From 1fb680b93f3d32490581e4f3203911f1fc55601a Mon Sep 17 00:00:00 2001
From: dmiller <dmiller@e0a8ed71-7df4-0310-8962-fdc924857419>
Date: Thu, 10 Nov 2022 18:57:58 +0000
Subject: [PATCH] Use lookup table for 1-char strings, not std::map for
 string_pool.

---
 charpool.cc    | 23 +++++++++++++++++++++++
 charpool.h     |  2 ++
 string_pool.cc |  5 +++++
 3 files changed, 30 insertions(+)

diff --git a/charpool.cc b/charpool.cc
index 15b554014..d3adc331b 100644
--- a/charpool.cc
+++ b/charpool.cc
@@ -84,6 +84,24 @@ void cp_free(void) {
   return g_charpool.clear();
 }
 
+class StrTable {
+  public:
+  StrTable() {
+    memset(table, 0, sizeof(table));
+    for (int i = 1; i <= CHAR_MAX; i++) {
+      table[i*2] = static_cast<char>(i);
+    }
+  }
+  const char *get(char c) { assert(c >= 0); return &table[c*2]; }
+  private:
+  char table[2*(CHAR_MAX + 1)];
+};
+static StrTable g_table;
+
+const char *cp_char2str(char c) {
+  return g_table.get(c);
+}
+
 CharPool::CharPool(size_t init_sz) {
   assert(init_sz >= 256);
   /* Create our char pool */
@@ -103,6 +121,11 @@ void CharPool::clear(void) {
 const char *CharPool::dup(const char *src, int len) {
   if (len < 0)
     len = strlen(src);
+  if (len == 0)
+    return g_table.get('\0');
+  else if (len == 1)
+    return g_table.get(*src);
+
   int sz = len + 1;
   char *p = buckets.back() + nexti;
 
diff --git a/charpool.h b/charpool.h
index 0e7ed9e41..a60ff8328 100644
--- a/charpool.h
+++ b/charpool.h
@@ -70,6 +70,8 @@
 /* len does not include null terminator */
 const char *cp_strndup(const char *src, int len);
 const char *cp_strdup(const char *src);
+// Returns a pointer to a 1-char string
+const char *cp_char2str(char c);
 
 void cp_free(void);
 
diff --git a/string_pool.cc b/string_pool.cc
index 6ed16d635..a4e3e8bf5 100644
--- a/string_pool.cc
+++ b/string_pool.cc
@@ -100,6 +100,11 @@ typedef std::set<StringPoolItem> StringPool;
 const char *string_pool_insert_len(const char *s, int len)
 {
   static StringPool pool;
+  if (len == 0)
+    return "";
+  else if (len == 1)
+    return cp_char2str(*s);
+
   StringPoolItem spi (s, len);
 
   StringPool::iterator it = pool.insert(spi).first;