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I am surprised with behaviour of awk while performing floating point calculations. It lead me to wrong calculation on table data. 

$ awk 'BEGIN {print 2.3/0.1}'
23  <-- Ok
$ awk 'BEGIN {print int(2.3/0.1)}'
22  <-- Wrong!

$ awk 'BEGIN {print 2.3-2.2==0.1}'
0   <-- Surprise!
$ awk 'BEGIN {print 2.3-2.2>0.1}'  <-- Din't produce any output :(
$ awk 'BEGIN {print 2.3-2.2<0.1}'
1   <-- Totally confused now ...

Can somebody throw light as to what's happing here?

EDIT 1

As pointed by @fedorqui, output of second last command goes to file named 0.1 because of redirection operator (>).

Then how am I supposed to perform greater than (>) operation?

Solution to it is also given by @fedorqui

$ awk 'BEGIN {print (2.3-2.2>0.1)}'
0  <-- Wrong!
jkshah
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    +1 for interesting question. I found some info --> http://www.gnu.org/software/gawk/manual/html_node/Floating-Point-Issues.html Note also that `awk 'BEGIN {print 2.3-2.2>0.1}'` writes the result of `2.3-2.2` in a file with `0.1` name. – fedorqui Oct 29 '13 at 11:12
  • @fedorqui I also searched on this topic. All they say is expect unexpected behaviour! How am I supposed to solve my problem accurately? I tried solving in `perl` but unfortunately it also misbehaves, may be in different way. – jkshah Oct 29 '13 at 11:17
  • @fedorqui thanks for pointing that out. I have updated question with addition query! – jkshah Oct 29 '13 at 11:25
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    For this I guess the solution is to do `awk 'BEGIN {print (2.3-2.2>0.1)}'`. For the rest, I am still checking, it is a juicy topic. – fedorqui Oct 29 '13 at 12:34

1 Answers1

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The following section from the manual should help you understand the issue you're observing:

15.1.1.2 Floating Point Numbers Are Not Abstract Numbers

Unlike numbers in the abstract sense (such as what you studied in high school or college arithmetic), numbers stored in computers are limited in certain ways. They cannot represent an infinite number of digits, nor can they always represent things exactly. In particular, floating-point numbers cannot always represent values exactly. Here is an example:

 $ awk '{ printf("%010d\n", $1 * 100) }'
 515.79
 -| 0000051579
 515.80
 -| 0000051579
 515.81
 -| 0000051580
 515.82
 -| 0000051582
 Ctrl-d

This shows that some values can be represented exactly, whereas others are only approximated. This is not a “bug” in awk, but simply an artifact of how computers represent numbers.

A highly recommended reading:

What every computer scientist should know about floating-point arithmetic

devnull
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