contrib/triage/bisect-num

#!/usr/bin/perl
#
# Copyright 2025 The ChromiumOS Authors
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
#
# Maintainer: Ross Zwisler <zwisler@google.com>
#
# bisect-num: Help automate a first-build bisect for a given issue.
# See http://go/cros-imt-first-build-codelab
# Given an <old_revision> and <new_revision>, this script will give you a
# middle revision to test at each step until we find two adjacent builds, one
# which is good and one which is bad.  This script also allows us to update the
# build we are actually testing, in the case that some images are unavailable
# because of build issues.
#
# Usage: bisect-num <old_revision> <new_revision>
#   $ bisect-num 15474 15506
#   range (15474 (good) - 15506 (bad), in 5 steps) Next revision to test: 15490
#   Good? (y/n) or enter revision actually tested:
use strict;
use warnings;

if ($#ARGV != 1) {
    print "Usage: $0 <old_revision> <new_revision>\n";
    exit 0;
}

my $min = shift(@ARGV);
my $max = shift(@ARGV);

# Function for log2 calculator
sub log2
{
    my $n = shift;
    # using pre-defined log function
    return log($n) / log(2);
}

while (1) {
    my $mid = int(($min + $max) / 2);

    $mid++ if ($mid == $min);

    if ($mid == $max) {
        print "First bad number: $mid\n";
        exit 0;
    }

    while (1) {
        my $steps = int(log2($max - $min));
        print "range ($min (good) - $max (bad), in $steps steps) Next revision to test: $mid\n";
        print "Good? (y/n) or enter revision actually tested: ";

        my $answer = <STDIN>;
        exit if (!$answer);
        chomp($answer);

        if ($answer eq 'y') {
            print "YES\n";
            $min = $mid;
            last;
        } elsif ($answer eq "n") {
            print "NO\n";
            $max = $mid;
            last;
        } elsif ($answer =~ /^(\d)+$/) {
            $mid = $answer;
        }
    }
}