Array indexing vs. pointers...

[Michael Chastain]

Good grief.  Say NO to low-level performance tweaking.

I prefer to use the most natural data representation I can think of.
If something's an array, I don't dink around inside it with pointers.

More precisely, I restrict my pointer operations to:

	-- assignment/parameter passing/return value
	-- dereferencing
	-- address-of: p2 = &p1[5];

As another poster mentioned:

	/* Array */
	for ( iArg = 1; iArg < argc; iArg++ )
		ProcessArg( argv[iArg] );

	/* Pointer */
	while ( --argc )
		ProcessArg( *++argv );

I find the first version more writeable.  More debuggable.  More
readable.  And more likely to be correct *the first time*.

If you had to debug this code with a typical sdb-like debugger, which
would you rather look at?   "iArg" or "argv"?  I find wild array
references easier to deal with than wild pointer references:  less
likely to occur, easier to debug/find when they do.  I find all of
these properties more useful than the small and doubtful performance
gain that I can get by *increasing the entropy* of my code and data.

Suppose you told your boss: "my next project will be:
	-- 20% sooner
	-- 20% cleaner
	-- 30% less bugs
	--  5% larger
	--  5% slower (in non-real-time-critical areas)"
What do you think he or she would say?

#if	FLAME
The last word for you efficiency geeks:

#if	BIG_COMPUTER
My array code vectorizes more easily than your pointers-that-might-be-
aliased code.  So while you're saving a cycle here, a cycle there, I'm
getting 400% performance improvements just by recompiling.
#endif

#if	INTEL_8086
While your object code is thrashing via ES:BX, my object code is loading
ES:BX with a fixed value and loading array indexes into SI and DI.  And
if you point a normal 32-bit pointer into global data or a stack, while
I'm using an array index into a (sufficiently well-known) structure, my
code is likely to get 16-bit address computations off of DS or SS:BP.
Your code will thrash through ES:BX.
#endif

#endif	FLAME

Michael Chastain
mec at ardent.com
{hplabs,uunet}!ardent!mec
"He who dies with the most FRIENDS wins."