in reply to Re^7: int() function
in thread int() function
"%.17g" formatting
I was surprised to see 16 digits after the decimal point in a "%.17" notation. Per perl's sprintf docs:
%g a floating-point number, in %e or %f notation
But that's not what actually happens in Perl:
C:>perl -MConfig -le "print +5.3130431399669280e-34; printf qq($_\n), ++5.3130431399669280e-34 for qw/%.17f %.17e %.17g/; print qq($^V\t|\t$ +Config{myuname})" 5.31304313996693e-34 0.00000000000000000 5.31304313996692843e-34 5.3130431399669284e-34 v5.30.0 | Win32 strawberry-perl 5.30.0.1 #1 Thu May 23 12:20:46 +2019 x64
... In this instance, "%.17g" is neither equivalent to "%.17f" (17 digits after the fixed decimal point) nor to "%.17e" (17 digits after the floating decimal point).
I tried on an ancient linux machine with v5.8.5, with similar results:
% perl -MConfig -le 'print +5.3130431399669280e-34; printf qq($_\n), + +5.3130431399669280e-34 for qw/%.17f %.17e %.17g/; print qq($]\t|\t$Co +nfig{myuname})' 5.31304313996693e-34 0.00000000000000000 5.31304313996692843e-34 5.3130431399669284e-34 5.008005 | linux builder4.centos.org 2.6.9-55.0.9.elsmp # +1 smp thu sep 27 18:27:41 edt 2007 i686 i686 i386 gnulinux
The sprintf docs have used that phrasing at least as far back as v5.005 . Am I misunderstanding what I'm seeing? or has perl documentation about %g been wrong for that long?
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Re: TANGENT = %.17g formatting (Re^8:int() function)
by syphilis (Archbishop) on Oct 26, 2020 at 23:57 UTC |
In Section
Seekers of Perl Wisdom