Re: historical stuff in math(3)

From: Thomas David Rivers <rivers_at_dignus.com>
Date: Thu, 22 Jan 2004 06:56:42 -0500 (EST)
> 
> 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
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Received on Thu Jan 22 2004 - 02:57:40 UTC

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