From 060caf653daee1fca1d0007fc641ea7750c2279b Mon Sep 17 00:00:00 2001
From: itchyny <itchyny@hatena.ne.jp>
Date: Mon, 30 Aug 2021 20:23:04 +0900
Subject: [PATCH] truncate values offset and stack limits to reduce allocations
 (fix #86)

---
 execute.go | 15 +++++++++++----
 stack.go   |  4 ++--
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/execute.go b/execute.go
index 6bba7401..2e1e0869 100644
--- a/execute.go
+++ b/execute.go
@@ -205,8 +205,7 @@ loop:
 				if callpc >= 0 {
 					saveindex = index
 				} else {
-					s := env.scopes.pop().(scope)
-					callpc, saveindex = s.pc, s.saveindex
+					callpc, saveindex = env.popscope()
 				}
 			} else {
 				env.scopes.save(&saveindex, &limit)
@@ -228,8 +227,7 @@ loop:
 			if backtrack {
 				break loop
 			}
-			s := env.scopes.pop().(scope)
-			pc, env.scopes.index = s.pc, s.saveindex
+			pc, env.scopes.index = env.popscope()
 			if env.scopes.empty() {
 				return env.pop(), true
 			}
@@ -349,6 +347,15 @@ func (env *env) pop() interface{} {
 	return env.stack.pop()
 }
 
+func (env *env) popscope() (int, int) {
+	free := env.scopes.index > env.scopes.limit
+	s := env.scopes.pop().(scope)
+	if free {
+		env.offset = s.offset
+	}
+	return s.pc, s.saveindex
+}
+
 func (env *env) pushfork(pc int) {
 	f := fork{pc: pc, expdepth: env.expdepth}
 	env.stack.save(&f.stackindex, &f.stacklimit)
diff --git a/stack.go b/stack.go
index 11816aac..f629d28e 100644
--- a/stack.go
+++ b/stack.go
@@ -44,10 +44,10 @@ func (s *stack) empty() bool {
 }
 
 func (s *stack) save(index, limit *int) {
-	if s.index >= s.limit {
+	*index, *limit = s.index, s.limit
+	if s.index > s.limit {
 		s.limit = s.index
 	}
-	*index, *limit = s.index, s.limit
 }
 
 func (s *stack) restore(index, limit int) {