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----- Original Message ----- From: "Neil Carlson" <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, March 31, 2004 2:38 PM Subject: Re: configurable default real > On Wed, 2004-03-31 at 15:29, Robin wrote: > > > Date: Tue, 30 Mar 2004 23:58:55 -0500 (EST) > > > From: [log in to unmask] > > > It would be a great convenience for such users if there were a "standard" > > > means of interfacing to a generic binary computer, with two's complement > > > integers, byte sized characters, 16, 32, and 64 bit integers and logicals, 32, 64, and > > > 128(?) > > > > 80 is a common size. > > Not really, is it? x86 processors have internal 80 bit fp registers > but anything that has to go out to memory gets truncated to 64 bits. > Since a high-level like Fortran can't/shouldn't make assumptions > about where in the system a fp value is, an 80 bit kind really isn't > feasible here. Are there systems that actually support 80 bit fp > numbers fully? gcc supports 80 bit floating point numbers, on most platforms with appropriate hardware. So do most commercial C compilers which attempt any degree of gcc compatibility. This includes saving to memory in that format (along with 16 to 48 wasted bits). Nothing prevents Fortran from doing the same on the same platforms, except practicality. Fortran has more satisfactory syntax support than C, e.g. selected_real_kind(18), unless you prefer the C scheme of silently dropping back to double when deemed more practical. The trend is away from supporting extended double, as the "64-bit" Windows for 32-bit extended architectures doesn't even permit use of the extended registers, and hardware support for vector is generally restricted to 32- and 64-bit formats.