🚀 go-pugleaf

In article <4879@ganymede.inmos.co.uk> mph@lion.inmos.co.uk (Mike
Harrison) writes:

| >To take a concrete example, let's ignore the existence of <ctype.h> and
| >suppose that we want to test whether or not a given character is a lowercase
| >letter.  I claim that, to me, the condition "(c >= 'a' && c <= 'z')" is a
| >simpler expression than "(c < 'a' || c > 'z')".  I immediately recognize the
| >idiom in the former, but the latter causes a perceptible delay as I mentally
| >translate the condition.  (If you disagree with this example, invent another
| >one--unless you want to claim that there is *no* condition that is simpler
| >than its inverse.)

Three things:

    1)	On EBCDIC systems, either of the above tests would evaluate
	true for some things that are not lower case alphabetic, since
	there are some characters (10?) between 'i' & 'j';

    2)	Obviously the above test will not work for character sets that
	have more than 26 alphabetic characters;

    3)	If you are worried about micro optimization, and your compiler
	doesn't recognize the optimization, you generally get faster
	code if you rewrite the test as:

		if (((unsigned) c - 'a') <= ((unsigned) 'z' - 'a'))

	This is because only one branch is done.
--
Michael Meissner	email: meissner@osf.org		phone: 617-621-8861
Open Software Foundation, 11 Cambridge Center, Cambridge, MA

Catproof is an oxymoron, Childproof is nearly so