lynxis lazus has uploaded this change for review.

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gsm_utils: add gprs_tlli2tmsi()

A converter function which converts from a TLLI into a TMSI.

Change-Id: I9d3464922c89383099a5f3cdd1458c0ecc28ee18
---
M include/osmocom/gsm/gsm_utils.h
M src/gsm/gsm_utils.c
M src/gsm/libosmogsm.map
M tests/gprs/gprs_test.c
4 files changed, 34 insertions(+), 0 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/64/38764/1

diff --git a/include/osmocom/gsm/gsm_utils.h b/include/osmocom/gsm/gsm_utils.h
index b250c59..72bd131 100644
--- a/include/osmocom/gsm/gsm_utils.h
+++ b/include/osmocom/gsm/gsm_utils.h
@@ -211,6 +211,7 @@
 int gprs_tlli_type(uint32_t tlli);
 
 uint32_t gprs_tmsi2tlli(uint32_t p_tmsi, enum gprs_tlli_type type);
+uint32_t gprs_tlli2tmsi(uint32_t tlli);
 
 /* Osmocom internal, not part of any gsm spec */
 enum gsm_phys_chan_config {
diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c
index bb40339..a0df49c 100644
--- a/src/gsm/gsm_utils.c
+++ b/src/gsm/gsm_utils.c
@@ -1019,6 +1019,27 @@
 	return TLLI_RESERVED;
 }
 
+/*! Determine P-TMSI from foreign and local TLLIs
+ *
+ *  \param[in] tlli P-TMSI
+ *  \param[in] type TLLI Type we want to derive from \a p_tmsi
+ *  \returns P-TMSI or 0xffffffff on error. */
+uint32_t gprs_tlli2tmsi(uint32_t tlli)
+{
+    uint32_t ptmsi = (1 << 31) | (1 << 30);
+
+    switch (gprs_tlli_type(tlli)) {
+    case TLLI_LOCAL:
+    case TLLI_FOREIGN:
+        break;
+    default:
+        return 0xffffffff;
+    }
+
+    ptmsi |= tlli;
+    return ptmsi;
+}
+
 /*! Determine TLLI from P-TMSI
  *  \param[in] p_tmsi P-TMSI
  *  \param[in] type TLLI Type we want to derive from \a p_tmsi
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 8d17ce3..7c78347 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -73,6 +73,7 @@
 gprs_cipher_key_length;
 gprs_tlli_type;
 gprs_tmsi2tlli;
+gprs_tlli2tmsi;
 gprs_ms_net_cap_gea_supported;
 gprs_msgt_gmm_names;
 
diff --git a/tests/gprs/gprs_test.c b/tests/gprs/gprs_test.c
index 70e3009..51fe599 100644
--- a/tests/gprs/gprs_test.c
+++ b/tests/gprs/gprs_test.c
@@ -110,6 +110,16 @@
 	}
 }
 
+static void test_ptmsi_tlli()
+{
+	OSMO_ASSERT(gprs_tlli2tmsi(0xc0010203) == 0x00010203);
+	OSMO_ASSERT(gprs_tlli2tmsi(0x80010203) == 0x00010203);
+	OSMO_ASSERT(gprs_tlli2tmsi(0xf0010203) == 0xffffffff);
+
+	OSMO_ASSERT(gprs_tmsi2tlli(0x00010203, TLLI_LOCAL) == 0xc0010203);
+	OSMO_ASSERT(gprs_tmsi2tlli(0x00010203, TLLI_FOREIGN) == 0x80010203);
+}
+
 const struct log_info_cat default_categories[] = {
 };
 
@@ -124,6 +134,7 @@
 	osmo_init_logging2(ctx, &info);
 
 	test_gsm_03_03_apn();
+	test_ptmsi_tlli();
 
 	printf("Done.\n");
 	return EXIT_SUCCESS;

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