# by bliako on 30/08/2021
# for https://perlmonks.org/?node_id=11136212
use bigint qw/hex/;
use Digest::SHA1 qw/sha1 sha1_hex/;
my $digest_hex = sha1_hex('blah blah blah');
my $answer = hex($digest_hex);
print "$0 : starting with this number: $answer.\n";
my $min = 0;
my $max = 2**160;
my $num_guesses = 0;
my ($guess, $diff);
while( ++$num_guesses ){
$guess = $min + ($max - $min) / 2.0;
$diff = $guess - $answer;
print "entering at guess number $num_guesses, current range:\n min: $min\n max: $max\n answer: $answer\n guess: $guess\n diff: $diff\n";
if( $guess < $answer ){
print "your guess ($guess) needs to go higher ...\n";
$min = int($guess);
} elsif( $guess > $answer ){
print "your guess ($guess) needs to go lower ...\n";
$max = int($guess);
} else {
print "bingo in $num_guesses guesses! the answer was: $digest_hex and your guess was ".bigint_to_hex($guess)." ($guess).\n";
last;
}
}
sub bigint_to_hex {
# graduitously ripped off from Ben Aveling's answer in
# https://stackoverflow.com/questions/828462/how-can-i-sprintf-a-big-number-in-perl
# because sprintf("%x", bigint) does not work sadly...
my $inp = shift;
my $out = "";
while($inp){
my $chunk=$inp & 0xf;
$inp >>= 4;
$out = sprintf("%x",$chunk).$out;
}
return $out;
}