As an extension, the GNU C compiler supports decimal floating types as defined in the N1312 draft of ISO/IEC WDTR24732. Support for decimal floating types in GCC will evolve as the draft technical report changes. Calling conventions for any target might also change. Not all targets support decimal floating types.
The decimal floating types are
_Decimal128. They use a radix of ten, unlike the floating types
long double whose radix is not
specified by the C standard but is usually two.
Support for decimal floating types includes the arithmetic operators
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types. Use a suffix `df' or
`DF' in a literal constant of type
or `DD' for
_Decimal64, and `dl' or `DL' for
GCC support of decimal float as specified by the draft technical report is incomplete:
__STDC_DEC_FP__to indicate that the implementation conforms to the technical report.
are supported by the DWARF2 debug information format.