> > On Wed, Jan 21, 2004 at 06:41:49AM -0500, Thomas David Rivers wrote: > >> Isn't all the vax-D format related stuff math(3) getting pretty old ? > > > > It's very similar to the IBM mainframe format. So, a port > > of FreeBSD to the IBM mainframe could still use it. (The VAX > > format was just a copy of the IBM one with an extra precision bit > > thrown in every now-and-then.) > > Not really. The IBM S/360 uses base-16 whereas virtually everyone > else (including VAX) uses binary. The S/360 double precision format > has a 14-digit (56-bit) fraction (no implicit digit), a fraction sign > and a 7-bit signed exponent. The VAX-D documentation in math(3) is > totally irrelevant to the S/360. Any serious math library would need > significant re-work to handle the increased range and reduced/variable > precision. My bad... I thought the VAX code was base-16 as well. I could be confusing it with the Data General MV series... > > Someone else mentioned the Alpha - VAX-format FP is specified in > the architecture to simplify migration from the VAX. The early chips > included it in hardware - do the recent chips still include it? > > > But - even the mainframe has an available/alternate IEEE format now, > > and the mainframe version of gcc uses that... > > I think this must be new in the S/390. It's definitely not part of > the S/360 or S/370 families and I don't believe it existed on the 30xx > or 43xx families. Yes - new will ALS 1 (Architectural Level Set #1). If your OS/390 operating system is new enough (past 1992 I think?), it will emulate the new IEEE instructions if your hardware doesn't have them. Linux will do the same thing. The mainframe has evolved quite a lot since the 360. The new z/Series machines are serious 64-bit Linux contenders. But - I'm getting off-topic... - Dave R. - -- rivers_at_dignus.com Work: (919) 676-0847 Get your mainframe programming tools at http://www.dignus.comReceived on Thu Jan 22 2004 - 02:57:40 UTC
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