added string set library

"struct strset" is a hashed string set: you can add strings to this
library, and it stores them as a set of unique strings.  You can get
the size of the set, and you can enumerate through all values.

This will be used to replace the linear tagTracker library.

src/Makefile.am

@@ -92,6 +92,7 @@ mpd_headers = \
 	tag_save.h \
 	tagTracker.h \
 	utf8.h \
+	strset.h \
 	utils.h \
 	volume.h \
 	ioops.h \
@@ -158,6 +159,7 @@ mpd_SOURCES = \
 	tag_print.c \
 	tag_save.c \
 	tagTracker.c \
+	strset.c \
 	utils.c \
 	volume.c \
 	utf8.c \

src/strset.c

@@ -0,0 +1,144 @@
+/* the Music Player Daemon (MPD)
+ * Copyright (C) 2008 Max Kellermann <max@duempel.org>
+ * This project's homepage is: http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include "strset.h"
+#include "utils.h"
+#include "os_compat.h"
+
+#define NUM_SLOTS 16384
+
+struct strset_slot {
+	struct strset_slot *next;
+	const char *value;
+};
+
+struct strset {
+	unsigned size;
+
+	struct strset_slot *current_slot;
+	unsigned next_slot;
+
+	struct strset_slot slots[NUM_SLOTS];
+};
+
+static unsigned calc_hash(const char *p) {
+	unsigned hash = 5381;
+
+	assert(p != NULL);
+
+	while (*p != 0)
+		hash = (hash << 5) + hash + *p++;
+
+	return hash;
+}
+
+mpd_malloc struct strset *strset_new(void)
+{
+	struct strset *set = xcalloc(1, sizeof(*set));
+	return set;
+}
+
+void strset_free(struct strset *set)
+{
+	unsigned i;
+
+	for (i = 0; i < NUM_SLOTS; ++i) {
+		struct strset_slot *slot = set->slots[i].next, *next;
+
+		while (slot != NULL) {
+			next = slot->next;
+			free(slot);
+			slot = next;
+		}
+	}
+
+	free(set);
+}
+
+void strset_add(struct strset *set, const char *value)
+{
+	struct strset_slot *base_slot
+		= &set->slots[calc_hash(value) % NUM_SLOTS];
+	struct strset_slot *slot = base_slot;
+
+	if (base_slot->value == NULL) {
+		/* empty slot - put into base_slot */
+		assert(base_slot->next == NULL);
+
+		base_slot->value = value;
+		++set->size;
+		return;
+	}
+
+	for (slot = base_slot->next; slot != NULL; slot = slot->next)
+		if (strcmp(slot->value, value) == 0)
+			/* found it - do nothing */
+			return;
+
+	/* insert it into the slot chain */
+	slot = xmalloc(sizeof(*slot));
+	slot->next = base_slot->next;
+	slot->value = value;
+	base_slot->next = slot;
+	++set->size;
+}
+
+int strset_get(const struct strset *set, const char *value)
+{
+	const struct strset_slot *slot = &set->slots[calc_hash(value)];
+
+	if (slot->value == NULL)
+		return 0;
+
+	for (slot = slot->next; slot != NULL; slot = slot->next)
+		if (strcmp(slot->value, value) == 0)
+			/* found it - do nothing */
+			return 1;
+
+	return 0;
+}
+
+unsigned strset_size(const struct strset *set)
+{
+	return set->size;
+}
+
+void strset_rewind(struct strset *set)
+{
+	set->current_slot = NULL;
+	set->next_slot = 0;
+}
+
+const char *strset_next(struct strset *set)
+{
+	if (set->current_slot != NULL && set->current_slot->next != NULL) {
+		set->current_slot = set->current_slot->next;
+		return set->current_slot->value;
+	}
+
+	while (set->next_slot < NUM_SLOTS &&
+	       set->slots[set->next_slot].value == NULL)
+		++set->next_slot;
+
+	if (set->next_slot >= NUM_SLOTS)
+		return NULL;
+
+	set->current_slot = &set->slots[set->next_slot++];
+	return set->current_slot->value;
+}
+

src/strset.h

@@ -0,0 +1,49 @@
+/* the Music Player Daemon (MPD)
+ * Copyright (C) 2008 Max Kellermann <max@duempel.org>
+ * This project's homepage is: http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+/**
+ * "struct strset" is a hashed string set: you can add strings to this
+ * library, and it stores them as a set of unique strings.  You can
+ * get the size of the set, and you can enumerate through all values.
+ *
+ * It is important to note that the strset does not copy the string
+ * values - it stores the exact pointers it was given in strset_add().
+ */
+
+#ifndef STRSET_H
+#define STRSET_H
+
+#include "gcc.h"
+
+struct strset;
+
+mpd_malloc struct strset *strset_new(void);
+
+void strset_free(struct strset *set);
+
+void strset_add(struct strset *set, const char *value);
+
+int strset_get(const struct strset *set, const char *value);
+
+unsigned strset_size(const struct strset *set);
+
+void strset_rewind(struct strset *set);
+
+const char *strset_next(struct strset *set);
+
+#endif