Thank you for your explanation both of you.
> alester@flr4[~/play]$ perl sprintf.pl
> 056 56.9928946
>
> ...
>
> In general, the chances that you've found a bug in the language or
> implementation that's been around as long and is as widely used as Perl
> 5.6 is preeetty small.
I know that !
That's why I didn't understand this behaviour first. Perl has been around
since 13 years and during past years I've already found a few
workarounds about bad calculations due to roundings.
I imagine that such a discussion occured in 80's.
But this one is different, behaviour is not equally distributed amongst
input values. I'm very puzzling with that.
I know that roundings are often tricky from language to language (Javascript
has not the same rules for example and a small solid state calculator has
different ones also).
But you must know that it's very difficult to write a portable code from
langage to langage when rules are different.
And in Perl I found these rules not very consistent.
Can you tell me what you are thinking of that ?
^
perl -e '$a=0.79; printf sprintf("%03d %30.29f", $a*100, $a*100);'
079 79.0
perl -e '$a=0.69; printf sprintf("%03d %30.29f", $a*100, $a*100);'
069 69.0
perl -e '$a=0.49; printf sprintf("%03d %30.29f", $a*100, $a*100);'
049 49.0
perl -e '$a=0.55; printf sprintf("%03d %30.29f", $a*100, $a*100);'
055 55.00710542735760100
perl -e '$a=0.59; printf sprintf("%03d %30.29f", $a*100, $a*100);'
059 59.0
perl -e '$a=0.56; printf sprintf("%03d %30.29f", $a*100, $a*100);'
056 56.00710542735760100
perl -e '$a=0.61; printf sprintf("%03d %30.29f", $a*100, $a*100);'
061 61.0
perl -e '$a=0.65; printf sprintf("%03d %30.29f", $a*100, $a*100);'
065 65.0
perl -e '$a=0.66; printf sprintf("%03d %30.29f", $a*100, $a*100);'
066 66.0
perl -e '$a=0.68; printf sprintf("%03d %30.29f", $a*100, $a*100);'
068 68.0
perl -e '$a=0.28; printf sprintf("%03d %30.29f", $a*100, $a*100);'
028 28.00355271367880050
perl -e '$a=0.27; printf sprintf("%03d %30.29f", $a*100, $a*100);'
027 27.0
perl -e '$a=0.26; printf sprintf("%03d %30.29f", $a*100, $a*100);'
026 26.0
perl -e '$a=0.24; printf sprintf("%03d %30.29f", $a*100, $a*100);'
024 24.0
perl -e '$a=0.47; printf sprintf("%03d %30.29f", $a*100, $a*100);'
047 47.0
perl -e '$a=0.33; printf sprintf("%03d %30.29f", $a*100, $a*100);'
033 33.0
perl -e '$a=0.17; printf sprintf("%03d %30.29f", $a*100, $a*100);'
017 17.0
And if you try a loop, it works too, since, for perl, 0.01+0.01 > 0.02
and so on.
But if I take my calculator :
0.57*100 = 57 exactly !
Example :
perl -e 'for ($a=0.01;$a<1;$a+=0.01) { print sprintf("%20.19f %03d
%20.19f\n", $a, $a*100, $a*100);} '
0.012 001 1.000
0.024 002 2.000
0.0299989 003 3.000
0.048 004 4.000
0.0500028 005 5.000
0.0600047 006 6.0008882
0.0700067 007 7.0008882
0.0800017 008 8.000
0.0899967 009 9.000
0.017 010 10.000
0.1099867 010 10.9982236
0.1199817 011 11.9982236
0.1299767 012 12.9982236
0.1399856 013 13.9982236
0.1499944 015 15.000
0.1600033 016 16.000
0.1700122 017 17.000
0.1800211 018 18.0035527
0.1900300 019 19.0035527
0.2000389 020 20.0035527
0.2100477 021 21.0035527
0.2200566 022 22.0071054
0.2300655 023 23.0071054
0.2400744 024 24.0071054
0.2500555 025 25.0071054
0.2600644 026 26.0071054
0.2700733 027 27.0071054
0.2800822 028 28.0071054
0.2900910 029 29.0106581
0.3000999 030 30.0106581
0.3101088 031 31.0106581
0.3201177 032 32.0142109
0.3301266 033 33.0142109
0.3401354 034 34.0142109
0.3501443 035 35.0142109
0.3601532 036 36.0142109
0.3701621 037 37.
