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Path: utzoo!watmath!clyde!burl!ulysses!bellcore!decvax!linus!philabs!pwa-b!mmintl!franka
From: franka@mmintl.UUCP (Frank Adams)
Newsgroups: net.lang
Subject: Re: Integer division: a winner declared
Message-ID: <1164@mmintl.UUCP>
Date: Tue, 4-Mar-86 16:28:12 EST
Article-I.D.: mmintl.1164
Posted: Tue Mar  4 16:28:12 1986
Date-Received: Sat, 8-Mar-86 21:01:52 EST
References: <11610@ucbvax.BERKELEY.EDU> <5100003@ccvaxa> <548@ism780c.UUCP> <1970@peora.UUCP> <127@diablo.ARPA>
Reply-To: franka@mmintl.UUCP (Frank Adams)
Organization: Multimate International, E. Hartford, CT
Lines: 37
Keywords: semi-:-) re the winner, Knuth, Ada, C
Summary: Not by me it isn't


In article <127@diablo.ARPA> avg@diablo.UUCP (Allen VanGelder) writes:
>Ada clearly has it right.  Knuth agrees, but spells "rem" differently.
>Ada examples:
>	   5/ 3   =  1		 5 rem  3 =  2		 5 mod  3 =  2
>	(-5)/ 3   = -1		-5 rem  3 = -2		-5 mod  3 =  1
>	   5/(-3) = -1		 5 rem -3 =  2		 5 mod -3 = -2
>	(-5)/(-3) =  1		-5 rem -3 = -2		-5 mod -3 = -1
>
>(a mod b) is the answer to the question,
>	"What element in the field Z_b is congruent to a?"
>
>I can't imagine implementing -5/3 = -2.  If you really need this, I
>would assume you also need the Ada "mod" on the same numbers.  So do
>	m = a mod b;
>	q = (a - m) / b;
>with very little overhead.

A step in the right direction, but it still doesn't divide and round.
ALGOL does it this way, but it hasn't been heard from since.

(By the way, one advantage of -5/3 = -2 is that it makes it easier to do
a divide and round if one is not available already.  One can write:

   (a + b / 2) / b

instead of

   if (a > 0) then
      (a + b / 2) / b
   else
      (a - b / 2) / b

or similar results from mucking around with some variant of the signum
function.)

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Multimate International    52 Oakland Ave North    E. Hartford, CT 06108