
  GSL_IEEE_MASK_DIVISION_BY_ZERO
  GSL_IEEE_MASK_OVERFLOW
  GSL_IEEE_MASK_UNDERFLOW
  GSL_IEEE_TRAP_INEXACT

For the mask/traps you can 'or' the numbers together for the desired
combination.

How to add IEEE support for other platforms
-------------------------------------------

The platform support is in the files fp-linux.c, fp-hpux.c,
fp-solaris.c, fp-sunos4.c, etc. Each of these files sets the IEEE mode
based on the arguments above. Look at the files to determine which is
closest to want you want. Write the corresponding source file (e.g.
fp-mysystem.c for the examples below).

The file is chosen from the preprocessor definitions in fp.c. Add an
#elif defined(HAVE_MYSYSTEM_IEEE_INTERFACE) ... section which includes
your file.

    #include <config.h>

    #if defined(HAVE_LINUX_IEEE_INTERFACE)
    #include "fp-linux.c"
    #elif defined(HAVE_HPUX_IEEE_INTERFACE)
    #include "fp-hpux.c"
    #elif defined(HAVE_SUNOS4_IEEE_INTERFACE)
    #include "fp-sunos4.c"
    #elif defined(HAVE_SOLARIS_IEEE_INTERFACE)
    #include "fp-solaris.c"
    #elif defined(HAVE_MYSYSTEM_IEEE_INTERFACE)
    #include "fp-mysystem.c"
    #else
    #include "fp-unknown.c" 
    #endif

Add corresponding definitions in the top-level acconfig.h,

    /* Define one of these if you have a known IEEE arithmetic interface */
    #undef HAVE_LINUX_IEEE_INTERFACE
    #undef HAVE_SUNOS4_IEEE_INTERFACE
    #undef HAVE_SOLARIS_IEEE_INTERFACE
    #undef HAVE_HPUX_IEEE_INTERFACE
    #undef HAVE_MYSYSTEM_IEEE_INTERFACE

Finally edit configure.in to add a test for your system based on the
host-identifier,

    AC_MSG_CHECKING(for IEEE arithmetic interface type)
    case "$host" in
	*-*-linux*) 
	    AC_DEFINE(HAVE_LINUX_IEEE_INTERFACE)
	    AC_MSG_RESULT([linux]) 
	    ;;
	*-*-sunos4*) 
	    AC_DEFINE(HAVE_SUNOS4_IEEE_INTERFACE)
	    AC_MSG_RESULT([sunos4]) 
	    ;;
	*-*-solaris*) 
	    AC_DEFINE(HAVE_SOLARIS_IEEE_INTERFACE)
	    AC_MSG_RESULT([solaris]) 
	    ;;
	*-*-hpux*) 
	    AC_DEFINE(HAVE_HPUX_IEEE_INTERFACE)
	    AC_MSG_RESULT([hpux]) 
            ;;
	*-*-mysystem*) 
	    AC_DEFINE(HAVE_MYSYSTEM_IEEE_INTERFACE)
	    AC_MSG_RESULT([mysystem]) 
	    ;;
	*)
	    AC_MSG_RESULT([unknown])
	    ;;
      esac
	
This should be all that's needed. If your system doesn't support one
of the basic features you can use the error macro GSL_ERROR with an
error number of GSL_EUNSUP. e.g.

    GSL_ERROR ("MYSYS only supports single precision rounding", GSL_EUNSUP);