I see your point but how likely will a 999....9. sort of situation
occur? Drop 1 digit and the result will be 1e15. which is perfectly
satisfactory. The problem is that when you push the limits of the size
of a floating point number, the result is within the the tolerance level
for 'close enough" to integer to be treated as one. This is inherent in
APL and J and was done for a purpose. -the number of digits of a float
will be less than for an integer because the float requires an exponent
as well as a mantissa while then integer doesn't need the exponent. A
32bit word could hold a 31 bit number while a float with an 8 bit
exponent would hold a 23 bit number
r=:1.0000000000000009
r=1
1
r-1
8.88178e_16
r=:1.00000000000000009
r=1
1
r-1
0
least significant bits lost because there is no room for them. in
99.9999+ % of cases this is not a problem.
Don Kelly
On 2017-08-11 2:11 AM, Henry Rich wrote:
The error, methinks, is that 999...9. is rounded to integer and then
reported as integer. It should keep floating type.
Bit-twisting code needs to be sure that no bits have been lost. Integral
type should be a guarantee of that. Floats that have values
unrepresentable accurately should not be automatically called ints.
Henry Rich
On Aug 11, 2017 06:14, "Don Kelly" <[email protected]> wrote:
isn't an advantage of APL and J that the person writing a
program/app/whatever, doesn't have to deal with the distinctions between
integer and damn near integer within the limitations of the computer
binary resolution?. In most cases this isa good thing because close enough
-given the +/- of data input is sufficient for the idiot box to decide. J
moves away from C/C++/ and other languages which often seem to be
emphasizing stuff that Iverson tried to eliminate in APL and J . Muh of
that stuff is something that can be handled by the idiot box so that:
Problem-->basic analysis--. coding that fits the analysis rather than the
details( users aim at the essentials rather than the details- "/I want the
answer and I dont care about what is involved in the background of %,*
*/
The discussion below deals with representation of numeric values being
floating point or integer when pushing the limits-IS IT IMPORTANT IN THE
REAL WORLD unless you have a Cray in the back bedroom?
Old fart expressing opinions
Don Kelly
On 2017-08-10 6:27 PM, Bill wrote:
I suspect J interpreter didn't has the knowledge that the original string
had been 9999999999999999.3
with .3 because what J saw was the floating point result of parsing by c
library. Ieee floating point has 15 to 16 significant digits so that 1e16
and 1e16-1 is the same number.
Perhaps one could use long double to parse number on J64.
Sent from my iPhone
On 10 Aug, 2017, at 3:48 AM, Henry Rich <[email protected]> wrote:
Quite right.
Henry Rich
On Aug 9, 2017 20:46, "Raul Miller" <[email protected]> wrote:
Well, since it's encoded as an integer (which I would have noticed if
I had read Bob Therriault's original post more closely), and not [like
I was thinking] a float, I agree that dropping the .3 is better than
adding a 1.
That said, I guess we also should not object too loudly if
9999999999999999.3 were instead encoded the same as
9999999999999999+0.3 gets encoded.
Thanks,
--
Raul
On Wed, Aug 9, 2017 at 3:25 PM, Henry Rich <[email protected]> wrote:
Surely integer 999...9 is a better value than 1000...0 .
Henry Rich
On Aug 9, 2017 18:33, "Raul Miller" <[email protected]> wrote:
It's not a bug, it's an artifact of the 64 bit floating point standard.
2 ^.9999999999999999
53.1508
https://en.wikipedia.org/wiki/IEEE_754#Basic_and_interchange_formats
The binary64 format has 53 binary digits or 15.95 decimal digits. This
means ".16#'9' cannot be represented exactly using this format.
And, we do not use exact representation of large numbers by default
because that's too slow for large datasets. Put differently, if you
want exact representation and are willing to take the performance hit,
you should specify that. For example: ".'x',~16#'9' or
".'3r10+','x',~16#'9'
Thanks,
--
Raul
On Wed, Aug 9, 2017 at 12:05 PM, Henry Rich <[email protected]>
wrote:
This is a bug, since 999...9.3 should become 999...9 rather than
100...0.
I'm away from home now, but I think what's happening is this:
999...9 is converted to integer
. is encountered and turns it to float
It's rounded to the nearest float which is 100...0
As a final step the JE checks to see if the value is exactly integral,
which it is, and it is converted back to integer.
