Fwd: [Montandalar/advtrains] lag ? (Issue #12) v1 PROPOSED

Y. Wang: 1
 unify (un)escape lookups; minor optimizations

 1 files changed, 44 insertions(+), 21 deletions(-)

[PATCH] unify (un)escape lookups; minor optimizations Export this patch

Blockhead,

I came up with this set of changes that seems to slightly improve
performance, at least with the set of data I used for the test (a 3.6MB
advtrains_interlocking.ls file from a set of savefiles sent to me by a
server admin). Part of this is taken from a patch that I filed to
advtrains-devel a while ago.

For Festus' test, however, I do not think this will bring much
improvement (if at all).
---
 serialize_lib/serialize.lua | 65 +++++++++++++++++++++++++------------
 1 file changed, 44 insertions(+), 21 deletions(-)

diff --git a/serialize_lib/serialize.lua b/serialize_lib/serialize.lua
index 78ddcfd..be7e29f 100644
--- a/serialize_lib/serialize.lua
+++ b/serialize_lib/serialize.lua
@@ -40,13 +40,30 @@ In strings the following characters are escaped by &
 All other characters are unchanged as they bear no special meaning.
 ]]
 
+local escape_table = {
+	["&"] = "&",
+	[":"] = ":",
+	["\r"] = "r",
+	["\n"] = "n",
+}
+local unescape_table = {}
+local escape_match, unescape_match = {}, {}
+for k, v in pairs(escape_table) do
+	unescape_table["&"..v] = k
+	escape_table[k] = "&"..v
+	table.insert(escape_match, k)
+	table.insert(unescape_match, v)
+end
+escape_match = "[" .. table.concat(escape_match) .. "]"
+unescape_match = "&[" .. table.concat(unescape_match) .. "]"
+
+escape_lookup = {}
+unescape_lookup = {}
+
 local write_table, literal_to_string, escape_chars, table_is_empty
 
 function table_is_empty(t)
-	for _,_ in pairs(t) do
-		return false
-	end
-	return true
+	return next(t) == nil
 end
 
 function write_table(t, file, config)
@@ -77,32 +94,35 @@ function write_table(t, file, config)
 end
 
 function value_to_string(t)
-	if type(t)=="table" then
+	local tp = type(t)
+	if tp=="table" then
 		file:close()
 		error("Can not serialize a table in the key position!")
-	elseif type(t)=="boolean" then
+	elseif tp=="boolean" then
 		if t then
 			return "B1"
 		else
 			return "B0"
 		end
-	elseif type(t)=="number" then
+	elseif tp=="number" then
 		return "N"..t
-	elseif type(t)=="string" then
+	elseif tp=="string" then
 		return "S"..escape_chars(t)
 	else
 		--error("Can not serialize '"..type(t).."' type!")
-		return "S<function>"
+		return string.format("S<%s>", tp)
 	end
 	return str
 end
 
 function escape_chars(str)
-	local rstr = string.gsub(str, "&", "&&")
-	rstr = string.gsub(rstr, ":", "&:")
-	rstr = string.gsub(rstr, "\r", "&r")
-	rstr = string.gsub(rstr, "\n", "&n")
-	return rstr
+	local s = escape_lookup[str]
+	if s then
+		return s
+	end
+	s = string.gsub(str, escape_match, escape_table)
+	escape_lookup[str] = s
+	return s
 end
 
 ------
@@ -145,7 +165,8 @@ function string_to_value(str, table_allow)
 	local rest = string.sub(str, 2)
 	if first=="T" then
 		if table_allow then
-			return {}, true
+			-- pre-allocate some hash entries to reduce rehashing for small tables
+			return {x = nil, y = nil, z = nil}, true
 		else
 			file:close()
 			error("Table not allowed in key component!")
@@ -175,12 +196,14 @@ function string_to_value(str, table_allow)
 	end
 end
 
-function unescape_chars(str) --TODO
-	local rstr = string.gsub(str, "&:", ":")
-	rstr = string.gsub(rstr, "&n", "\n")
-	rstr = string.gsub(rstr, "&r", "\r")
-	rstr = string.gsub(rstr, "&&", "&")
-	return rstr
+function unescape_chars(str)
+	local s = unescape_lookup[str]
+	if s then
+		return s
+	end
+	s = string.gsub(str, unescape_match, unescape_table)
+	unescape_lookup[str] = s
+	return s
 end
 
 ------
-- 
2.35.1