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Re: Float Pt Precision



On Thu, 29 Jul 1999, Uncle George wrote:

> I suppose that this can be chalked up to the extended ( 80bit) precision
> on the Intel box,
> BUT IT MAKES MY life at porting postgres to the alpha, as well as other
> projects very difficult to perform alike equally . A few more
> calculations, and you begin to wonder where the least sig digit has gone
> off to.
> 
> 80 bit extended precision on alpha? This particular feature is not
> mentioned too much ( if at all ) in the alpha literature. Nor are the
> internal methods of processing floating points really described.
> 
> It seems that a lot of folks believe the FP is fast(er than the intel ),
> but it seems to be at the cost of precision. Which for me would be of
> some concern in massive numerical calculations.
> 
> gat
> 
> BTW as a side issue, there doesn't seem to be any way to get the
> compiler to do different 'rounding' techniques.  Ie chopped, +infinity,
> -Infinity.

There was a thread about this on the egcs list (well, a similar issue that
sprang from the IA64 port and 80-bit spills).  It may be interesting
and/or helpful to look at some of the Alpha-ish posts about that issue.
The argument started originally about the -mieee switch being so
necessary and progressed on to precision issues.

C



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