Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!pilchuck!dataio!gtenmc!csp
From: csp@gtenmc.UUCP (Charudutta S. Palkar)
Newsgroups: comp.lang.c
Subject: Cryptic code == Optimized code ? YES : NO ;
Keywords: compliers , optimization , development
Message-ID: <861@gtenmc.UUCP>
Date: 10 Sep 90 21:36:32 GMT
Reply-To: csp@gtenmc.UUCP (Chardutta S. Palkar)
Organization: GTE Telecom, Inc.  Bothell, WA
Lines: 84


   C is a very good language ie to say it good to good programmers and
   bad to bad programmers. 

   I would like to discuss a few issues that I have noticed during programming
   in C.

   Note : sections of examples are logically equivalent

   Example 1: Variable k is of type int.

	a )        if ( a > b )
		     k = 7;
		   else
		     k = 5;

	 b )       k = a > b ? 7 : 5;

	 c )       k = ( a > b ) * 2 + 5;

   Example 2: Variables a and b are of the same type either int , char , float.

	 a )      a = a + b;
		  b = a - b;
		  a = a - b;

	 b )      a = a - ( b = ( a = a + b ) - b );

	 c )      a -= b = ( a += b ) - b;

   Example 3: Variables a and b are of the same type either int , char

	 a )     a = a ^ b;
		 b = a ^ b;
		 a = a ^ b;

	 b )     a = a ^ ( b = b ^ ( a = a ^ b ));

	 c )     a ^= b ^= a ^= b;

   Example 4: Variables a and b are pointers to structures with 
	      self referential pointers as fields.

	      typedef struct fool
	      {
		  struct fool *nxt , *prv;
		  char data;
	       }  node , *ptr;

               ptr a, b;

	    a )       b->prv = a;
		      b->nxt = a->nxt;
		      b->nxt->prv = b;
		      a->nxt = b;

	    b )       ( b->nxt = ( b->prv = a )->nxt )->prv = a->nxt = b;


   The functions of examples 2 & 3 is to interchange values 2 variables
of numeric type. Example 4 is insertion of a node in a circularly
doublely linked list.

   My questions are :

      1 ) Will the code generated by a non-optimizing comiler be more
	  more optimised as a set of statements get combined into one
	  expression.

      2 ) Will the same happen even with an optimizing compiler.

      3 ) Should such kind of compaction be favoured for development.

   Thanx In advance.

   C S Palkar - csp@gtenmc.gtetele.com
		csp@gtenmc.UUCP

   PS : Any mistakes in the above code spotted , be pointed out and
	other such examples I would like to know of.

   " I only speak for myself "

   K&R C > ANSI C.