quadruple precision (e.g. on SPARC). As of gcc 4.3, a quadruple precision is also supported on x86, but as the nonstandard type __float128 rather than long double. Although the x86 architecture, and specifically the x87 floating-point instructions on x86, supports 80-bit extended-precision operations, it is possible to configure the processor to automatically round operations to double (or even single) precision. Conversely, in extended-precision mode, extended precision may be used for intermediate compiler-generated calculations even when the final results are stored at a lower precision (i.e. FLT_EVAL_METHOD == 2). With gcc on Linux, 80-bit extended precision is the default; on several BSD operating systems (FreeBSD and OpenBSD), double-precision mode is the default, and long double operations are effectively reduced to double precision. (NetBSD 7.0 and later, however, defaults to 80-bit extended precision ). However, it is possible to override this within an individual program via the FLDCW "floating-point load control-word" instruction. On x86_64, the BSDs default to 80-bit extended precision. Microsoft Windows with Visual C++ also sets the processor in double-precision mode by default, but this can again be overridden within an individual program (e.g. by the _controlfp_s function in Visual C++). The Intel C++ Compiler for x86, on the other hand, enables extended-precision mode by default. On IA-32 OS X, long double is 80-bit extended precision. Other specifications In CORBA (from specification of 3.0, which uses "ANSI/IEEE Standard 754-1985" as its reference), "the long double data type represents an IEEE double-extended floating-point number, which has an exponent of at least 15 bits in length and a signed fraction of at least 64 bits", with GIOP/IIOP CDR, whose floating-point types "exactly follow the IEEE standard formats for floating point numbers", marshalling this as what seems to be IEEE 754-2008 binary128 a.k.a. quadruple precision without using that name. See also Quadruple precision Extended precision References Computer arithmetic Data types C (programming language)