nat: Introduce a prefix lookup tree (trie) for number rewriting
* It is a trie. The max depth of the trie is the length of the
longest prefix. The lookup is O(lookuped_prefix), but as the prefix
length is limited, the lookup time is constant.
* Each node can hold the entire prefix, has place for the rewrite
rule with up to three digits.
* A trie with 20k entries will take about 3MB ram.
* Filling the trie 100 times takes ~800ms on my i7 laptop
* 10.000.000 lookups take 315ms.. (for the same prefix).
* 93/99 lines are tested, 6/6 functions are tested, 49 of 54 branches
are tested. Only memory allocation failures are not covered
* A late addition is to handle the '+' sign and to increase the number
of chars in the rewrite prefix. The timing/line coverage has not
been updated after this change.
diff --git a/openbsc/src/osmo-bsc_nat/Makefile.am b/openbsc/src/osmo-bsc_nat/Makefile.am
index e2ba551..aae6d69 100644
--- a/openbsc/src/osmo-bsc_nat/Makefile.am
+++ b/openbsc/src/osmo-bsc_nat/Makefile.am
@@ -7,7 +7,7 @@
osmo_bsc_nat_SOURCES = bsc_filter.c bsc_mgcp_utils.c bsc_nat.c bsc_nat_utils.c \
bsc_nat_vty.c bsc_sccp.c bsc_ussd.c bsc_nat_ctrl.c \
- bsc_nat_rewrite.c bsc_nat_filter.c
+ bsc_nat_rewrite.c bsc_nat_filter.c bsc_nat_rewrite_trie.c
osmo_bsc_nat_LDADD = $(top_builddir)/src/libcommon/libcommon.a \
$(top_builddir)/src/libmgcp/libmgcp.a \
$(top_builddir)/src/libbsc/libbsc.a \