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From: alverson@decwrl.dec.com (Robert Alverson)
Newsgroups: comp.arch
Subject: Re: Wirth's "challenge"
Message-ID: <142@bacchus.DEC.COM>
Date: Thu, 12-Nov-87 21:20:57 EST
Article-I.D.: bacchus.142
Posted: Thu Nov 12 21:20:57 1987
Date-Received: Sun, 15-Nov-87 03:04:49 EST
References: <1656@geac.UUCP> <863@winchester.UUCP> <197@m2.mfci.UUCP> <902@mips.UUCP>
Reply-To: alverson@decwrl.UUCP (Robert Alverson)
Organization: Digital Equipment Corporation
Lines: 22

I found Wirth's reference to DIV and MOD extremely ironic.  In his book,
"Programming in Modula-2", he manages to define DIV the wrong way:

     `Integer division is denoted by DIV and truncates the quotient.
      For example

          15 DIV   4  =  3
         -15 DIV   4  = -3
          15 DIV (-4) = -3
  

      ... x MOD y is defined for positive x and y only.'

If it wasn't for the examples, one could argue that he meant the
floor function when he said truncate, but the examples are explicit.
If one were to implement (-15 DIV 4) using shifts, the answer would
be -4, at least using a two's complement representation.

Bob