Path: csiph.com!aioe.org!.POSTED!not-for-mail
From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
Newsgroups: comp.lang.java.programmer
Subject: Re: Will Math.random return 0.0?
Date: Sat, 16 Jul 2016 14:15:33 -0400
Organization: Aioe.org NNTP Server
Lines: 32
Message-ID: <nmdtk7$19to$1@gioia.aioe.org>
References: <rand-20160716162126@ram.dialup.fu-berlin.de> <nmdoj7$o5v$1@news2.informatik.uni-stuttgart.de>
NNTP-Posting-Host: 7SK6yTFfqwlIPNBLl3l7Qg.user.gioia.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0
X-Notice: Filtered by postfilter v. 0.8.2
Xref: csiph.com comp.lang.java.programmer:34917

On 7/16/2016 12:49 PM, Thomas Richter wrote:
> Am 16.07.2016 um 17:24 schrieb Stefan Ram:
>>   I wrote the following program.
>>
>> public final class Main
>> { public static void main( final java.lang.String[] args )
>>   { while( java.lang.Math.random() != 0.0 );
>>     java.lang.System.out.println( "0.0" ); }}
>>
>>   What do you expect it's (average) runtime to be
>>   on average hardware?
>>
>>   Can we be sure that it will ever terminate?
>
> No, you cannot.

Sure?

>             If random() is implemented by the average (=bad) linear
> congruence generator, then zero will never be the output of random().

Not true.

First LCG's can have seed zero and a good cycle as long as the add part 
is non-zero.

Second even for an MLCG (with add part zero) where seed can not be
zero, then the random numbers can include zero simply by subtracting
one.

Arne