BUG in Windows Calc [modified]

[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

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[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.

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Hiren Solanki.
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"You will always find me near 127.0.0.1"

[Ennis Ray Lynch Jr]

Not a bug.

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[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.

[peterchen]

How did they?

Agh! Reality! My Archnemesis![^]
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[NPowDev]

However, I thing it hould work in Calc, and fp-precision is not an excuse! I don't have the time to write a .NET application, but... Just a litle test in PowerShell:

PS > write-host ([Math]::Sqrt(4) - 2)
0
PS > write-host ([Math]::Sqrt(4.0) - 2.0)
0
PS > write-host ([Math]::Sqrt([double]4.0) - [double]2.0)
0
PS > write-host ([Math]::Sqrt([single]4.0) - [single]2.0)
0
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0)
0

also to get sure that it is not a convertion issue:

PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("g")
0
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("n")
0.00
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("E")
0.000000E+000
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("G17")
0
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("G")
0
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("n")
0.00
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("n5")
0.00000
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("n17")
0.00000000000000000
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("n57")
0.000000000000000000000000000000000000000000000000000000000
PS > write-host ([Math]::Sqrt([decimal]4.0) - [decimal]2.0).toString("f57")
0.000000000000000000000000000000000000000000000000000000000
PS > write-host ([Math]::Sqrt([single]4.0) - [single]2.0).toString("f55")
0,0000000000000000000000000000000000000000000000000000000
PS > write-host ([Math]::Sqrt([single]4.0) - [single]2.0).toString("f155")
f155
PS > write-host ([Math]::Sqrt([single]4.0) - [single]2.0).toString("f95")
0.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
PS > write-host ([Math]::Sqrt([single]4.0) - [single]2.0).toString("f99")
0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
PS > write-host ([Math]::Sqrt([single]4.0) - [single]2.0).toString("n99")
0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
PS > write-host ([Math]::Sqrt([single]4.0) - [single]2.0).toString("e99")
0.00000000000000000000000000000000000000000000000000000000000

Well... it's a M$ Numpyts! :-D

[Caslen]

Not quite sure what this proves but I hope you had fun doing it! :laugh:

[Juan Pablo G C]

Ja ja, in W2K8 the same -8,1648465955514287168521180122928e-39 :) I think someone forgot clear the stack

Juan Pablo G.C. Overrider Blog