From ec8f192fec548dd87522946319d80e4f3bc4e35c Mon Sep 17 00:00:00 2001
From: Max <msuraev@sysmocom.de>
Date: Tue, 31 May 2016 14:50:21 +0200
Subject: Add functions to detect HR/FR SID frames

Add functions which check if given FR or HR frame (packed in RTP)
contains SID (SIlence Descriptor) and corresponding tests.

Related: OS#22
Change-Id: I4051e3c0d4fb9ee93d7e9e0ef4abaf9f18e227ca
Reviewed-on: https://gerrit.osmocom.org/160
Tested-by: Jenkins Builder
Reviewed-by: Harald Welte <laforge@gnumonks.org>
---
 src/codec/gsm610.c | 39 +++++++++++++++++++++++++++++++++++++++
 src/codec/gsm620.c | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

(limited to 'src/codec')

diff --git a/src/codec/gsm610.c b/src/codec/gsm610.c
index 35f6011d..47faea21 100644
--- a/src/codec/gsm610.c
+++ b/src/codec/gsm610.c
@@ -22,6 +22,10 @@
  */
 
 #include <stdint.h>
+#include <stdbool.h>
+
+#include <osmocom/core/bitvec.h>
+#include <osmocom/core/utils.h>
 
 /* GSM FR - subjective importance bit ordering */
 	/* This array encodes GSM 05.03 Table 2.
@@ -292,3 +296,38 @@ const uint16_t gsm610_bitorder[260] = {
 	11,	/* LARc1:0 */
 	29,	/* LARc5:0 */
 };
+
+/*! \brief Check whether RTP frame contains FR SID code word according to
+ *  TS 101 318 §5.1.2
+ *  \param[in] rtp_payload Buffer with RTP payload
+ *  \param[in] payload_len Length of payload
+ *  \returns true if code word is found, false otherwise
+ */
+bool osmo_fr_check_sid(uint8_t *rtp_payload, size_t payload_len)
+{
+	struct bitvec bv;
+	uint16_t i, z_bits[] = { 59, 60, 62, 63, 65, 66, 68, 69, 71, 72, 74, 75,
+				 77, 78, 80, 81, 83, 84, 86, 87, 89, 90, 92, 93,
+				 95, 96, 115, 116, 118, 119, 121, 122, 124, 125,
+				 127, 128, 130, 131, 133, 134, 136, 137, 139,
+				 140, 142, 143, 145, 146, 148, 149, 151, 152,
+				 171, 172, 174, 175, 177, 178, 180, 181, 183,
+				 184, 186, 187, 189, 190, 192, 193, 195, 196,
+				 198, 199, 201, 202, 204, 205, 207, 208, 227,
+				 228, 230, 231, 233, 234, 236, 237, 239, 242,
+				 245, 248, 251, 254, 257, 260, 263 };
+
+	/* signature does not match Full Rate SID */
+	if ((rtp_payload[0] >> 4) != 0xD)
+		return false;
+
+	bv.data = rtp_payload;
+	bv.data_len = payload_len;
+
+	/* code word is all 0 at given bits, numbered from 1 */
+	for (i = 0; i < ARRAY_SIZE(z_bits); i++)
+		if (bitvec_get_bit_pos(&bv, z_bits[i]) != ZERO)
+			return false;
+
+	return true;
+}
diff --git a/src/codec/gsm620.c b/src/codec/gsm620.c
index f4ac9ad8..6f1a95bb 100644
--- a/src/codec/gsm620.c
+++ b/src/codec/gsm620.c
@@ -22,6 +22,10 @@
  */
 
 #include <stdint.h>
+#include <stdbool.h>
+
+#include <osmocom/core/bitvec.h>
+#include <osmocom/core/utils.h>
 
 /* GSM HR unvoiced (mode=0) frames - subjective importance bit ordering */
 	/* This array encode mapping between GSM 05.03 Table 3a (bits
@@ -260,3 +264,31 @@ const uint16_t gsm620_voiced_bitorder[112] = {
 	82,	/* Code 3:6 */
 	81,	/* Code 3:7 */
 };
+
+static inline uint16_t mask(const uint8_t msb)
+{
+	const uint16_t m = (uint16_t)1  << (msb - 1);
+	return (m - 1) ^ m;
+}
+
+/*! \brief Check whether RTP frame contains HR SID code word according to
+ *  TS 101 318 §5.2.2
+ *  \param[in] rtp_payload Buffer with RTP payload
+ *  \param[in] payload_len Length of payload
+ *  \returns true if code word is found, false otherwise
+ */
+bool osmo_hr_check_sid(uint8_t *rtp_payload, size_t payload_len)
+{
+	uint8_t i, bits[] = { 1, 2, 8, 9, 5, 4, 9, 5, 4, 9, 5, 4, 9, 5 };
+	struct bitvec bv;
+	bv.data = rtp_payload;
+	bv.data_len = payload_len;
+	bv.cur_bit = 33;
+
+	/* code word is all 1 at given bits, numbered from 1, MODE is always 3 */
+	for (i = 0; i < ARRAY_SIZE(bits); i++)
+		if (bitvec_get_uint(&bv, bits[i]) != mask(bits[i]))
+			return false;
+
+	return true;
+}
-- 
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