Add another hamming function. The former are for varbit parameters. The

later are for text parameters (like the other functions). Also, add another
operator ~@~.

hamming.c

@@ -129,3 +129,99 @@ Datum hamming_op(PG_FUNCTION_ARGS)
 
 	PG_RETURN_BOOL(res >= pgs_hamming_threshold);
 }
+
+PG_FUNCTION_INFO_V1(hamming_text);
+
+Datum
+hamming_text(PG_FUNCTION_ARGS)
+{
+	char		*a, *b;
+	int			alen, blen;
+	char		*pa, *pb;
+	int			maxlen;
+	float4		res = 0.0;
+
+	a = DatumGetPointer(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(0))));
+	b = DatumGetPointer(DirectFunctionCall1(textout, PointerGetDatum(PG_GETARG_TEXT_P(1))));
+
+	alen = strlen(a);
+	blen = strlen(b);
+
+	if (alen > PGS_MAX_STR_LEN || blen > PGS_MAX_STR_LEN)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("argument exceeds the maximum length of %d bytes",
+					PGS_MAX_STR_LEN)));
+
+	elog(DEBUG1, "alen: %d; blen: %d", alen, blen);
+
+	if (alen != blen)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				errmsg("bit strings must have the same length")));
+
+	elog(DEBUG1, "a: %s ; b: %s", a, b);
+
+	/* alen and blen have the same length */
+	maxlen = alen;
+
+	pa = a;
+	pb = b;
+	while (*pa != '\0')
+	{
+		elog(DEBUG4, "a: %c ; b: %c", *pa, *pb);
+
+		/* are these bit strings? */
+		if ((*pa != '0' && *pa != '1') || (*pb != '0' && *pb != '1'))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+					errmsg("arguments must contain only 0 or 1")));
+		if (*pa++ != *pb++)
+			res++;
+	}
+
+	elog(DEBUG1, "is normalized: %d", pgs_hamming_is_normalized);
+	elog(DEBUG1, "maximum length: %d", maxlen);
+
+	elog(DEBUG1, "hammingdistance(%s, %s) = %.3f", DatumGetCString(a), DatumGetCString(b), res);
+
+	/* if one string has zero length then return one */
+	if (maxlen == 0)
+	{
+		PG_RETURN_FLOAT4(1.0);
+	}
+	else if (pgs_hamming_is_normalized)
+	{
+		res = 1.0 - (res / maxlen);
+		elog(DEBUG1, "hamming(%s, %s) = %.3f", DatumGetCString(a), DatumGetCString(b), res);
+		PG_RETURN_FLOAT4(res);
+	}
+	else
+	{
+		PG_RETURN_FLOAT4(res);
+	}
+}
+
+PG_FUNCTION_INFO_V1(hamming_text_op);
+
+Datum hamming_text_op(PG_FUNCTION_ARGS)
+{
+	float4	res;
+
+	/*
+	 * store *_is_normalized value temporarily 'cause
+	 * threshold (we're comparing against) is normalized
+	 */
+	bool	tmp = pgs_hamming_is_normalized;
+	pgs_hamming_is_normalized = true;
+
+	res = DatumGetFloat4(DirectFunctionCall2(
+					hamming_text,
+					PG_GETARG_DATUM(0),
+					PG_GETARG_DATUM(1)));
+
+	/* we're done; back to the previous value */
+	pgs_hamming_is_normalized = tmp;
+
+	PG_RETURN_BOOL(res >= pgs_hamming_threshold);
+}

pg_similarity.sql.in

@@ -80,13 +80,21 @@ CREATE OR REPLACE FUNCTION hamming_op (varbit, varbit) RETURNS bool
 AS 'MODULE_PATHNAME', 'hamming_op'
 LANGUAGE C STABLE STRICT;
 
---CREATE OPERATOR ~@@ (
---	LEFTARG = text,
---	RIGHTARG = text,
---	PROCEDURE = hamming_op,
---	COMMUTATOR = '~@@',
---	JOIN = contjoinsel
---);
+CREATE OR REPLACE FUNCTION hamming_text (text, text) RETURNS float4
+AS 'MODULE_PATHNAME','hamming_text'
+LANGUAGE C IMMUTABLE STRICT;
+
+CREATE OR REPLACE FUNCTION hamming_text_op (text, text) RETURNS bool
+AS 'MODULE_PATHNAME', 'hamming_text_op'
+LANGUAGE C STABLE STRICT;
+
+CREATE OPERATOR ~@~ (
+	LEFTARG = text,
+	RIGHTARG = text,
+	PROCEDURE = hamming_text_op,
+	COMMUTATOR = '~@~',
+	JOIN = contjoinsel
+);
 
 -- Jaccard
 CREATE OR REPLACE FUNCTION jaccard (text, text) RETURNS float4

similarity.h

@@ -214,6 +214,8 @@ extern Datum PGS_EXPORT euclidean(PG_FUNCTION_ARGS);
 extern Datum PGS_EXPORT euclidean_op(PG_FUNCTION_ARGS);
 extern Datum PGS_EXPORT hamming(PG_FUNCTION_ARGS);
 extern Datum PGS_EXPORT hamming_op(PG_FUNCTION_ARGS);
+extern Datum PGS_EXPORT hamming_text(PG_FUNCTION_ARGS);
+extern Datum PGS_EXPORT hamming_text_op(PG_FUNCTION_ARGS);
 extern Datum PGS_EXPORT jaccard(PG_FUNCTION_ARGS);
 extern Datum PGS_EXPORT jaccard_op(PG_FUNCTION_ARGS);
 extern Datum PGS_EXPORT jaro(PG_FUNCTION_ARGS);

uninstall_pg_similarity.sql

@@ -19,7 +19,9 @@ DROP OPERATOR ~!! (text, text);
 DROP FUNCTION euclidean (text, text);
 DROP FUNCTION euclidean_op (text, text);
 
---DROP OPERATOR ~@@ (text, text);
+DROP OPERATOR ~@~ (text, text);
+DROP FUNCTION hamming_text (text, text);
+DROP FUNCTION hamming_text_op (text, text);
 DROP FUNCTION hamming (varbit, varbit);
 DROP FUNCTION hamming_op (varbit, varbit);