From 931cb6e71b72035013c9433e39264a9b33e2b89b Mon Sep 17 00:00:00 2001
From: Egor <egor@patchysicp.xyz>
Date: Sun, 15 Jun 2025 12:39:38 +0300
Subject: [PATCH] irc: use a perfect hash function for command matching

---
 Makefile.am |  4 ++++
 src/irc.cpp | 23 +++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/Makefile.am b/Makefile.am
index d3d9ccc..3d7481d 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -60,3 +60,7 @@ pch.mk: common.hpp.$(PCHEXT)
 	@: >pch.mk
 -include pch.mk
 endif
+
+.PHONY: gperf
+gperf:
+	sed -n 's/.*MATCH_COMMAND("\([^"]*\)").*/\1/p' $(srcdir)/src/irc.cpp | gperf -m1 -k1-3
diff --git a/src/irc.cpp b/src/irc.cpp
index dea4e3b..b726126 100644
--- a/src/irc.cpp
+++ b/src/irc.cpp
@@ -236,10 +236,33 @@ static void cont_pass(Client *client, int res) {
 		newUser(client);
 	}
 }
+#define USE_COMMAND_HASH
+#ifdef USE_COMMAND_HASH
+constexpr size_t command_hash(std::string_view sv) {
+	if (sv.size() < 3)
+		return -1;
+	constexpr unsigned char table[32] = {
+		43, 1, 27, 12, 5, 3,
+		43, 7, 22, 10, 27, 12, 11, 13, 7, 1,
+		0, 16, 15, 0, 0, 0, 11, 3, 43, 43,
+		43, 43, 43, 43, 43, 43,
+	};
+	return table[sv[0]&31] + table[sv[1]&31] + table[sv[2]&31] + sv.size();
+}
+#endif
+
+#ifdef USE_COMMAND_HASH
+#define MATCH_BEGIN switch (command_hash(command)) {
+#define MATCH_COMMAND(s) break; case command_hash(s##sv): if (command == s##sv)
+#define MATCH_ELSE break; default:
+#define MATCH_END break; }
+#else
 #define MATCH_BEGIN if (0)
 #define MATCH_COMMAND(s) else if (command == s##sv)
 #define MATCH_ELSE else
 #define MATCH_END
+#endif
+
 int irc_process_line(Client *client, char *source, std::string_view command, int argc, char *args[]) {
 	(void)source;
 	databuf.clear();
-- 
2.56.0