shared: strbuf - add string de-duplication facility

2 files changed, 211 insertions, 0 deletions

diff --git a/src/shared/strbuf.c b/src/shared/strbuf.c
new file mode 100644
index 0000000000..5c858cb68e
--- /dev/null
+++ b/src/shared/strbuf.c
@@ -0,0 +1,155 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 Kay Sievers <kay.sievers@vrfy.org>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdlib.h>
+#include <string.h>
+
+#include "util.h"
+#include "strbuf.h"
+
+struct strbuf *strbuf_new(void) {
+        struct strbuf *str;
+
+        str = new0(struct strbuf, 1);
+        if (!str)
+                return NULL;
+
+        str->buf = new0(char, 1);
+        if (!str->buf)
+                goto err;
+        str->len = 1;
+
+        str->root = new0(struct strbuf_node, 1);
+        if (!str->root)
+                goto err;
+        str->nodes_count = 1;
+        return str;
+err:
+        free(str->buf);
+        free(str->root);
+        free(str);
+        return NULL;
+}
+
+static void strbuf_node_cleanup(struct strbuf_node *node) {
+        size_t i;
+
+        for (i = 0; i < node->children_count; i++)
+                strbuf_node_cleanup(node->children[i].child);
+        free(node->children);
+        free(node);
+}
+
+void strbuf_complete(struct strbuf *str) {
+        if (!str)
+                return;
+        if (str->root)
+                strbuf_node_cleanup(str->root);
+        str->root = NULL;
+}
+
+void strbuf_cleanup(struct strbuf *str) {
+        if (!str)
+                return;
+        if (str->root)
+                strbuf_node_cleanup(str->root);
+        free(str->buf);
+        free(str);
+}
+
+static int strbuf_children_cmp(const void *v1, const void *v2) {
+        const struct strbuf_child_entry *n1 = v1;
+        const struct strbuf_child_entry *n2 = v2;
+
+        return n1->c - n2->c;
+}
+
+ssize_t strbuf_add_string(struct strbuf *str, const char *s, size_t len) {
+        uint8_t c;
+        struct strbuf_node *node;
+        size_t depth;
+        char *buf_new;
+        struct strbuf_child_entry *child;
+        struct strbuf_node *node_child;
+        ssize_t off;
+
+        if (!str->root)
+                return -EINVAL;
+
+        /* search string; start from last character to find possibly matching tails */
+        if (len == 0)
+                return 0;
+        str->in_count++;
+        str->in_len += len;
+
+        node = str->root;
+        c = s[len-1];
+        for (depth = 0; depth <= len; depth++) {
+                struct strbuf_child_entry search;
+
+                /* match against current node */
+                off = node->value_off + node->value_len - len;
+                if (depth == len || (node->value_len >= len && memcmp(str->buf + off, s, len) == 0)) {
+                        str->dedup_len += len;
+                        str->dedup_count++;
+                        return off;
+                }
+
+                /* lookup child node */
+                c = s[len - 1 - depth];
+                search.c = c;
+                child = bsearch(&search, node->children, node->children_count, sizeof(struct strbuf_child_entry),
+                                strbuf_children_cmp);
+                if (!child)
+                        break;
+                node = child->child;
+        }
+
+        /* add new string */
+        buf_new = realloc(str->buf, str->len + len+1);
+        if (!buf_new)
+                return -ENOMEM;
+        str->buf = buf_new;
+        off = str->len;
+        memcpy(str->buf + off, s, len);
+        str->len += len;
+        str->buf[str->len++] = '\0';
+
+        /* new node */
+        node_child = new0(struct strbuf_node, 1);
+        if (!node_child)
+                return -ENOMEM;
+        str->nodes_count++;
+        node_child->value_off = off;
+        node_child->value_len = len;
+
+        /* extend array, add new entry, sort for bisection */
+        child = realloc(node->children, (node->children_count + 1) * sizeof(struct strbuf_child_entry));
+        if (!child)
+                return -ENOMEM;
+        node->children = child;
+        node->children[node->children_count].c = c;
+        node->children[node->children_count].child = node_child;
+        node->children_count++;
+        qsort(node->children, node->children_count, sizeof(struct strbuf_child_entry), strbuf_children_cmp);
+
+        return off;
+}
diff --git a/src/shared/strbuf.h b/src/shared/strbuf.h
new file mode 100644
index 0000000000..35f232ddb0
--- /dev/null
+++ b/src/shared/strbuf.h
@@ -0,0 +1,56 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+#pragma once
+
+/***
+  This file is part of systemd.
+
+  Copyright 2012 Kay Sievers <kay.sievers@vrfy.org>
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <stdarg.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+struct strbuf {
+        char *buf;
+        size_t len;
+        struct strbuf_node *root;
+
+        size_t nodes_count;
+        size_t in_count;
+        size_t in_len;
+        size_t dedup_len;
+        size_t dedup_count;
+};
+
+struct strbuf_node {
+        size_t value_off;
+        size_t value_len;
+
+        struct strbuf_child_entry *children;
+        uint8_t children_count;
+};
+
+struct strbuf_child_entry {
+        uint8_t c;
+        struct strbuf_node *child;
+};
+
+struct strbuf *strbuf_new(void);
+ssize_t strbuf_add_string(struct strbuf *str, const char *s, size_t len);
+void strbuf_complete(struct strbuf *str);
+void strbuf_cleanup(struct strbuf *str);