postgres/contrib/pg_trgm/trgm_op.c

#include "trgm.h"
#include <ctype.h>
#include "utils/array.h"
#include "catalog/pg_type.h"

float4 trgm_limit = 0.3;

PG_FUNCTION_INFO_V1(set_limit);
Datum set_limit(PG_FUNCTION_ARGS);
Datum
set_limit(PG_FUNCTION_ARGS) {
	float4 nlimit = PG_GETARG_FLOAT4(0);
	if ( nlimit < 0 || nlimit > 1.0 ) 
		elog(ERROR,"Wrong limit, should be between 0 and 1");
	trgm_limit = nlimit;
	PG_RETURN_FLOAT4(trgm_limit);
}

PG_FUNCTION_INFO_V1(show_limit);
Datum show_limit(PG_FUNCTION_ARGS);
Datum
show_limit(PG_FUNCTION_ARGS) {
	PG_RETURN_FLOAT4(trgm_limit);
}

#define WORDWAIT        0
#define INWORD          1

static int
comp_trgm(const void *a, const void *b) {
	return CMPTRGM(a,b);
}

static int
unique_array (trgm *a, int len) {
	trgm *curend, *tmp;

	curend = tmp = a;
	while (tmp - a < len)
		if ( CMPTRGM(tmp, curend) ) {
			curend++;
			CPTRGM(curend,tmp);
			tmp++;
		} else
			tmp++;
 
	return curend + 1 - a;
}


TRGM*
generate_trgm(char *str, int slen) {
	TRGM*	trg;
	char	*buf,*sptr,*bufptr;
	trgm	*tptr;
	int     state=WORDWAIT;
	int wl,len;

	trg = (TRGM*) palloc(TRGMHRDSIZE+sizeof(trgm) * (slen/2 + 1) * 3);
	trg->flag = ARRKEY;
	trg->len = TRGMHRDSIZE;

	if ( slen+LPADDING+RPADDING<3 || slen == 0 )
		return trg;

	tptr = GETARR(trg);

	buf = palloc(sizeof(char) * (slen+4));
	sptr = str;

	if ( LPADDING > 0 ) {
		*buf = ' ';
		if ( LPADDING > 1 )
			*(buf+1) = ' ';
	}

	bufptr = buf+LPADDING;
	while( sptr-str < slen ) {
		if ( state == WORDWAIT ) {
			if ( 
#ifdef	KEEPONLYALNUM
	 			isalnum((unsigned char)*sptr)
#else
				!isspace( (unsigned char)*sptr )
#endif
				) {
				*bufptr = *sptr; /* start put word in buffer */
				bufptr++;
				state = INWORD;
				if ( sptr-str == slen-1 /* last char */ )
					goto gettrg;
			}
		} else {
			if (
#ifdef	KEEPONLYALNUM
	 			!isalnum((unsigned char)*sptr)
#else
				isspace( (unsigned char)*sptr )			
#endif
				) {
gettrg:
				/* word in buffer, so count trigrams */
				*bufptr = ' ';
				*(bufptr+1) = ' ';
				wl = bufptr - (buf+LPADDING) - 2 + LPADDING + RPADDING;
				if ( wl<=0 ) {
					bufptr = buf+LPADDING;
					state = WORDWAIT;
					sptr++;
					continue;
				}

#ifdef IGNORECASE
				do { /* lower word */
					int wwl = bufptr-buf;
					bufptr = buf+LPADDING;
					while( bufptr-buf < wwl ) {
						*bufptr = tolower( (unsigned char) *bufptr );
						bufptr++;
					}
				} while(0);
#endif
				bufptr = buf;
				/* set trigrams */
				while( bufptr-buf < wl ) {
					CPTRGM(tptr, bufptr);
					bufptr++;
					tptr++;
				}
				bufptr = buf+LPADDING;
				state = WORDWAIT;
			} else {
				*bufptr = *sptr; /* put in buffer */
				bufptr++;
				if ( sptr-str == slen-1 )
					goto gettrg;
			}
		}
		sptr++;
	}

