Re: it looks like bug:(

[Andrew J. Schorr]

On Thu, Oct 18, 2007 at 09:28:27AM -0700, Micah Cowan wrote:
> Try changing ‘print w’ to ‘printf("%.24g\n", w)’, or just set OFMT to a
> value of "%.24g". OFMT is the conversion specification used to convert
> numbers to strings for output; CONVFMT is used to convert numbers to
> strings when required by an expression.

Actually, the IEEE 754 double-precision floating-point format that gawk
typically uses has about 16 digits of precision, so printing "%.24g" goes well
beyond the actual precision of the floating-point representation.

The easiest way to see the problem is simply to print w-100
instead of printing w:

   bash-3.1$ gawk 'BEGIN{
   > w = 0.0
   > w = w + 0.15
   > w = w + 99.45
   > w = w + 0.4
   > print w-100
   > }'
   1.42109e-14

You can find lots more info on IEEE 754 arithmetic by searching the internet.
Here, for example, is one document that explains the situation:

   http://docs.sun.com/source/806-3568/ncg_math.html

Regards,
Andy