Re: pack/unpack woes

Win8 Strawberry 5.30.3.1 (64)  Tue 06/14/2022 17:01:38
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

use Data::Dump qw/dd pp/;

my $ogg_head = pack 'H*',
    '4F6767530002000000000000000083CA3DC0000000009F59730A0113';
dd $ogg_head;  # for debug

my ($ogg_magic, $opus_version, $flags, $granule_position,
    $serial_number, $sequence_number, $checksum, $total_segments,
    $segment_size) =
  # unpack('C4 C1 C1 C8 C4 C4 C4 C1 C1', $buf);
    unpack('a4 C C Q N N N C C', $ogg_head);
print "'$ogg_magic' \n";

dd $ogg_magic, $opus_version, $flags, $granule_position,
   $serial_number, $sequence_number, $checksum, $total_segments,
   $segment_size;

printf "%s %02x %02x %08x %04x %04x %04x %02x %02x \n",
       $ogg_magic, $opus_version, $flags, $granule_position,
       $serial_number, $sequence_number, $checksum, $total_segments,
       $segment_size;

^Z
pack("H*","4f6767530002000000000000000083ca3dc0000000009f59730a0113")
'OggS'
("OggS", 0, 2, 0, 2211069376, 0, 2673439498, 1, 19)
OggS 00 02 00000000 83ca3dc0 0000 9f59730a 01 13
[download]

Note: Check that your version of Perl supports the Q pack/unpack template specifier.

Give a man a fish: <%-{-{-{-<

Comment on Re: pack/unpack woes Select or Download Code

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Re^2: pack/unpack woes by ikegami (Patriarch) on Jun 14, 2022 at 21:31 UTC
A little explanation of the changes, with some corrections: `C4` is the same as `C C C C`. It extracts 4 numbers. `$ perl -e'printf "0x%X\n", $_ for unpack "C4", "\x12\x34\x56\x78"' 0x12 0x34 0x56 0x78` [download] But that's not what you want. You want to extract a single 32-bit unsigned integer in little-endian byte order.^[1] After consulting Mini-Tutorial: Formats for Packing and Unpacking Numbers, we determine that we need `L<` or `V` for that. `$ perl -e'printf "0x%X\n", $_ for unpack "L<", "\x12\x34\x56\x78"' 0x78563412` [download] So, what you want is `unpack( 'a4 C C Q< L< L< L< C', $ogg_head )` [download] Note that this is only 27 bytes, not 28. The number of remaining bytes is indicated by that last field (the 27th byte), and may be a number other than one. As hinted by the parent, `Q` is only available on builds of Perl with 64-bit integers (i.e. where `perl -V:uvsize` aka `perl -Mv5.10 -MConfig -e'say $Config{uvsize}'` prints 8 or more). The parent assumed big-endian order and thus used `N`. But the spec says little-endian byte order is used, which is repeated here.	[reply] [d/l] [select]
Re^3: pack/unpack woes by james289o9 (Acolyte) on Jun 14, 2022 at 22:12 UTC
I had never read the mini tutorial that you made. After looking at that and then re-reading this comment, everything at least makes sense to me. Not only that, but it actually will help me clean up some code in other modules that ive written. Thanks.	[reply]
Re^4: pack/unpack woes by AnomalousMonk (Archbishop) on Jun 15, 2022 at 06:12 UTC
Also, have you seen perlpacktut? Give a man a fish: `<%-{-{-{-<`	[reply] [d/l]
Re^2: pack/unpack woes by james289o9 (Acolyte) on Jun 14, 2022 at 21:21 UTC
Thank you AnomalousMonk, this most definitely solves my original question, and gives me some extra things to study.	[reply]