Re: [Amforth-devel] Float testing - small/large numbers

[Leon N. M. <leo...@gm...>]

This should now be fixed:

> 1 s>f _pi f* 1000000. d>f f* f>d d.
3141592  ok
> -1 s>f _pi f* 1000000. d>f f* f>d d.
-3141593  ok

the discrepency in the smallest digit is due to the way the fractional part 
gets truncated (it rounds down). If you look directly at the float (take out 
the f>d and convert to binary) they are now idenetical except for the sign 
bit:

01001010001111111011111101100010
11001010001111111011111101100010

It turns out the root cause was something like this:

> -13176795. d2/ d.
-6588398  ok
> 13176795. d2/ d.
6588397  ok

Which is how it should work if you think of division by 2 as shifting right, 
but isn't something I had taken in to account -- a good lesson in how negative 
numbers are represented.

My reposititory has been updated -- keep the tests coming.

-Leon

On Monday, August 30, 2010 04:46:37 pm you wrote:
> Leon,
> 
> I think there is an issue with negative numbers:
> > -1 s>f fconstant _-1    >>>> define 1.0
> 
> ok
> 
> > 1 s>f fconstant _1      >>>> define -1.0
> 
> ok
> 
> > _1 _pi f* _1e4 f* f>s .    >>>> 1.0 * pi * 1.0E4 = 31415
> 
> 31415  ok
> 
> > _-1 _pi f* _1e4 f* f>s .   >>>>> -1.0 * pi * 1.0E4 = -31426
> 
> -31426  ok
> 
> 
> It cannot be caused by of a rounding error accumulating or loosing a
> valid digits. Some minor bug somewhere..
> P.