TANGENT = %.17g formatting (Re^8: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
[download]

... 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
[download]

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

%g a floating-point number, in %e or %f notation

 %e    a floating-point number, in scientific notation
 %f    a floating-point number, in fixed decimal notation
 %g    a floating-point number, in %e or %f notation
[download]

 %g    a floating-point number, in scientific notation or fixed decima
+l notation
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