If you add this to Interpreter/Bugs I'll fix it when i get back.
Henry Rich
On Aug 9, 2017 16:16, "bill lam" <[email protected]> wrote:
I think this is the difference between 32 and 64-bit,
9!:14''
j602/2008-03-03/16:45
3!:0[ 9999999999999999.3
4
In J32
a.i. 2 fc 9999999999999999.3
0 128 224 55 121 195 65 67
a.i. 2 fc 1e16
0 128 224 55 121 195 65 67
the number has the same bit pattern as 1e16 (an integer)
which can be represented as a 64-bit integer. I guess
J64 is correct since 9999999999999999.3 and 1e16 is the
same number in ieee fp and J prefers integer to floats,
eg
3!:0 [ 2.0
4
Ср, 09 авг 2017, robert therriault написал(а):
Hi Pascal,
I see the same behaviour in j806 as j805. Do you see something
different?
JVERSION
Engine: j806/j64avx/darwin
Beta-4: commercial/2017-06-27T12:55:06
Library: 8.06.03
Qt IDE: 1.5.3/5.6.2
Platform: Darwin 64
Installer: J806 install
InstallPath: /users/bobtherriault/j64-806
Contact: www.jsoftware.com
(; datatype) 999999999999999.3
┌────┬────────┐
│1e15│floating│
└────┴────────┘
(; datatype) 9999999999999999.3
┌─────────────────┬───────┐
│10000000000000000│integer│
└─────────────────┴───────┘
(; datatype) 99999999999999999.3
┌──────────────────┬───────┐
│100000000000000000│integer│
└──────────────────┴───────┘
(; datatype) 999999999999999999.3
┌───────────────────┬───────┐
│1000000000000000000│integer│
└───────────────────┴───────┘
(; datatype) 9999999999999999999.3
┌────┬────────┐
│1e19│floating│
└────┴────────┘
Cheers, bob
On Aug 9, 2017, at 7:54 AM, 'Pascal Jasmin' via Programming <
[email protected]> wrote:
in j806, 9999999999999999.310000000000000000 probably the j805
behaviour is preferred. If only for consistency. But there may be a
good
reason for change.
From: robert therriault <[email protected]>
To: Programming forum <[email protected]>
Sent: Wednesday, August 9, 2017 10:40 AM
Subject: [Jprogramming] Integer-floating type change for large
numbers
in j805 and j806
I am guessing that the following has something to do with
precision of
large numbers in j805 and is also true for j806.
(; datatype) 999999999999999.3
┌────┬────────┐
│1e15│floating│
└────┴────────┘
(; datatype) 9999999999999999.3
┌─────────────────┬───────┐
│10000000000000000│integer│
└─────────────────┴───────┘
(; datatype) 99999999999999999.3
┌──────────────────┬───────┐
│100000000000000000│integer│
└──────────────────┴───────┘
(; datatype) 999999999999999999.3
┌───────────────────┬───────┐
│1000000000000000000│integer│
└───────────────────┴───────┘
(; datatype) 9999999999999999999.3
┌────┬────────┐
│1e19│floating│
└────┴────────┘
JVERSION
Engine: j805/j64/darwin
Release: commercial/2016-12-11T08:17:56
Library: 8.05.14
Qt IDE: 1.5.4/5.6.2
Platform: Darwin 64
Installer: J805 install
InstallPath: /applications/j64-805
Contact: www.jsoftware.com
Further investigation shows me it was not this way with the 32 bit
version of j701, so it may be an artifact of moving to 64 bit?
(; datatype) 999999999999999.3
┌────┬────────┐
│1e15│floating│
└────┴────────┘
(; datatype) 9999999999999999.3
┌────┬────────┐
│1e16│floating│
└────┴────────┘
(; datatype) 999999999999999999.3
┌────┬────────┐
│1e18│floating│
└────┴────────┘
(; datatype) 9999999999999999999.3
┌────┬────────┐
│1e19│floating│
└────┴────────┘
JVERSION
Engine: j701/2011-01-10/11:25
Library: 7.01.088
Platform: Darwin 32
Installer: j701a_mac_intel.dmg
InstallPath: /Applications/j701
Cheers, bob
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