Re: [Bug-apl] number precision in saved workspaces

[Xiao-Yong Jin]

Hi Jürgen,

Thanks.  I found more floating point reproduction issues.

      ⎕PP←17
      x-y←x←○3 4
0 0
      x-⍎⍕x
0 1.7763568394002505E¯15
      x-¯14⎕CR 14⎕CR x
0 0
      2⎕TF 2⎕TF ‘y'
y
      y
9.4247779607693793 12.566370614359172
      x
9.4247779607693793 12.566370614359172
      x-○3 4
0 0
      y-○3 4
0 ¯1.7763568394002505E¯15
      x-y
0 1.7763568394002505E¯15
      9.4247779607693793 12.566370614359172-○3 4
0 ¯1.7763568394002505E¯15


The exact representation by 14⎕CR works great (as in one of the ISO CF 
implementations), but both ⎕TF and ⍎⍕ fail to reproduce the exact number.

Since you last change, the )save )load does keep the exact values, and I looked 
at the saved workspace file, the numbers are
146   <Ravel vid="1" cells="⁴9.4247779607693793⁴12.566370614359171"/>
147   <Ravel vid="2" cells="⁴9.4247779607693793⁴12.566370614359172"/>
185     <Symbol name="x" stack-size="1">
186       <Variable vid="2"/>
187     </Symbol>
188 
189     <Symbol name="y" stack-size="1">
190       <Variable vid="1"/>
191     </Symbol>
Here, the last digit of y is 1 instead of 2, as shown in the REPL.

So it seems the routine used to format numbers has some problem with the last 
digits, even if with ⎕PP=17?  Or it’s just the reader has some problem?

In addition, )dump and )out still changes the floating point number, but 
perhaps that is the same issue as in ⎕TF and ⍎⍕?

> On Jun 7, 2016, at 3:29 PM, Juergen Sauermann <address@hidden> wrote:
> 
> Hi Xiao-Yong,
> 
> OK - SVN 739.
> 
> /// Jürgen
> 
> 
> On 06/07/2016 08:16 PM, Xiao-Yong Jin wrote:
>> Hi Jürgen,
>> 
>> Thanks, though the current behavior still does not give the exact number bit 
>> by bit.  Can you change it to %.17g, or 
>> std::numeric_limits<double>::max_digits10?
>> 
>> In addition, is it OK to raise the maximum allowed ⎕PP to 17?
>> 
>> Best,
>> Xiao-Yong
>> 
>> 
>>> On Jun 7, 2016, at 12:37 PM, Juergen Sauermann <address@hidden>
>>>  wrote:
>>> 
>>> Hi Xiao-Yong,
>>> 
>>> thanks, fixed in SVN 738.
>>> 
>>> /// Jürgen
>>> 
>>> 
>>> On 06/07/2016 08:13 AM, Xiao-Yong Jin wrote:
>>> 
>>>> Hello,
>>>> 
>>>> Is the following behavior intended?  Note the x value after load.
>>>> 
>>>>       )clear
>>>> CLEAR WS
>>>>       x←.12345678901234567890
>>>>       ⎕pp←16
>>>>       x
>>>> 0.1234567890123457
>>>>       )wsid tmp
>>>> WAS CLEAR WS
>>>>       )save tmp
>>>> 2016-06-07  01:09:15 (GMT-5)
>>>>       )clear
>>>> CLEAR WS
>>>>       )load tmp
>>>> SAVED 2016-06-07 01:09:15 (GMT-5)
>>>>       x
>>>> 0.123457
>>>>       ⎕pp
>>>> 16
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>> 
>