Class PorterStemmer

The main part of the stemming algorithm starts here. b is a buffer holding a word to be stemmed. The letters are in b[k0], b[k0+1] ... ending at b[k]. In fact k0 = 0 in this demo program. k is readjusted downwards as the stemming progresses. Zero termination is not in fact used in the algorithm.

Note that only lower case sequences are stemmed. Forcing to lower case should be done before stem(...) is called.

m() measures the number of consonant sequences between k0 and j.
if c is a consonant sequence and v a vowel sequence, and <..>
indicates arbitrary presence,

   <c><v>       gives 0
   <c>vc<v>     gives 1
   <c>vcvc<v>   gives 2
   <c>vcvcvc<v> gives 3
   ....

cvc(i) is TRUE <=> i-2,i-1,i has the form consonant - vowel - consonant
and also if the second c is not w,x or y. this is used when trying to
restore an e at the end of a short  e.g.

   cav(e), lov(e), hop(e), crim(e), but
   snow, box, tray.

step1ab() gets rid of plurals and -ed or -ing. e.g.

caresses -> caress ponies -> poni ties -> ti caress -> caress cats -> cat

feed -> feed agreed -> agree disabled -> disable

matting -> mat mating -> mate meeting -> meet milling -> mill messing -> mess

meetings -> meet

step2() maps double suffices to single ones. so -ization ( = -ize plus -ation) maps to -ize etc. note that the string before the suffix must give m() > 0.

step3() dels with -ic-, -full, -ness etc. similar strategy to step2.

In stem(p,i,j), p is a char pointer, and the string to be stemmed is from p[i] to p[j] inclusive. Typically i is zero and j is the offset to the last character of a string, (p[j+1] == ''). The stemmer adjusts the characters p[i] ... p[j] and returns the new end-point of the string, k. Stemming never increases word length, so i <= k <= j. To turn the stemmer into a module, declare 'stem' as extern, and delete the remainder of this file.