Re: pack() returns an unusable string

G'day Rob,

I'm not sure if this helps, but it seems to reproduce what you're describing on a different platform: Cygwin 3.2.0 on Win10. I kept most of your posted code as is; I added some info up front; and, I looped through all of the templates on both 5.32 and 5.34.

$ cat pm_11133064_pack_test.pl
use warnings;

print "OS: $^O; Perl: $^V;\n",
    `perl -V:usequadmath`, `perl -V:nvtype`, "\n";

my @templates = qw{d d< d> D D< D>};

for $template (@templates) {
    print "TEMPLATE: $template\n";
    $nv = 2.4;
    $p = pack $template, $nv;
    $s = "'$p'";

    system $^X, '-wle', "print unpack('H*', $s);";
}
[download]

$ perl pm_11133064_pack_test.pl
OS: cygwin; Perl: v5.32.0;
usequadmath='undef';
nvtype='double';

TEMPLATE: d
3333333333330340
TEMPLATE: d<
3333333333330340
TEMPLATE: d>
4003333333333333
TEMPLATE: D
Invalid type 'D' in pack at pm_11133064_pack_test.pl line 11.
[download]

$ perl pm_11133064_pack_test.pl
OS: cygwin; Perl: v5.34.0;
usequadmath='undef';
nvtype='double';

TEMPLATE: d
3333333333330340
TEMPLATE: d<
3333333333330340
TEMPLATE: d>
4003333333333333
TEMPLATE: D
Can't find string terminator "'" anywhere before EOF at -e line 1.
TEMPLATE: D<
Can't find string terminator "'" anywhere before EOF at -e line 1.
TEMPLATE: D>
Can't find string terminator "'" anywhere before EOF at -e line 1.
[download]

— Ken

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Re^2: pack() returns an unusable string by syphilis (Archbishop) on May 27, 2021 at 13:50 UTC
I'm not sure if this helps ... Heh ... it helps ... but only in that it reaffirms what I already knew ;-) I'll elaborate a little on how this all came about. As I mentioned in the opening post, with perl-5.34.0, pack's 'D' templates are allowed on all builds irrespective of whether $Config{nvtype} is 'double' or 'long double' or '__float128'. In earlier perl versions the 'D' templates were supported only if $Config{nvtype} was 'long double'. With perl-5.34.0 and nvtype of 'long double' we get: `C:\>perl -wle "print unpack 'H', pack 'D', 2.4;" 9a999999999999990040000000000000` [download] whereas with perl-5.34.0 and nvtype of double, the same command yields a slightly different result: `C:\>perl -wle "print unpack 'H', pack 'D', 2.4;" 00989999999999990040000000000000` [download] That's pretty much as I expected because the string being unpacked in the first one-liner is different to the string being unpacked in the second one-liner. But then I wanted to see what the result would be if the string created on the long double build (in the first one-liner) was fed to the 'double' build (in the second one-liner). Would the result be 9a999999999999990040000000000000 or 00989999999999990040000000000000 ? (I was quite sure it would be the former, but I knew that if I didn't check then I'd get it wrong.) So I thought I'd do something cute: I decided that, on my 'long double' build, I would run the following script: `use warnings; $template = 'D<'; $nv = 2.4; $p = pack $template, $nv; $s = "'$p'"; # Now pass $p to the 'double' build of perl. $double_perl = "C:/perl-5.34.0/bin/MSWin32-x64-multi-thread/perl.exe"; system $double_perl, '-wle', "print unpack('H', $s);";` [download] But, as already demonstrated, that doesn't DWIM. In the end, I took the clunky approach of running 2 scripts. Firstly, on the 'long double' build of perl-5.34.0 I ran the following script that would print the string returned by pack() to a file: `use warnings; $p = pack("D", 2.4); open WR, '>', 'packstr.txt' or die "Opening: $!"; binmode(WR); print WR $p; close WR or die "Closing: $!";` [download] Then, on the 'double' build of perl-5.34.0, I ran a script that passed the string that was saved in packstr.txt to unpack(): `use warnings; open RD, '<', 'packstr.txt' or die "Opening: $!"; binmode(RD); $p = <RD>; close RD or die "Closing: $!"; print unpack("H", $p);` [download] That script output 9a999999999999990040000000000000. (Hmph ... as if it was ever going to do anything else ...) It just would have been so much cleaner and simpler if I could have got the first approach to work. Cheers, Rob	[reply] [d/l] [select]

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Re^2: pack() returns an unusable string
by syphilis (Archbishop) on May 27, 2021 at 13:50 UTC

I'm not sure if this helps ...

C:\>perl -wle "print unpack 'H*', pack 'D', 2.4;"
9a999999999999990040000000000000
[download]

C:\>perl -wle "print unpack 'H*', pack 'D', 2.4;"
00989999999999990040000000000000
[download]

use warnings;

$template = 'D<';
$nv = 2.4;
$p = pack $template, $nv;

$s = "'$p'";

# Now pass $p to the 'double' build of perl.
$double_perl = "C:/perl-5.34.0/bin/MSWin32-x64-multi-thread/perl.exe";
system $double_perl, '-wle', "print unpack('H*', $s);";
[download]

use warnings;

$p = pack("D", 2.4);

open WR, '>', 'packstr.txt' or die "Opening: $!";
binmode(WR);
print WR $p;
close WR or die "Closing: $!";
[download]

use warnings;

open RD, '<', 'packstr.txt' or die "Opening: $!";
binmode(RD);
$p = <RD>;
close RD or die "Closing: $!";

print unpack("H*", $p);
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