Re2: IEEE double extended form

[Turkowski, Ken]

I agree. 23 bits of exponent is overkill. Precision is more useful than range.
 
"Doubled precision" ends up wasting an exponent's worth of bits, but is
straightforward to compute, as shown in Linnainmaa's TOMS v.7,n.3, 9/81 paper.
 
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From: validgh!dghaSun.COM (David G. Hough on validgh)
Subject: Re: IEEE double extended forma
 
>     1 bit for the sign
>    15 bits for the exponent, bias of +16383
>   112 bits for the fraction
 
This is the "quad" format specified in the SPARC and PA-RISC instruction
set architectures, and possibly others.
 
> "Data Formats optimized for Scalable Coherent Interface Processors":
>   1 sign
>  23 exponent, bias of +4194303
> 104 mantissa
 
> Any ideas on what name to call this in "C"?
 
"A mistake!"   I don't know any benefit to having such a large exponent
range.   It merely postpones the moment of reckoning when a wildly divergent
computation finally starts to produce exceptions.
 
The most significant alternative to either SPARC/PARISC quad or
x86/68k extended is "doubled precision" quad from RS/6000 or PowerPC.
Two doubles are used to represent quadruple precision with no increase in
exponent range.   The only merit in this approach is that it is relatively
cheap in software if fused multiply-add is available in double precision.