	pfree(buf);

	if ( (len=tptr-GETARR(trg)) == 0 ) 
		return trg;

	if ( len>0 ) {
		qsort( (void*)GETARR(trg), len, sizeof(trgm), comp_trgm );
		len = unique_array( GETARR(trg), len );
	} 

	trg->len = CALCGTSIZE(ARRKEY, len);

	return trg;
}


PG_FUNCTION_INFO_V1(show_trgm);
Datum show_trgm(PG_FUNCTION_ARGS);
Datum
show_trgm(PG_FUNCTION_ARGS) {
	text       *in = PG_GETARG_TEXT_P(0);
	TRGM	*trg;
	Datum *d;
	ArrayType *a;
	trgm *ptr;

	trg = generate_trgm(VARDATA(in), VARSIZE(in) - VARHDRSZ);
	d = (Datum*)palloc( sizeof(Datum)*(1+ARRNELEM(trg)) );

	ptr = GETARR(trg);
	while( ptr-GETARR(trg) < ARRNELEM(trg) ) {
		text *item=(text*)palloc(VARHDRSZ + 3);
		VARATT_SIZEP(item) = VARHDRSZ+3;
		CPTRGM(VARDATA(item), ptr);
		d[ ptr-GETARR(trg) ] = PointerGetDatum(item);
		ptr++;
	}

	a = construct_array(
		d,
		ARRNELEM(trg),
		TEXTOID,
		-1,
		false,
		'i'
	);

	ptr = GETARR(trg);
	while( ptr-GETARR(trg) < ARRNELEM(trg) ) {
		pfree(DatumGetPointer(d[ ptr-GETARR(trg) ]));
		ptr++;
	}
	
	pfree(d);
	pfree(trg);
	PG_FREE_IF_COPY(in,0);

	PG_RETURN_POINTER(a);
}

float4
cnt_sml(TRGM *trg1, TRGM *trg2) {
	trgm	*ptr1, *ptr2;
	int count=0;
	int len1, len2;
	
	ptr1 = GETARR(trg1);
	ptr2 = GETARR(trg2);
	
	len1 = ARRNELEM(trg1);
	len2 = ARRNELEM(trg2);

	while( ptr1 - GETARR(trg1) < len1 && ptr2 - GETARR(trg2) < len2 ) {
		int res = CMPTRGM(ptr1,ptr2);
		if ( res < 0 ) {
			ptr1++;
		} else if ( res > 0 ) {
			ptr2++;
		} else {
			ptr1++;
			ptr2++;
			count++;
		}
	}

#ifdef DIVUNION
	return ( ( ((float4)count) / ((float4)(len1+len2-count)) ) );
#else
	return ( ((float)count) / ((float)( (len1>len2) ? len1 : len2 )) );
#endif

}

PG_FUNCTION_INFO_V1(similarity);
Datum similarity(PG_FUNCTION_ARGS);
Datum
similarity(PG_FUNCTION_ARGS) {
	text       *in1 = PG_GETARG_TEXT_P(0);
	text       *in2 = PG_GETARG_TEXT_P(1);
	TRGM    *trg1, *trg2;
	float4 res;

	trg1 = generate_trgm(VARDATA(in1), VARSIZE(in1) - VARHDRSZ);
	trg2 = generate_trgm(VARDATA(in2), VARSIZE(in2) - VARHDRSZ);

	res = cnt_sml(trg1,trg2);
	
	pfree(trg1);
	pfree(trg2);
	PG_FREE_IF_COPY(in1,0);
	PG_FREE_IF_COPY(in2,1);
	
	PG_RETURN_FLOAT4(res);
}

PG_FUNCTION_INFO_V1(similarity_op);
Datum similarity_op(PG_FUNCTION_ARGS);
Datum
similarity_op(PG_FUNCTION_ARGS) {
	float4 res=DatumGetFloat4( DirectFunctionCall2(
		similarity,
		PG_GETARG_DATUM(0),
		PG_GETARG_DATUM(1)
	) );
	PG_RETURN_BOOL( res >= trgm_limit );
}