File: metaphone_c.c

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libtext-metaphone-perl 20160805-1
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/* STUFF TO DO
 * - Make max_phonemes useful
 */
 
#include "metaphone.h"
#include "metachar.h"

#include <stdlib.h>
#include <string.h>
#include <ctype.h>

/* I suppose I could have been using a character pointer instead of
 * accesssing the array directly... */

/* Look at the next letter in the word */
#define Next_Letter (toupper(word[w_idx+1]))
/* Look at the current letter in the word */
#define Curr_Letter (toupper(word[w_idx]))
/* Go N letters back. */
#define Look_Back_Letter(n) (w_idx >= n ? toupper(word[w_idx-n]) : '\0') 
/* Previous letter.  I dunno, should this return null on failure? */
#define Prev_Letter (Look_Back_Letter(1))
/* Look two letters down.  It makes sure you don't walk off the string. */
#define After_Next_Letter   (Next_Letter != '\0' ? toupper(word[w_idx+2]) \
                                                 : '\0')
#define Look_Ahead_Letter(n) (toupper(Lookahead(word+w_idx, n)))

                         
/* Allows us to safely look ahead an arbitrary # of letters */
/* I probably could have just used strlen... */
char Lookahead(char * word, int how_far) {
    char letter_ahead = '\0';  /* null by default */
    int idx;
    for(idx = 0;  word[idx] != '\0' && idx < how_far;  idx++);
        /* Edge forward in the string... */
        
    letter_ahead = word[idx];  /* idx will be either == to how_far or
                                * at the end of the string
                                */
    return letter_ahead;
}


/* phonize one letter */
#define Phonize(c)  {phoned_word[p_idx++] = c;}
/* How long is the phoned word? */
#define Phone_Len   (p_idx)

/* Note is a letter is a 'break' in the word */
#define Isbreak(c)  (!isalpha(c))


char *metaphone ( char *word, size_t max_phonemes ) {
    int w_idx   = 0;    /* point in the phonization we're at. */
    int p_idx   = 0;    /* end of the phoned phrase */
    char *phoned_word;
    
    /* Assume largest possible if we're given no limit */
    if( max_phonemes == 0 )
        max_phonemes = strlen(word);

    /* It's +2 because X -> KS can result in the phoned word being
       one larger than the original word.
    */
    phoned_word = calloc( max_phonemes + 2, sizeof(char) );

    /*-- The first phoneme has to be processed specially. --*/
    /* Find our first letter */
    for( ;  !isalpha(Curr_Letter);  w_idx++ ) {
        /* On the off chance we were given nothing but crap... */
        if( Curr_Letter == '\0' ) {
            return phoned_word;
        }
    }   
    
    switch (Curr_Letter) {
        /* AE becomes E */
        case 'A':
            if( Next_Letter == 'E' ) {
                Phonize('E');
                w_idx+=2;
            }
            /* Remember, preserve vowels at the beginning */
            else {
                Phonize('A');
                w_idx++;
            }
            break;
        /* [GKP]N becomes N */
        case 'G':
        case 'K':
        case 'P':
            if( Next_Letter == 'N' ) {
                Phonize('N');
                w_idx+=2;
            }
            break;
        /* WH becomes H, 
           WR becomes R 
           W if followed by a vowel */
        case 'W':
            if( Next_Letter == 'H' ||
                Next_Letter == 'R' ) 
            {
              Phonize(Next_Letter);
              w_idx+=2;
            }
            else if ( isvowel(Next_Letter) ) {
              Phonize('W');
              w_idx+=2;
            }
            /* else ignore */
            break;
        /* X becomes S */
        case 'X':
            Phonize('S');
            w_idx++;
            break;
        /* Vowels are kept */
        /* We did A already
        case 'A':
        case 'a':
        */
        case 'E':
        case 'I':
        case 'O':
        case 'U':
            Phonize(Curr_Letter);
            w_idx++;
            break;
        default:
            /* do nothing */
            break;
    }
    
    
    
    /* On to the metaphoning */
    for(;
        Curr_Letter != '\0'     && 
        (max_phonemes == 0 || Phone_Len < max_phonemes);  
        w_idx++
    ) {
        /* How many letters to skip because an eariler encoding handled     
         * multiple letters */
        unsigned short int skip_letter = 0; 
                                

        /* THOUGHT:  It would be nice if, rather than having things like...
         * well, SCI.  For SCI you encode the S, then have to remember
         * to skip the C.  So the phonome SCI invades both S and C.  It would
         * be better, IMHO, to skip the C from the S part of the encoding.
         * Hell, I'm trying it.
         */
    
        /* Ignore non-alphas */
        if( !isalpha(Curr_Letter) )
            continue;
            
