Re: More efficient "dbl_raise"

[Daniel J S. <dan...@ie...>]

Daniel J Sebald wrote:

> gnuplot> print 
> 10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0*10.0 
> - 1e25
> -2147483648.0
> 
> Very strange.  Not concrete proof, but my conjecture about not knowing which is 
> more accurate, outright multiplying via dbl_raise() vs. pow(), does seem a 
> pertinent question.

And this seems to be accurate:

gnuplot> print 
1e25/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10/10 
- 1.0
0.0

Ummmm, so why is the division accurate while the multiplication above appears 
not to be?  Is there something going on with the translation from exponential 
notation and the machine IEEE float representation somewhere around 10^25?

Dan