Bug in Floats?

It's just a different printOn: method.  The new one shows the "truth".
 You must now use one of the print formatting methods to display
pretty Floats.

On Wed, Apr 9, 2014 at 10:07 AM, Vaidotas Didžbalis <[hidden email]> wrote:
> 1245 *  0.01 evaluates to 12.45 in Squeak 4.3, but it is
> 12.450000000000001 in later versions.
> regatds,
> Vaidotas
>

2014-04-09 17:53 GMT+02:00 Chris Muller <[hidden email]>:

It's just a different printOn: method.  The new one shows the "truth".
 You must now use one of the print formatting methods to display
pretty Floats.

On Wed, Apr 9, 2014 at 10:07 AM, Vaidotas Didžbalis <[hidden email]> wrote:
> 1245 *  0.01 evaluates to 12.45 in Squeak 4.3, but it is
> 12.450000000000001 in later versions.
> regatds,
> Vaidotas
>

Every two different Float shall have a different printString:
(12.45) = (1245*0.01) -> false.

So...

The printString shall be the shortest decimal that rounds to the same float.

It's hard to demonstrate with a simple snippet, but you can check that we are very close yet:

((Fraction readFrom: '12.450000000000001') - (1245*0.01) asTrueFraction) / (1245*0.01) ulp.

((Fraction readFrom: '12.45') - (1245*0.01) asTrueFraction) / (1245*0.01) ulp.

 

2014-04-09 20:16 GMT+02:00 Nicolas Cellier <[hidden email]>:

2014-04-09 17:53 GMT+02:00 Chris Muller <[hidden email]>:

It's just a different printOn: method.  The new one shows the "truth".
 You must now use one of the print formatting methods to display
pretty Floats.

On Wed, Apr 9, 2014 at 10:07 AM, Vaidotas Didžbalis <[hidden email]> wrote:
> 1245 *  0.01 evaluates to 12.45 in Squeak 4.3, but it is
> 12.450000000000001 in later versions.
> regatds,
> Vaidotas
>

Every two different Float shall have a different printString:
(12.45) = (1245*0.01) -> false.

So...

The printString shall be the shortest decimal that rounds to the same float.

It's hard to demonstrate with a simple snippet, but you can check that we are very close yet:

((Fraction readFrom: '12.450000000000001') - (1245*0.01) asTrueFraction) / (1245*0.01) ulp.

((Fraction readFrom: '12.45') - (1245*0.01) asTrueFraction) / (1245*0.01) ulp.

 

Maybe some other usefull expressions:

((1245*0.01) asTrueFraction printShowingMaxDecimalPlaces: Float precision - Float emin + 1)
-> '12.4500000000000010658141036401502788066864013671875'

"Find least number of decimals necessary for converting back to the same float"

((1 to: Float precision - Float emin + 1) detect: [:i | ((1245*0.01) asTrueFraction roundTo: (10 raisedTo: i) reciprocal) asFloat = (1245*0.01)])
-> 15

"A variant..."

((1 to: Float precision - Float emin + 1) detect: [:i | (((1245*0.01) asTrueFraction roundTo: (10 raisedTo: i) reciprocal) - (1245*0.01) asTrueFraction) abs <= ((1245*0.01) ulp / 2)])
-> 15

((1245*0.01) asTrueFraction printShowingDecimalPlaces: 15)
 '12.450000000000001'