diff --git a/lib/stack.c b/lib/stack.c
index 8dfe0db..3ebe921 100644
--- a/lib/stack.c
+++ b/lib/stack.c
@@ -24,7 +24,7 @@ void free_stack(stack_t* stack)
 	xfree(stack);
 }
 
-void push(stack_t* stack, void* elt)
+void stack_push(stack_t* stack, void* elt)
 {
 	if (stack->cur_size == stack->max_size) {
 		stack->max_size *= 2;
@@ -33,8 +33,17 @@ void push(stack_t* stack, void* elt)
 	stack->arr[stack->cur_size++] = elt;
 }
 
-void* pop(stack_t* stack)
+void stack_pop(stack_t* stack)
 {
-	void* res = stack->arr[--stack->cur_size];
-	return res;
+	--stack->cur_size;
+}
+
+void* stack_peek(stack_t* stack)
+{
+	return stack->arr[stack->cur_size - 1];
+}
+
+int stack_is_empty(stack_t* stack)
+{
+	return (stack->cur_size == 0);
 }
diff --git a/lib/stack.h b/lib/stack.h
index 9417238..c3dec83 100644
--- a/lib/stack.h
+++ b/lib/stack.h
@@ -9,7 +9,10 @@ typedef struct stack stack_t;
 stack_t* alloc_stack(size_t size);
 void free_stack(stack_t* stack);
 
-void push(stack_t* stack, void* elt);
-void* pop(stack_t* stack);
+void stack_push(stack_t* stack, void* elt);
+void stack_pop(stack_t* stack);
+void* stack_peek(stack_t* stack);
+
+int stack_is_empty(stack_t* stack);
 
 #endif /* ZMAP_STACK_H */
\ No newline at end of file
diff --git a/src/expression.c b/src/expression.c
index 354b805..352c925 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -1,6 +1,8 @@
 #include "expression.h"
-#include "fieldset.H"
+#include "fieldset.h"
 
+
+#include "../lib/stack.h"
 #include "../lib/xalloc.h"
 
 /* Static helper functions */
@@ -83,6 +85,7 @@ node_t* make_field_node(char *fieldname)
 	node_t *node = alloc_node();
 	node->type = FIELD;
 	node->value.field.fieldname = fieldname;
+	node->result = 1;
 	return node;
 }
 
@@ -91,6 +94,7 @@ node_t* make_string_node(char *literal)
 	node_t *node = alloc_node();
 	node->type = STRING;
 	node->value.string_literal = literal;
+	node->result = 1;
 	return node;
 }
 
@@ -99,6 +103,7 @@ node_t* make_int_node(int literal)
 	node_t *node = alloc_node();
 	node->type = INT;
 	node->value.int_literal = literal;
+	node->result = 1;
 	return node;
 }
 
@@ -135,6 +140,88 @@ int evaluate_expression(node_t *root, fieldset_t *fields) {
 	return 0;
 }
 
+int evaluate_expression_fast(node_t *root, fieldset_t *fields) {
+	stack_t* s;
+	node_t* node;
+	if (!root) return 1;
+	s = alloc_stack(16); /* XXX Find a way to guess/know this better */
+	root->evaluated = 0;
+	stack_push(s, root);
+	int result = 1;
+	while (!stack_is_empty(s) && result) {
+		node = (node_t *) stack_peek(s);
+		if (node->type != OP) {
+			continue;
+		}
+		if (node->value.op == AND) {
+			if (!node->right_child->evaluated) {
+				stack_push(s, node->right_child);
+			} 
+			if (!node->left_child->evaluated) {
+				stack_push(s, node->left_child);
+				continue;
+			}
+
+			stack_pop(s);
+			if (!(node->left_child->result && node->right_child->result)) {
+				node->evaluated = 1;
+				result = 0;
+			}
+			node->left_child->evaluated = 0;
+			node->right_child->evaluated = 0;
+		} else if (node->value.op == OR) {
+			if (!node->right_child->evaluated) {
+				stack_push(s, node->right_child);
+			}
+			if (!node->left_child->evaluated) {
+				stack_push(s, node->left_child);
+				continue;
+			}
+
+			stack_pop(s);
+			if (!(node->left_child->result || node->right_child->result)) {
+				node->evaluated = 1;
+				result = 0;
+			}
+			node->left_child->evaluated = 0;
+			node->right_child->evaluated = 0;
+
+		} else {
+			stack_pop(s);
+			switch (node->value.op) {
+			case GT:
+				node->result = eval_gt_node(node, fields);
+				break;
+			case LT:
+				node->result = eval_lt_node(node, fields);
+				break;
+			case EQ:
+				node->result = eval_eq_node(node, fields);
+				break;
+			case NEQ:
+				node->result = !(eval_eq_node(node, fields));
+				break;
+			case LT_EQ:
+				node->result = eval_lt_eq_node(node, fields);
+				break;
+			case GT_EQ:
+				node->result = eval_gt_eq_node(node, fields);
+				break;
+			default:
+				exit(-1);
+				break;
+			}
+			node->evaluated = 1;
+			if (stack_is_empty(s)) {
+				result = node->result;
+				node->evaluated = 0;
+			}
+		}
+	}
+	free_stack(s);
+	return result;
+}
+
 void print_expression(node_t *root) {
 	if (!root) return;
 	printf("%s", "( ");
diff --git a/src/expression.h b/src/expression.h
index d65668d..e44ee2f 100644
--- a/src/expression.h
+++ b/src/expression.h
@@ -23,8 +23,8 @@ struct field_id {
 
 union node_value {
 	struct field_id field; 
-	char *string_literal;
 	uint64_t int_literal;
+	char *string_literal;
 	enum operation op;
 };
 
@@ -33,6 +33,8 @@ typedef struct node {
 	struct node *right_child;
 	enum node_type type;
 	union node_value value;
+	int evaluated;
+	int result;
 } node_t;
 
 node_t* make_op_node(enum operation op);
@@ -45,6 +47,8 @@ node_t* make_int_node(int literal);
 
 int evaluate_expression(node_t *root, fieldset_t *fields);
 
+int evaluate_expression_fast(node_t *root, fieldset_t *fields);
+
 void print_expression(node_t *root);
 
 #endif /* ZMAP_TREE_H */
\ No newline at end of file