1 byte:                       0..127
2 bytes:                    128..etc
3 bytes:                 16_384
4 bytes:              2_097_152
5 bytes:            268_435_456
6 bytes:         34_359_738_368
7 bytes:      4_398_046_511_104
8 bytes:    562_949_953_421_312
9 bytes: 72_057_594_037_927_936

##</code><code>##

sub compress_uint {
   my ($uint) = @_;
   my $compressed = '';
   while ($uint >= 128) {
      $compressed .= chr(($uint & 127) | 128);
      $uint >>= 7;
   }
   $compressed .= chr($uint);
}

for (100, 1000, 100000) {
   print $fh compress_uint($_);
}

##</code><code>##

sub decompress_uint {
   our $compressed; local *compressed = \($_[0]);
   my $bytes_read = 0;
   my $uint = 0;
   for (;;) {
      die if length($compressed) == $bytes_read;
      my $byte = ord(substr($compressed, $bytes_read++, 1));
      $uint = ($uint << 7) | ($byte & 127);
      last if $byte & 128;
   }
   $compressed = substr($compressed, $bytes_read);
}

my $raw = do { local $/; <$fh> };
my @nums;
while (length($raw)) {
   push @nums, decompress_uint($raw);
}