Να και η εξήγηση…

This item ran on the Joel on Software homepage on Wednesday, September 26, 2007

By now you’ve probably seen a lot of the brouhaha over a bug in the newest version of Excel, 2007. Basically, multiplying 77.1*850, which should give you 65,535, was actually displaying 100,000.

Before I try to explain this, I should disclose that I did work on the Excel team, but that was thirteen years ago. I haven’t been there for a long time. I don’t even think I know anyone on that team any more. I’m just trying to explain the bug a little bit as a public service.

The first thing you have to understand is that Excel keeps numbers, internally, in a binary format, but displays them as strings. For example, when you type 77.1, Excel stores this internally using 64 bits:

0100 0000 0101 0011 0100 0110 0110 0110
0110 0110 0110 0110 0110 0110 0110 0110

The display is showing you four characters: “7”, “7”, “.”, and “1”.

Somewhere inside Excel is a function that converts binary numbers to strings for displaying. This is the code that has the bug that causes a few numbers which are extremely close to 65,535 to be formatted incorrectly as 100,000.

If you use the number further along in calculations, for example, if you add 2 to the results, you’ll get the right thing.

=77.1*850 -> displays 100000

=77.1*850+2 -> displays 65537, correctly.

Just to throw people off, this bug also exists for a few numbers which are extremely close to 65,536. They display incorrectly as 100,001.

=77.1*850+1 -> displays 100,001, incorrectly.

This is still only a bug in the number formatting code; if you try to make a chart with that number in it, you’ll get a correct chart. Διαβάστε όλο το άρθρο »

Calculation Issue Update

Yesterday we were alerted to an issue in Excel 2007 (and Excel Services 2007) involving calculation of numbers around 65,535. The Excel team would like to provide a description of the issue and explain what we’re doing about it.

Background
Yesterday evening we were alerted to an issue in Excel 2007 (and Excel Services 2007) involving calculation of numbers around 65,535. The first example that we heard about was =77.1*850, but it became clear from our testing as well as additional reports that this was just one instance where Excel 2007 would return a value of 100,000 instead of 65,535. The majority of these additional reports were focused on multiplication (ex. =5.1*12850; =10.2*6425; =20.4*3212.5 ), but our testing showed that this really didn’t have anything do to with multiplication – it manifested itself with many but not all calculations in Excel that should have resulted in 65,535 (=65535*1 and =16383.75*4 worked for instance). Further testing showed a similar phenomenon with 65,536 as well. This issue only exists in Excel 2007, not previous versions. Διαβάστε όλο το άρθρο »

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