From 82be0ba4009f65007f80cfaa3c0259a7273b7df3 Mon Sep 17 00:00:00 2001
From: Ondrej Zajicek <santiago@crfreenet.org>
Date: Mon, 2 Jan 2023 15:55:55 +0100
Subject: [PATCH] Add compile-time option to enable 4-way tries instead of
 16-way ones

In some cases 16-way tries are too memory-heavy, while 4-way are
almost as efficient as the original 2-way ones.
---
 configure.ac  | 11 +++++++++++
 filter/data.h |  7 +++++++
 2 files changed, 18 insertions(+)

diff --git a/configure.ac b/configure.ac
index a326d8ad..f8ab1537 100644
--- a/configure.ac
+++ b/configure.ac
@@ -36,6 +36,12 @@ AC_ARG_ENABLE([memcheck],
   [enable_memcheck=yes]
 )
 
+AC_ARG_ENABLE([compact-tries],
+  [AS_HELP_STRING([--enable-compact-tries], [use 4-way tries instead of 16-way ones @<:@no@:>@])],
+  [],
+  [enable_compact_tries=no]
+)
+
 AC_ARG_ENABLE([pthreads],
   [AS_HELP_STRING([--enable-pthreads], [enable POSIX threads support @<:@try@:>@])],
   [],
@@ -409,6 +415,10 @@ if test "$enable_debug" = yes ; then
   fi
 fi
 
+if test "$enable_compact_tries" = yes ; then
+  AC_DEFINE([ENABLE_COMPACT_TRIES], [1], [Define to 1 if you want 4-way tries instead of 16-way ones.])
+fi
+
 CLIENT=birdcl
 CLIENT_LIBS=
 if test "$enable_client" = yes ; then
@@ -469,6 +479,7 @@ AC_MSG_RESULT([        Object directory:	$objdir])
 AC_MSG_RESULT([        Iproute2 directory:	$iproutedir])
 AC_MSG_RESULT([        System configuration:	$sysdesc])
 AC_MSG_RESULT([        Debugging:		$enable_debug])
+AC_MSG_RESULT([        Compact tries:		$enable_compact_tries])
 AC_MSG_RESULT([        POSIX threads:		$enable_pthreads])
 AC_MSG_RESULT([        Routing protocols:	$protocols])
 AC_MSG_RESULT([        LibSSH support in RPKI:	$enable_libssh])
diff --git a/filter/data.h b/filter/data.h
index 051f0932..5edeaedb 100644
--- a/filter/data.h
+++ b/filter/data.h
@@ -141,8 +141,15 @@ struct f_tree {
   void *data;
 };
 
+#ifdef ENABLE_COMPACT_TRIES
+/* Compact 4-way tries */
+#define TRIE_STEP		2
+#define TRIE_STACK_LENGTH	65
+#else
+/* Faster 16-way tries */
 #define TRIE_STEP		4
 #define TRIE_STACK_LENGTH	33
+#endif
 
 struct f_trie_node4
 {