Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'python.': 0.04; 'think,': 0.05; 'subject:Python': 0.05; 'bits': 0.07; 'subject:code': 0.07; 'python': 0.08; 'operator,': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:80.91.229.12': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'received:lo.gmane.org': 0.09; 'python?': 0.15; 'coerced': 0.16; 'ord': 0.16; 'received:dip.t-dialin.net': 0.16; 'received:t-dialin.net': 0.16; 'subject:bit': 0.16; 'subject:writing': 0.16; 'this:': 0.16; 'wrote:': 0.18; '>>>': 0.18; 'written': 0.20; 'java': 0.21; 'trying': 0.21; 'from:addr:web.de': 0.23; 'translated': 0.23; 'byte': 0.24; "python's": 0.24; 'code': 0.25; "i'm": 0.26; 'problem': 0.29; 'seed': 0.30; '(the': 0.30; 'anyone': 0.31; "i've": 0.31; 'signed': 0.32; 'header:X-Complaints-To:1': 0.33; 'to:addr:python- list': 0.34; 'character': 0.34; 'integer': 0.34; 'think': 0.37; 'steven': 0.38; 'received:org': 0.38; 'some': 0.38; 'getting': 0.38; 'e.g.': 0.39; 'else': 0.39; 'help': 0.39; 'to:addr:python.org': 0.40; 'range': 0.61; 'results': 0.63; 'due': 0.66; 'account.': 0.80 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: Hints for writing bit-twiddling code in Python Followup-To: gmane.comp.python.general Date: Wed, 07 Dec 2011 09:21:55 +0100 Organization: None References: <4edee584$0$13933$c3e8da3$76491128@news.astraweb.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p5084b8d0.dip.t-dialin.net X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 34 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1323246133 news.xs4all.nl 6916 [2001:888:2000:d::a6]:52451 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:16774 Steven D'Aprano wrote: > I have some bit-twiddling code written in Java which I am trying to port > to Python. I'm not getting the same results though, and I think the > problem is due to differences between Java's signed byte/int/long types, > and Python's unified long integer type. E.g. Java's >>> is not exactly > the same as Python's >> operator, and a character coerced to a byte in > Java is not the same as ord(char) in Python. (The Java byte is in the > range -128...127, I think, while the ord in Python is in 0...255.) > > Can anyone point me to some good resources to help me port the Java code > to Python? > > If it helps, the Java code includes bits like this: > > long newSeed = (seed & 0xFFFFFFFFL) * 0x41A7L; > while (newSeed >= 0x80000000L) { > newSeed = (newSeed & 0x7FFFFFFFL) + (newSeed >>> 31L); > } > seed = (newSeed == 0x7FFFFFFFL) ? 0 : (int)newSeed; > > > which I've translated into: > > newseed = (seed & 0xFFFFFFFF)*0x41A7 > while (newseed >= 0x80000000): > newseed = (newseed & 0x7FFFFFFF) + (newseed >> 31) > seed = 0 if newseed == 0x7FFFFFFF else newseed & 0xFFFFFFFF I think you need to take negative ints into account. Try adding if seed & 0x80000000: # 2**31 seed -= 0x100000000 # 2**32, two's complement