From 0e48ac1dfe9896bc62bcfb02218adc4d97e8a6c6 Mon Sep 17 00:00:00 2001
From: Jonathan Coates <git@squiddev.cc>
Date: Thu, 4 May 2023 19:46:40 +0100
Subject: [PATCH] Speed up JSON string parsing

We now use Lua patterns to find runs of characters. This makes string
parsing 3-4x faster. Ish - I've not run any exact benchmarks.

Closes #1408
---
 .../data/computercraft/lua/rom/apis/textutils.lua  | 14 +++++++++++---
 projects/fabric/src/main/resources/fabric.mod.json |  2 +-
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/projects/core/src/main/resources/data/computercraft/lua/rom/apis/textutils.lua b/projects/core/src/main/resources/data/computercraft/lua/rom/apis/textutils.lua
index 87b731186..353dbb799 100644
--- a/projects/core/src/main/resources/data/computercraft/lua/rom/apis/textutils.lua
+++ b/projects/core/src/main/resources/data/computercraft/lua/rom/apis/textutils.lua
@@ -533,12 +533,18 @@ do
     local function parse_string(str, pos, terminate)
         local buf, n = {}, 1
 
+        -- We attempt to match all non-special characters at once using Lua patterns, as this
+        -- provides a significant speed boost. This is all characters >= " " except \ and the
+        -- terminator (' or ").
+        local char_pat = "^[ !#-[%]^-\255]+"
+        if terminate == "'" then char_pat = "^[ -&(-[%]^-\255]+" end
+
         while true do
             local c = sub(str, pos, pos)
             if c == "" then error_at(pos, "Unexpected end of input, expected '\"'.") end
             if c == terminate then break end
 
-            if c == '\\' then
+            if c == "\\" then
                 -- Handle the various escapes
                 c = sub(str, pos + 1, pos + 1)
                 if c == "" then error_at(pos, "Unexpected end of input, expected escape sequence.") end
@@ -552,8 +558,10 @@ do
                     if not unesc then error_at(pos + 1, "Unknown escape character %q.", c) end
                     buf[n], n, pos = unesc, n + 1, pos + 2
                 end
-            elseif c >= '\x20' then
-                buf[n], n, pos = c, n + 1, pos + 1
+            elseif c >= " " then
+                local _, finish = find(str, char_pat, pos)
+                buf[n], n = sub(str, pos, finish), n + 1
+                pos = finish + 1
             else
                 error_at(pos + 1, "Unescaped whitespace %q.", c)
             end
diff --git a/projects/fabric/src/main/resources/fabric.mod.json b/projects/fabric/src/main/resources/fabric.mod.json
index 0e638d0c4..189e29bcd 100644
--- a/projects/fabric/src/main/resources/fabric.mod.json
+++ b/projects/fabric/src/main/resources/fabric.mod.json
@@ -47,7 +47,7 @@
     ],
     "depends": {
         "fabricloader": ">=0.14.17",
-        "fabric-api": ">=0.78.0",
+        "fabric-api": ">=0.80.0",
         "minecraft": ">=1.19.4 <1.20"
     },
     "accessWidener": "computercraft.accesswidener"