codec: add osmo_efr_check_sid() function

Previously existing code provides osmo_fr_check_sid() and
osmo_hr_check_sid() functions for FR1 and HR1 codecs; these functions
are used by various RTP-touching programs in the Osmocom CNI suite
when they need to differentiate between speech and SID frames.
However, there was no corresponding function of this form for EFR
codec, with the result being that the same programs that handle
speech vs SID distinction correctly for FR1 and HR1 fail to do so
for EFR.

The present change adds an osmo_efr_check_sid() function to libosmocodec
that fully mirrors previously existing osmo_fr_check_sid() and
osmo_hr_check_sid(), providing the first step toward more correct
EFR handling in programs where a SID check may be needed.

Change-Id: Iab9fb60028f4135375287bc42f5da7ca7838b5f0

1 files changed, 44 insertions, 0 deletions

diff --git a/src/codec/gsm660.c b/src/codec/gsm660.c
index 34b10dea..46ecdac3 100644
--- a/src/codec/gsm660.c
+++ b/src/codec/gsm660.c
@@ -20,6 +20,10 @@
  */
 
 #include <stdint.h>
+#include <stdbool.h>
+
+#include <osmocom/core/bitvec.h>
+#include <osmocom/core/utils.h>
 #include <osmocom/codec/codec.h>
 
 /* GSM EFR - subjective importance bit ordering */
@@ -253,3 +257,43 @@ const uint16_t gsm660_bitorder[260] = {
 	243,					/* 258 -> PULSE 4_9: b0     */
 	246,					/* 259 -> PULSE 4_10: b0    */
 };
+
+/*! Check whether RTP frame contains EFR SID code word according to
+ *  TS 101 318 §5.3.2
+ *  \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_efr_check_sid(const uint8_t *rtp_payload, size_t payload_len)
+{
+	struct bitvec bv;
+	uint16_t i;
+	static const uint8_t sid_code_word_bits[95] = {
+		/* bit numbers relative to "pure" EFR frame beginning,
+		 * not counting the signature bits. */
+		   45,  46,  48,  49,  50,  51,  52,  53,  54,  55,
+		   56,  57,  58,  59,  60,  61,  62,  63,  64,  65,
+		   66,  67,  68,  94,  95,  96,  98,  99, 100, 101,
+		  102, 103, 104, 105, 106, 107, 108, 109, 110, 111,
+		  112, 113, 114, 115, 116, 117, 118, 148, 149, 150,
+		  151, 152, 153, 154, 155, 156, 157, 158, 159, 160,
+		  161, 162, 163, 164, 165, 166, 167, 168, 169, 170,
+		  171, 196, 197, 198, 199, 200, 201, 202, 203, 204,
+		  205, 206, 207, 208, 209, 212, 213, 214, 215, 216,
+		  217, 218, 219, 220, 221 };
+
+	/* signature does not match Enhanced Full Rate SID */
+	if ((rtp_payload[0] >> 4) != 0xC)
+		return false;
+
+	bv.data = (uint8_t *) rtp_payload;
+	bv.data_len = payload_len;
+
+	/* code word is all 1 at given bits */
+	for (i = 0; i < ARRAY_SIZE(sid_code_word_bits); i++) {
+		if (bitvec_get_bit_pos(&bv, sid_code_word_bits[i]+4) != ONE)
+			return false;
+	}
+
+	return true;
+}