If you compare the actual values by doing "%a" formatting on both the Linux and windows perls, you'll see that 0.1 is exactly the same double.

Your are correct. pack 'd' shows this more definitely.

>perl -E"say sprintf '%vX', pack 'd>', $ARGV[0]" 0.1
3F.B9.99.99.99.99.99.9A
[download]

$ perl -E'say sprintf "%vX", pack "d>", $ARGV[0]', 0.1
3F.B9.99.99.99.99.99.9A
[download]

I believe the OP's activestate perl was built with (mingw port of) gcc

It definitely allows mingw to be used to compile modules, but I don't know if that's what used to build Perl itself. (Update: perl -V hints that it uses mingw)

I beleive Strawberry Perl uses mingw, and I used Strawberry Perl in the test in the earlier post. If so, there are pertinent differences in the libraries between mingw and gcc.

there are pertinent differences in the libraries between mingw and gcc

I think that with mingw, the MS runtime is still used by default for formatting of values.
However, that is avoided (by building with -D__USE_MINGW_ANSI_STDIO) in recent versions of Strawberry Perl, beginning perl-5.26.0.
(Look for "-D__USE_MINGW_ANSI_STDIO" in perl -V:ccflags)

Of course, ActiveState don't build with -D__USE_MINGW_ANSI_STDIO.

Cheers,
Rob

Nope, that doesn't make differences go away, seeing as I was using SP 5.30.2 downloaded and installed less than a week ago. That's newer than 5.26, yet the output was different that the perl built gcc on Unbuntu on WSL on the same machine. The SP build does have -D__USE_MINGW_ANSI_STDIO

Strawberry Perl 5.30.2 on Windows:

>perl -e"CORE::say $^X"
C:\progs\sp5302x64\perl\bin\perl.exe

>perl -v | find "This is"
This is perl 5, version 30, subversion 2 (v5.30.2) built for MSWin32-x
+64-multi-thread

>perl -V:nvsize
nvsize='8';

>perl -V:ccflags
ccflags=' -s -O2 -DWIN32 -DWIN64 -DCONSERVATIVE -D__USE_MINGW_ANSI_STD
+IO -DPERL_TEXTMODE_SCRIPTS -DPERL_IMPLICIT_CONTEXT -DPERL_IMPLICIT_SY
+S -DUSE_PERLIO -fwrapv -fno-strict-aliasing -mms-bitfields';

>perl -e"CORE::say sprintf '%.20g', 0.1"
0.10000000000000000555
[download]

Self-built Perl 5.30.2 on Ubuntu 18.04 LTS on WSL on Windows:

$ uname -a
Linux tribble 4.4.0-18362-Microsoft #476-Microsoft Fri Nov 01 16:53:00
+ PST 2019 x86_64 x86_64 x86_64 GNU/Linux

$ perl -v | grep 'This is'
This is perl 5, version 30, subversion 2 (v5.30.2) built for x86_64-li
+nux-thread-multi

$ perl -V:nvsize
nvsize='8';

$ perl -e'CORE::say sprintf "%.20g", 0.1'
0.10000000000000001
[download]