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From: mark@applix.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: No more signals
Message-ID: <532@applix.UUCP>
Date: Mon, 22-Jun-87 14:30:55 EDT
Article-I.D.: applix.532
Posted: Mon Jun 22 14:30:55 1987
Date-Received: Tue, 23-Jun-87 07:14:44 EDT
References: <48300005@hcx1> <1207@ius2.cs.cmu.edu>
Reply-To: mark@applix.UUCP (Mark Fox)
Organization: APPLiX Inc., Westboro MA
Lines: 22
Summary: Select bit flag limited in length?

In article <1207@ius2.cs.cmu.edu> edw@ius2.cs.cmu.edu (Eddie Wyatt) writes:

   Another Unix function that I see having problems is "select".  If you
 decide to muck around with the kernal and increase the max number of 
 file descriptions to more than the number of bits in an integer then
 your going to have problems using select to do multiplexing since
 it uses an int as a bit mask for the files examined.

Vax Ultrix supports 64 file descriptors. The bit mask select receives is a
pointer to an integer (an array of integers?).  Furthermore, the first
parameter of select is the width of the bit mask, i.e., up to the value
returned by getdtablesize(2).

Now, does anyone know how the bits are laid out?  I would appreciate it if
someone would show me setbit, clearbit, and testbit algorithms that are
not machine- or width-specific.

Tnx.
-- 
                                    Mark Fox
       Applix Inc., 112 Turnpike Road, Westboro, MA 01581, (617) 870-0300
                    uucp:  seismo!harvard!m2c!applix!mark