Split the occurrance table into a seperate data structure so that it …

…can be shared between multiple StreamBMH contexts.

StreamBoyerMooreHorspool.h

@@ -185,6 +185,10 @@ typedef unsigned short sbmh_size_t;
 
 typedef void (*sbmh_data_cb)(const struct StreamBMH *ctx, const unsigned char *data, size_t len);
 
+struct StreamBMH_Occ {
+	sbmh_size_t occ[256];
+};
+
 struct StreamBMH {
 	/***** Public but read-only fields *****/
 	bool          found;
@@ -195,7 +199,6 @@ struct StreamBMH {
 
 	/***** Internal fields, do not access. *****/
 	sbmh_size_t   lookbehind_size;
-	sbmh_size_t   occ[256];
 	// Algorithm uses at most needle_len - 1 bytes of space in lookbehind buffer.
 	unsigned char lookbehind[];
 };
@@ -229,8 +232,8 @@ sbmh_reset(struct StreamBMH *restrict ctx) {
 }
 
 inline void
-sbmh_init(struct StreamBMH *restrict ctx, const unsigned char *restrict needle,
-	sbmh_size_t needle_len)
+sbmh_init(struct StreamBMH *restrict ctx, struct StreamBMH_Occ *restrict occ,
+	const unsigned char *restrict needle, sbmh_size_t needle_len)
 {
 	sbmh_size_t i;
 	unsigned int j;
@@ -242,15 +245,15 @@ sbmh_init(struct StreamBMH *restrict ctx, const unsigned char *restrict needle,
 
 	/* Initialize occurrance table. */
 	for (j = 0; j < 256; j++) {
-		ctx->occ[j] = needle_len;
+		occ->occ[j] = needle_len;
 	}
 
 	/* Populate occurance table with analysis of the needle,
 	 * ignoring last letter.
 	 */
 	if (needle_len >= 1) {
 		for (i = 0; i < needle_len - 1; i++) {
-			ctx->occ[needle[i]] = needle_len - 1 - i;
+			occ->occ[needle[i]] = needle_len - 1 - i;
 		}
 	}
 }
@@ -268,7 +271,8 @@ sbmh_lookup_char(const struct StreamBMH *restrict ctx,
 
 inline bool
 sbmh_memcmp(const struct StreamBMH *restrict ctx,
-	const unsigned char *restrict needle, const unsigned char *restrict data,
+	const unsigned char *restrict needle,
+	const unsigned char *restrict data,
 	ssize_t pos, sbmh_size_t len)
 {
 	ssize_t i = 0;
@@ -287,7 +291,7 @@ sbmh_memcmp(const struct StreamBMH *restrict ctx,
 }
 
 inline size_t
-sbmh_feed(struct StreamBMH *restrict ctx,
+sbmh_feed(struct StreamBMH *restrict ctx, const struct StreamBMH_Occ *restrict occtable,
 	const unsigned char *restrict needle, sbmh_size_t needle_len,
 	const unsigned char *restrict data, size_t len)
 {
@@ -304,7 +308,7 @@ sbmh_feed(struct StreamBMH *restrict ctx,
 	 */
 	ssize_t pos = -ctx->lookbehind_size;
 	unsigned char last_needle_char = needle[needle_len - 1];
-	const sbmh_size_t *occ = ctx->occ;
+	const sbmh_size_t *occ = occtable->occ;
 
 	if (pos < 0) {
 		SBMH_DEBUG2("[sbmh] considering lookbehind: (%s)(%s)\n",
@@ -340,7 +344,7 @@ sbmh_feed(struct StreamBMH *restrict ctx,
 					int(pos + needle_len));
 				return pos + needle_len;
 			} else {
-				pos += ctx->occ[ch];
+				pos += occ[ch];
 			}
 		}
 

StreamTest.cpp

@@ -21,15 +21,16 @@ namespace tut {
 
 		int find(const string &needle, const string &haystack) {
 			StreamBMH *ctx = (StreamBMH *) alloca(SBMH_SIZE(needle.size()));
+			StreamBMH_Occ occ;
 
 			unmatched_data.clear();
 			lookbehind.clear();
 
-			sbmh_init(ctx, (const unsigned char *) needle.c_str(), needle.size());
+			sbmh_init(ctx, &occ, (const unsigned char *) needle.c_str(), needle.size());
 			ctx->callback = append_unmatched_data;
 			ctx->user_data = this;
 
-			size_t analyzed = sbmh_feed(ctx,
+			size_t analyzed = sbmh_feed(ctx, &occ,
 				(const unsigned char *) needle.c_str(), needle.size(),
 				(const unsigned char *) haystack.c_str(), haystack.size());
 			lookbehind.assign((const char *) ctx->lookbehind, ctx->lookbehind_size);
@@ -42,17 +43,18 @@ namespace tut {
 
 		int feed_in_chunks_and_find(const string &needle, const string &haystack, int chunkSize = 1) {
 			StreamBMH *ctx = (StreamBMH *) alloca(SBMH_SIZE(needle.size()));
+			StreamBMH_Occ occ;
 
 			unmatched_data.clear();
 			lookbehind.clear();
 
-			sbmh_init(ctx, (const unsigned char *) needle.c_str(), needle.size());
+			sbmh_init(ctx, &occ, (const unsigned char *) needle.c_str(), needle.size());
 			ctx->callback = append_unmatched_data;
 			ctx->user_data = this;
 
 			size_t analyzed = 0;
 			for (string::size_type i = 0; i < haystack.size(); i += chunkSize) {
-				analyzed += sbmh_feed(ctx,
+				analyzed += sbmh_feed(ctx, &occ,
 					(const unsigned char *) needle.c_str(), needle.size(),
 					(const unsigned char *) haystack.c_str() + i,
 					std::min((int) chunkSize, (int) (haystack.size() - i)));