From adbbeec67255f04049dbf28a3fe7573e8248f97d Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor.andersson@artifex.com>
Date: Sat, 28 Dec 2013 18:22:09 +0100
Subject: [PATCH] String interning table.

---
 Makefile    |   2 +-
 js-string.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 js.h        |   7 ++++
 3 files changed, 115 insertions(+), 1 deletion(-)
 create mode 100644 js-string.c

diff --git a/Makefile b/Makefile
index 9e836d1..ded872f 100644
--- a/Makefile
+++ b/Makefile
@@ -1,4 +1,4 @@
-SRCS := js-state.c js-load.c js-lex.c js-parse.c
+SRCS := js-state.c js-string.c js-load.c js-lex.c js-parse.c
 HDRS := js.h js-parse.h
 OBJS := $(SRCS:%.c=build/%.o)
 
diff --git a/js-string.c b/js-string.c
new file mode 100644
index 0000000..b6d61a6
--- /dev/null
+++ b/js-string.c
@@ -0,0 +1,107 @@
+#include "js.h"
+
+/* Use an AA-tree to quickly look up interned strings. */
+
+struct js_StringNode
+{
+	const char *string;
+	js_StringNode *left, *right;
+	int level;
+};
+
+static js_StringNode sentinel = { "", &sentinel, &sentinel, 0 };
+
+static js_StringNode *makestringnode(const char *string, const char **out)
+{
+	js_StringNode *node = malloc(sizeof(js_StringNode));
+	node->string = *out = strdup(string);
+	node->left = node->right = &sentinel;
+	node->level = 1;
+	return node;
+}
+
+static const char *lookup(js_StringNode *node, const char *string)
+{
+	if (node && node != &sentinel) {
+		int c = strcmp(string, node->string);
+		if (c == 0)
+			return node->string;
+		else if (c < 0)
+			return lookup(node->left, string);
+		else
+			return lookup(node->right, string);
+	}
+	return NULL;
+}
+
+static js_StringNode *skew(js_StringNode *node)
+{
+	if (node->level != 0) {
+		if (node->left->level == node->level) {
+			js_StringNode *save = node;
+			node = node->left;
+			save->left = node->right;
+			node->right = save;
+		}
+		node->right = skew(node->right);
+	}
+	return node;
+}
+
+static js_StringNode *split(js_StringNode *node)
+{
+	if (node->level != 0 && node->right->right->level == node->level) {
+		js_StringNode *save = node;
+		node = node->right;
+		save->right = node->left;
+		node->left = save;
+		node->level++;
+		node->right = split(node->right);
+	}
+	return node;
+}
+
+static js_StringNode *insert(js_StringNode *node, const char *string, const char **out)
+{
+	if (node && node != &sentinel) {
+		int c = strcmp(string, node->string);
+		if (c < 0)
+			node->left = insert(node->left, string, out);
+		else
+			node->right = insert(node->right, string, out);
+		node = skew(node);
+		node = split(node);
+		return node;
+	} else {
+		return makestringnode(string, out);
+	}
+}
+
+static void printstringnode(js_StringNode *node, int level)
+{
+	int i;
+	if (node->left != &sentinel)
+		printstringnode(node->left, level + 1);
+	for (i = 0; i < level; i++)
+		putchar(' ');
+	printf("'%s' (%d)\n", node->string, node->level);
+	if (node->right != &sentinel)
+		printstringnode(node->right, level + 1);
+}
+
+void js_printstringtree(js_State *J)
+{
+	js_StringNode *root = J->strings;
+	printf("--- string dump ---\n");
+	if (root && root != &sentinel)
+		printstringnode(root, 0);
+	printf("---\n");
+}
+
+const char *js_intern(js_State *J, const char *s)
+{
+	const char *a = lookup(J->strings, s);
+	if (!a)
+		J->strings = insert(J->strings, s, &a);
+	return a;
+}
diff --git a/js.h b/js.h
index 6e33654..b2a85b2 100644
--- a/js.h
+++ b/js.h
@@ -9,6 +9,7 @@
 #include <math.h>
 
 typedef struct js_State js_State;
+typedef struct js_StringNode js_StringNode;
 
 typedef int (*js_CFunction)(js_State *J);
 
@@ -20,12 +21,16 @@ int js_error(js_State *J, const char *fmt, ...);
 int js_loadstring(js_State *J, const char *s);
 int js_loadfile(js_State *J, const char *filename);
 
+const char *js_intern(js_State *J, const char *s);
+
 /* private */
 
 void jsP_initlex(js_State *J, const char *source);
 int jsP_lex(js_State *J);
 int jsP_parse(js_State *J);
 
+void js_printstringtree(js_State *J);
+
 struct js_State
 {
 	const char *yysource;
@@ -37,6 +42,8 @@ struct js_State
 	int lasttoken;
 	int newline;
 	int strict;
+
+	js_StringNode *strings;
 };
 
 #endif