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This directory contains some examples illustrating techniques for extracting 
high-performance from flex scanners.  Each program implements a simplified 
version of the Unix "wc" tool: read text from stdin and print the number of 
characters, words, and lines present in the text.  All programs were compiled 
using gcc (version unavailable, sorry) with the -O flag, and run on a 
SPARCstation 1+.  The input used was a PostScript file, mainly containing 
figures, with the following "wc" counts: 
 
	lines  words  characters 
	214217 635954 2592172 
 
 
The basic principles illustrated by these programs are: 
 
	- match as much text with each rule as possible 
	- adding rules does not slow you down! 
	- avoid backing up 
 
and the big caveat that comes with them is: 
 
	- you buy performance with decreased maintainability; make 
	  sure you really need it before applying the above techniques. 
 
See the "Performance Considerations" section of flexdoc for more 
details regarding these principles. 
 
 
The different versions of "wc": 
 
	mywc.c 
		a simple but fairly efficient C version 
 
	wc1.l	a naive flex "wc" implementation 
 
	wc2.l	somewhat faster; adds rules to match multiple tokens at once 
 
	wc3.l	faster still; adds more rules to match longer runs of tokens 
 
	wc4.l	fastest; still more rules added; hard to do much better 
		using flex (or, I suspect, hand-coding) 
 
	wc5.l	identical to wc3.l except one rule has been slightly 
		shortened, introducing backing-up 
 
Timing results (all times in user CPU seconds): 
 
	program	  time 	 notes 
	-------   ----   ----- 
	wc1       16.4   default flex table compression (= -Cem) 
	wc1        6.7   -Cf compression option 
	/bin/wc	   5.8	 Sun's standard "wc" tool 
	mywc	   4.6   simple but better C implementation! 
	wc2	   4.6   as good as C implementation; built using -Cf 
	wc3	   3.8   -Cf 
	wc4	   3.3   -Cf 
	wc5	   5.7   -Cf; ouch, backing up is expensive