        /* Drop duplicates, except CC */
        if( Curr_Letter == Prev_Letter &&
            Curr_Letter != 'C' )
            continue;
        
        switch (Curr_Letter) {
            /* B -> B unless in MB */
            case 'B':
                if( Prev_Letter != 'M' )
                    Phonize('B');
                break;
            /* 'sh' if -CIA- or -CH, but not SCH, except SCHW.
             * (SCHW is handled in S)
             *  S if -CI-, -CE- or -CY-
             *  dropped if -SCI-, SCE-, -SCY- (handed in S)
             *  else K
             */
            case 'C':
                if( MAKESOFT(Next_Letter) ) {   /* C[IEY] */
                    if( After_Next_Letter == 'A' &&
                        Next_Letter == 'I' ) { /* CIA */
                        Phonize(SH);
                    }
                    /* SC[IEY] */
                    else if ( Prev_Letter == 'S' ) {
                      /* Dropped */
                    }
                    else {
                      Phonize('S');
                    }
                }
                else if ( Next_Letter == 'H' ) {
#ifndef USE_TRADITIONAL_METAPHONE
                    if( After_Next_Letter == 'R' ||
                        Prev_Letter == 'S' ) { /* Christ, School */
                        Phonize('K');
                    }
                    else {
                        Phonize(SH);
                    }
#else
                    Phonize(SH);
#endif
                    skip_letter++;
                }
                else {
                    Phonize('K');
                }
                break;
            /* J if in -DGE-, -DGI- or -DGY-
             * else T
             */
            case 'D':
                if( Next_Letter == 'G' &&
                    MAKESOFT(After_Next_Letter) ) {
                    Phonize('J');
                    skip_letter++;
                }
                else
                    Phonize('T');
                break;
            /* F if in -GH and not B--GH, D--GH, -H--GH, -H---GH
             * else dropped if -GNED, -GN, 
             * else dropped if -DGE-, -DGI- or -DGY- (handled in D)
             * else J if in -GE-, -GI, -GY and not GG
             * else K
             */
            case 'G':
                if( Next_Letter == 'H' ) {
                    if( !( NOGHTOF(Look_Back_Letter(3)) ||
                           Look_Back_Letter(4) == 'H' ) ) {
                        Phonize('F');
                        skip_letter++;
                    }
                    else {
                        /* silent */
                    }
                }
                else if( Next_Letter == 'N' ) {
                    if( Isbreak(After_Next_Letter) ||
                        ( After_Next_Letter == 'E' &&
                          Look_Ahead_Letter(3) == 'D' ) ) {
                        /* dropped */
                    }
                    else
                        Phonize('K');
                }
                else if( MAKESOFT(Next_Letter) &&
                         Prev_Letter != 'G' ) {
                    Phonize('J');
                }
                else {
                    Phonize('K');
                }
                break;
            /* H if before a vowel and not after C,G,P,S,T */
            case 'H':
                if( isvowel(Next_Letter) &&
                    !AFFECTH(Prev_Letter) )
                    Phonize('H');
                break;
            /* dropped if after C
             * else K
             */
            case 'K':
                if( Prev_Letter != 'C' )
                    Phonize('K');
                break;
            /* F if before H
             * else P
             */
            case 'P':
                if( Next_Letter == 'H' ) {
                    Phonize('F');
                }
                else {
                    Phonize('P');
                }
                break;
            /* K
             */
            case 'Q':
                Phonize('K');
                break;
            /* 'sh' in -SH-, -SIO- or -SIA- or -SCHW-
             * else S
             */
            case 'S':
                if( Next_Letter == 'I' &&
                    ( After_Next_Letter == 'O' ||
                      After_Next_Letter == 'A' ) ) {
                    Phonize(SH);
                }
                else if ( Next_Letter == 'H' ) {
                    Phonize(SH);
                    skip_letter++;
                }
#ifndef USE_TRADITIONAL_METAPHONE
                else if ( Next_Letter == 'C' &&
                      Look_Ahead_Letter(2) == 'H' &&
                      Look_Ahead_Letter(3) == 'W' ) {
                    Phonize(SH);
                    skip_letter += 2;
                }
#endif
                else {
                    Phonize('S');
                }
                break;
            /* 'sh' in -TIA- or -TIO-
             * else 'th' before H
             * else T
             */
            case 'T':
                if( Next_Letter == 'I' &&
                    ( After_Next_Letter == 'O' ||
                      After_Next_Letter == 'A' ) ) {
                    Phonize(SH);
                }
                else if ( Next_Letter == 'H' ) {
                    Phonize(TH);
                    skip_letter++;
                }
                else {
                    Phonize('T');
                }
                break;
            /* F */
            case 'V':
                Phonize('F');
                break;
            /* W before a vowel, else dropped */
            case 'W':
                if( isvowel(Next_Letter) )
                    Phonize('W');
                break;
            /* KS */
            case 'X':
                Phonize('K');
                Phonize('S');
                break;
            /* Y if followed by a vowel */
            case 'Y':
                if( isvowel(Next_Letter) )
                    Phonize('Y');
                break;
            /* S */
            case 'Z':
                Phonize('S');
                break;
            /* No transformation */
            case 'F':
            case 'J':
            case 'L':
            case 'M':
            case 'N':
            case 'R':
                Phonize(Curr_Letter);
                break;
            default:
                /* nothing */
                break;
        }
        
        w_idx += skip_letter;
    }
    
    return phoned_word;
}