DFP.txt

DFP usage notes:

The Advance Toolchain currently provides Decimal Floating Point compiler
and library support in a standalone toolchain.

In order to be able to reference DFP defined symbols (including constants
and functions) one's source code must define the following:

#define __STDC_WANT_DEC_FP__ 1

or build the source with the following define flag:
-D__STDC_WANT_DEC_FP__=1

GNU99 compatibility is required to pick up some DFP prototypes.  It will
define __USE_ISOC99.  Use the following compilation flag:
-std=gnu99

NOTE: -std=gnu99 IS NOT THE SAME AS __USE_ISOC99 though -std=gnu99 DOES
DEFINE __USE_ISOC99!

NOTE: If you forget to use -std=gnu99 you may notice that you will get very
screwy results when you call dfp math functions.  If the compiler can't
find the prototypes (due to missing defines) it will attempt to create a
default prototype which will have the incorrect return type.

The following include files provide the constants and function prototypes
provided by DFP but only when __STDC_WANT_DEC_FP__ is defined to '1'.

	/* fe_dec_getround(), fe_dec_setround(), and rounding mode
	 * enumeration types provided by an implicit #include
	 * <bits/dfpfenv.h to pic.  */
	#include <fenv.h>

	/* All math function prototypes for d32/d64/d128, polymorphic
	 * classification macros, comparison macros, and DEC_NAN and
	 * DEC_INFINITY macros.  This includes an implicit #include
	 * <bits/dfpcalls.h> to pick up new DFP only prototypes defined in
	 * include/bits/dfpcalls.h.  */
	#include <math.h>

	/* Type dependent floating point macros for DFP support
	 * traditionally defined in float.h.  */
	#include <decfloat.h>

The Decimal Floating Point IEEE types are as follows:

	_Decimal32
	_Decimal64
	_Decimal128

The printf format flags follow:

	%H - for _Decimal32
	%D - for _Decimal64
	%DD - for _Decimal128

The scanf format flags follow:

	%DF - for _Decimal32
	%DD - for _Decimal64
	%DL - for _Decimal128

The floating point suffix for DFP constants follows:

	'DF' for _Decimal32, e.g. _Decimal32 d32 = 1.045DF;
	'DD' for _Decimal64, e.g. _Decimal64 d64 = 1.4738273DD;
	'DL' for _Decimal128, e.g. _Decimal128 d128 = 1.0823382394823945DL;

NOTE: Assigning a naked constant to a DFP variable will actually be
performing a binary to decimal conversion and, depending on the precision,
can assign an incorrect number.  Always use the decimal floating point
suffix!

A compilation and link for a DFP program will look like the following:

/opt/at05/bin/gcc test_dfp.c -o dfp -D__STDC_WANT_DEC_FP__=1 -std=gnu99 -ldfp