Re: [mv] Sales Tax Calculation

[John Vozza <john@netrom.com>]

On Wed, 15 Sep 1999 mikeh@minivend.com wrote:

> ******    message to minivend-users from mikeh@minivend.com     ******
> 
> Quoting John Vozza (john@netrom.com):
> > 
> > Ryan
> > 
> > Further testing showed that any sales amount that ended with .25 or .75
> > always generated tax that was off by 1 cent. (Using a tax rate of 6%,
> > entered in salestax.asc as .06 or .060 made no difference.)
> > 
> > The error seems to stem from the sprintf used in calculating the tax. I
> > guess Perl is not "rounding" properly. 
> > 
> 
> Operating system? C library in use? Perl uses the standard C libraries
> on your system, and glibc seems to get it right.
> 
> This little script:
> 
> @tries = (.02, .024, .025, .026);
> 
> for(@tries) {
>     print sprintf "round $_ to 2 places: %.2f\n", $_;
> }
> 
> Yields this on Linux/glibc:
> 
> round 0.02 to 2 places: 0.02
> round 0.024 to 2 places: 0.02
> round 0.025 to 2 places: 0.03
> round 0.026 to 2 places: 0.03
> 

Mike

Your script generates the same, correct results on my Linux 2.0.36/libc
Perl 5.004_4 system.

However, a slight mod to your script which is more inline with minivend's
code generates the error.

@tries = (25.24, 25.25, 25.26);

for(@tries) {
$r = $_ * .06;
    print sprintf "round $r to 2 places: %.2f\n", $r;
}


round 1.5144 to 2 places: 1.51
round 1.515 to 2 places: 1.51
round 1.5156 to 2 places: 1.52


Do you think this is a libc vs glibc issue? (Could you try on your system)

My libc=/lib/libc.so.5.4.44

Thanks

John
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