root/lang/cplusplus/range_coder/build_table.pl

#! /usr/bin/perl

use strict;
use warnings;

use Getopt::Long;
use List::Util qw/sum max/;

my ($do_ordered);

GetOptions(
    'ordered' => \$do_ordered,
);


my @cnt = map { 0 } 0..255;

while (<>) {
    foreach my $c (split '', $_) {
        $cnt[ord $c]++;
    }
}

if ($do_ordered) {
    my @order = sort { $cnt[$b] <=> $cnt[$a] } 0..255;
    print "#define USE_ORDERED_TABLE 1\n";
    print "static unsigned char from_ordered[] = {", join(',', @order), "};\n";
    my %r = map { $order[$_] => $_ } @order;
    print "static unsigned char to_ordered[] = {", join(',', map { $r{$_} } 0..255), "};\n";
    @cnt = map { $cnt[$order[$_]] } 0..255;
}

my @freq;
my $cc = sum @cnt;
my $mult = 0x8000;
while (1) {
    print STDERR "$mult\n";
    my $acc = 0;
    for (my $i = 0; $i < 256; $i++) {
        push @freq, $acc;
        $acc += $cnt[$i] != 0 ? max(int($cnt[$i] / $cc * $mult + 0.5), 1) : 0;
    }
    last if $acc <= 0x8000;
    @freq = ();
    $mult--;
}
push @freq, 0x8000;

print "#define MAX_FREQ 0x8000\n";
print "static short freq[] __attribute__((aligned(16))) = {", join(',', map { $_ - 0x8000 } @freq), "};\n";