From 2725202771f079f0f04c5a55cc572410f72f0645 Mon Sep 17 00:00:00 2001
From: Dennis Luxen <info@project-osrm.org>
Date: Fri, 31 May 2024 19:58:57 +0200
Subject: [PATCH] Use Lemire's fast check whether to escape a JSON string
 (#6923)

---
 include/util/string_util.hpp | 39 ++++++++++++++++++++----------------
 1 file changed, 22 insertions(+), 17 deletions(-)

diff --git a/include/util/string_util.hpp b/include/util/string_util.hpp
index 874a1d284..4e6351137 100644
--- a/include/util/string_util.hpp
+++ b/include/util/string_util.hpp
@@ -1,8 +1,9 @@
 #ifndef STRING_UTIL_HPP
 #define STRING_UTIL_HPP
 
+#include <array>
 #include <cctype>
-
+#include <cstddef>
 #include <random>
 #include <string>
 #include <vector>
@@ -10,26 +11,30 @@
 namespace osrm::util
 {
 
+// implements Lemire's table-based escape needs check
+// cf. https://lemire.me/blog/2024/05/31/quickly-checking-whether-a-string-needs-escaping/
+inline static constexpr std::array<uint8_t, 256> json_quotable_character = []() constexpr
+{
+    std::array<uint8_t, 256> result{};
+    for (auto i = 0; i < 32; i++)
+    {
+        result[i] = 1;
+    }
+    for (auto i : {'"', '\\'})
+    {
+        result[i] = 1;
+    }
+    return result;
+}();
+
 inline bool RequiresJSONStringEscaping(const std::string &string)
 {
-    for (const char letter : string)
+    uint8_t needs = 0;
+    for (uint8_t c : string)
     {
-        switch (letter)
-        {
-        case '\\':
-        case '"':
-        case '/':
-        case '\b':
-        case '\f':
-        case '\n':
-        case '\r':
-        case '\t':
-            return true;
-        default:
-            continue;
-        }
+        needs |= json_quotable_character[c];
     }
-    return false;
+    return needs;
 }
 
 inline void EscapeJSONString(const std::string &input, std::string &output)