BUG in Windows Calc [modified]

[leppie]

peterchen wrote:

OTOH, the OP failed to notice tha 8e-39 is zero enough when playing around with square roots of 2.

And that is why I cleverly did not point out who the FAILER actually was ;P

((λ (x) `(,x ',x)) '(λ (x) `(,x ',x)))

[QuiJohn]

peterchen wrote:

Actually, Calc internals have been replaced (around XP) with a long numbers library, so it is somehow noteworthy that this isn't enough.

I actually thought I heard it referred to as an "infinite precision" calculator. I've tested it before on values that would make the pre-XP calc choke, but apparently it's not infinite. Ah, googled it... apparently "arbitrary" precision is what it's called. I think MS changed it in the wake of that idiotic, much publicized and ultimately harmless Pentium "floating point" bug. People kept thinking they were finding more bugs, but they were just running into typical floating point inaccuracies.

---

He said, "Boy I'm just old and lonely, But thank you for your concern, Here's wishing you a Happy New Year." I wished him one back in return.

[Dan Neely]

leppie wrote:

Another fails the knowledge about floating point.... When will they ever learn?????

... not until this[^] (What Every Computer Scientist Should Know About Floating-Point Arithmetic) is added to the standard curriculum. :sigh: :sigh:

3x12=36 2x12=24 1x12=12 0x12=18

[Roger Wright]

It's called rounding error, and the problem has been around since computers ran on vacuum tubes. The error has become smaller over the years as bits have been added to operands, but it still occurs due the fact that the finite representation of values which are not, in fact, expressible as a mantissa and a fixed length exponent, can contain a small error. It happens to be very noticeable around zero, but it's present in all FP calculations. It is for that reason programmers have been taught for decades never to use a comparison to zero when the control variable is calcuated using floating point math. It leads to expressions like:

if ((x - k =< 0)|(x + k =< 0))
{
DoSomeThingUsefulBecauseXisZero();
}

The if argument tests for x = 0, +/- k, a constant value. It stumped me when I first saw it in missle guidance test code, until my boss reminded me of what I'd been taught in my only programming class a few years earlier - a bit embarrassing... :-O Have they finally stopped teaching this? :-D

Will Rogers never met me.

[Nish Nishant]

It's still kinda ironic that cheap calculators from 20 years back will still display what the end-user wants to see, while a sophisticated OS comes with a calculator app that thinks it's okay to let its internal workings leak onto the UI.

Regards, Nish

---

My technology blog: voidnish.wordpress.com Code Project Forums : New Posts Monitor This application monitors for new posts in the Code Project forums.

[Lost User]

I still have my first calculator from around 30 years ago, still on its original battery. Still works but takes a good few seconds to respond to each key press. I also still have my alarm clock radio at the side of my bed that I got for my 8th birthday (28 years ago last month). Still keeps and displays perfect time although it is many years since I have tried the alarm or radio out.

Every man can tell how many goats or sheep he possesses, but not how many friends.

[Hiren solanki]

Take a 5 for deep description.

Rating is Always appreciated.
Regards,
Hiren Solanki.
Indian Forum | My Articles | My Profile

---

"You will always find me near 127.0.0.1"

[Ennis Ray Lynch Jr]

Not a bug.

Need custom software developed? I do custom programming based primarily on MS tools with an emphasis on C# development and consulting. I also do Android Programming as I find it a refreshing break from the MS. "And they, since they Were not the one dead, turned to their affairs" -- Robert Frost

[ltj7708]

It appears this will happen with any positive number, if the subtracted value is what should be the square root. For example: click '25' click 'sqrt' click '-' click '5' or click '39.955041' click 'sqrt' click '-' click '6.321' strange...

[wibleywoo]

As expected same error occures with: 9 sqrt - 3 16 sqrt - 4 ...

[ErikKnowles]

Oh geez, this is *not* a bug. Do you have *any* idea of how floating point math is performed? Internal vs. reported precision? You're a programmer??? I'm gobsmacked that this got posted to a code developer site. Oh, and you made CodeProject's daily e-mail, so your ignorance has been transmitted worldwide. Epic fail.

modified on Tuesday, November 2, 2010 4:35 PM

[oconnellc]

Actually, it is accurate. Its problem is that it is *too* precise. If it was a little less precise, it would have decided that it was close enough to zero to just display zero.

[bwallan]

Interesting BUT the Scientific view doesn't have a "sqrt" key; however, the x^y gives the same BUG... bwa

[Plamen Dragiyski]

Woooow, I always use scientific calc in XP and I didn't know it is support sqrt... it seems that they forget to add that button into scientific dialog :laugh:

[Jake Barney]

In this particular instance any answer other than -4 or 0 is inaccurate. Doesn't matter that most of us understand that anything ^-39 power is so small as to be considered zero by most, it's still not zero. Understandably the answer they factored was 1.9999...8164whatever but its funny that the calculator rounded up, then 'forgot' that it did so. Sounds like sloppy programming. What's really funny is change it to the scientific calculator, do 4^.5 power then -2 and it gives a different answer.

[Sasa Cetkovic]

On Windows Server 2008 R2 it gives the first answer in scientific mode, and the second in standard mode.

[David C Thompson]

It works (well, the bug works) with any number. I tried sqrt(25) - 5 and sqrt(9) - :^)

[David C Thompson]

Can you enlighten those of us who may not be as well-informed as you?

[Caslen]

For all you Numptys who this this is a bug - you can easily prove that it isn't, follow these simple steps:- 1. Convert the number 4 to a binary floating point representation and write it down. 2. Continue with your pen and paper and using a suitably selected algorithm to calculate the square root of a number presented in binary floating point form work out the square root of the binary floating point representation of the number 4 found in step 1. 3. Convert the number 2 into a binary floating point form (preferably the same form as that used in step 1) 4. Perform a floating point binary subtract on the result of step 3 from the result of step 4. 5. Do you have zero? No you do not!

[Michael Kingsford Gray]

It needs to do it like HP calculators have always done.