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First, check pack:

> V An unsigned long (32-bit) in "VAX" (little-endian) order.

Have you noticed the pattern?

bytes chars 36353935 ----> 36 35 39 35 ----> 6 5 9 5 | | | | first 4 digits reverse | | | | 595661 -------------> 5956 ------> 6 5 9 5

It works for any input greater or equal to 1000:

#! /usr/bin/perl use warnings; use strict; use Test::More; sub what { my ($input) = @_; my $unpacked = unpack "V", $input; my $result = join "", map chr hex, sprintf("%x\n", $unpacked) =~ / +(..)/g; is $result, reverse substr $input, 0, 4; } what($_) for 1000 .. 2000, 2e4, 3e5, 4e6, 5e7, 6e8, 7e9, 8e10, 9e11, 2 ** 64 - 3; done_testing();

Update: For numbers fitting into integer, you can also use

reverse($input) % 10_000

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord }map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

In reply to Re: Understanding Unpack on Decimal Value by choroba
in thread Understanding Unpack on Decimal Value by arblargan

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