Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!caen!umich!sharkey!fmsrl7!art-sy!news
From: chap@art-sy.detroit.mi.us (j chapman flack)
Newsgroups: comp.unix.programmer
Subject: Re: comp_t
Keywords: Accounting, comp_t, funny floats...
Message-ID: <9105060921.aa11316@art-sy.detroit.mi.us>
Date: 6 May 91 13:21:37 GMT
References: <512@eskimo.celestial.com>
Sender: chap@art-sy.detroit.mi.us (j chapman flack)
Reply-To: chap@art-sy.detroit.mi.us (j chapman flack)
Organization: Appropriate Roles for Technology
Lines: 27

In article <512@eskimo.celestial.com> nanook@eskimo.celestial.com (Robert Dinse) writes:
>"comp_t", which is packed into an unsigned short (16 bits). The
>comments say:
>
>	/* 13-bit fraction, 3-bit exponent */

I just messed with that recently myself.  By running a bunch of commands that
took known amounts of time (sleep(1) is handy for that) and trying to make
sense of the resulting comp_ts, I came up with the following theory:

mantissa = comp_t & 0x1FFF
exponent = comp_t & 0xE000

double ticks = ldexp( (double)mantissa, 3*exponent)

The extra factor of 3 in the exponent bothers me, but it was consistent with
the various values I tried.  You'll probably want to run a number of trials
yourself.  I would be delighted, actually, to learn that I'm wrong and have
someone provide a more sensible explanation.

Wouldn't it be nice if AT&T's comment included the information that needs
to be included?
-- 
Chap Flack                         Their tanks will rust.  Our songs will last.
chap@art-sy.detroit.mi.us                                   -Mikos Theodorakis

Nothing I say represents Appropriate Roles for Technology unless I say it does.