From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=AWL,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY shortcircuit=no autolearn=no autolearn_force=no version=3.4.2 Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by dcvr.yhbt.net (Postfix) with ESMTP id 457A51F4B4 for ; Sun, 11 Oct 2020 05:55:11 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 11B88120977; Sun, 11 Oct 2020 14:54:30 +0900 (JST) Received: from xtrwkhkc.outbound-mail.sendgrid.net (xtrwkhkc.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id 2389A120959 for ; Sun, 11 Oct 2020 14:54:27 +0900 (JST) Received: by filterdrecv-p3mdw1-6685f47d68-pf696 with SMTP id filterdrecv-p3mdw1-6685f47d68-pf696-19-5F829E31-27 2020-10-11 05:54:57.893348543 +0000 UTC m=+285533.123938873 Received: from herokuapp.com (unknown) by geopod-ismtpd-5-1 (SG) with ESMTP id n0_oMK1CTqKeG4RHvtgxDQ for ; Sun, 11 Oct 2020 05:54:57.802 +0000 (UTC) Date: Sun, 11 Oct 2020 05:54:57 +0000 (UTC) From: universato@gmail.com Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 76232 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Bug X-Redmine-Issue-Id: 17257 X-Redmine-Issue-Author: universato X-Redmine-Issue-Assignee: mrkn X-Redmine-Sender: universato X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-SG-EID: =?us-ascii?Q?b0vA5U4nV4LCn7uQc1WDU+qE5iOqMsxSHQSZEBs9qDPJzuwZMB=2Fi95JjoBhk40?= =?us-ascii?Q?zc0ydrPBtjsqsoK8DG98T+8k5U1itT=2FRCjAckzR?= =?us-ascii?Q?uhSsL02=2FqHiysDiqgY84WuTMzVj+yvxv1KVrlOg?= =?us-ascii?Q?86HG1EEnii4fatswrLMLjfQiqq+X56wI+FFqT0C?= =?us-ascii?Q?67xSSv+JuGZHWqZT9hb=2F1FIKgimsJPX1qskA=2Fed?= =?us-ascii?Q?aJh7DvsHdPGGbXY40=3D?= To: ruby-core@ruby-lang.org X-Entity-ID: b/2+PoftWZ6GuOu3b0IycA== X-ML-Name: ruby-core X-Mail-Count: 100367 Subject: [ruby-core:100367] [Ruby master Bug#17257] Integer#pow(0, 1) returns 1, which is incorrect X-BeenThere: ruby-core@ruby-lang.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Ruby developers List-Id: Ruby developers List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #17257 has been updated by universato (Yoshimine Sato). `x.pow(y, m)` doesn't equal multiplying `x % m` to 1 `y` times. ```ruby p 1 * (3 % 4) * (3 % 4) #=> 9 p 3.pow(2, 4) #=> 1 ``` it is the last to mod. Method `pow` should be simply defined as `(x**y) % m`. And, `0.pow(0)` is not necessarily undefined. Many programming languages define `0 ** 0` returns 1 because it is useful. For example, Python, R, C++, C#, Java, JavaScript, PHP, Perl, MATLAB, Octave, Haskell, Julia, Crystal and Ruby e.t.c. For reference, Python has pow function like ruby's pow. Python define pow as `(x**y) % m`, and Python's pow return 0. ```python print((12 ** 0) % 1) # 0 print(pow(12, 0, 1)) # 0 ``` ---------------------------------------- Bug #17257: Integer#pow(0, 1) returns 1, which is incorrect https://bugs.ruby-lang.org/issues/17257#change-87978 * Author: universato (Yoshimine Sato) * Status: Assigned * Priority: Normal * Assignee: mrkn (Kenta Murata) * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN ---------------------------------------- Ruby 2.5.8, 2.6.6, 2.7.1 ```ruby p -1.pow(0, 1) #=> 1 p 0.pow(0, 1) #=> 1 p 1.pow(0, 1) #=> 1 p 1234567890.pow(0, 1) #=> 1 ``` These return values should be 0. Patch for test: Let's add some boundary value tests to `test_pow` of [test_numeric.rb](https://github.com/ruby/ruby/blob/e014e6bf6685f681998238ff005f6d161d43ce51/test/ruby/test_numeric.rb). ```ruby integers = [-2, -1, 0, 1, 2, 3, 6, 1234567890123456789] integers.each do |i| assert_equal(0, i.pow(0, 1), '[Bug #17257]') assert_equal(1, i.pow(0, 2)) assert_equal(1, i.pow(0, 3)) assert_equal(1, i.pow(0, 6)) assert_equal(1, i.pow(0, 1234567890123456789)) assert_equal(0, i.pow(0, -1)) assert_equal(-1, i.pow(0, -2)) assert_equal(-2, i.pow(0, -3)) assert_equal(-5, i.pow(0, -6)) assert_equal(-1234567890123456788, i.pow(0, -1234567890123456789)) end assert_equal(0, 0.pow(2, 1)) assert_equal(0, 0.pow(3, 1)) assert_equal(0, 2.pow(3, 1)) assert_equal(0, -2.pow(3, 1)) -- https://bugs.ruby-lang.org/