libgsmhr1 TFO: require BFI=0 and SID=0 for homing In order for a received frame to be recognized as DHF, we need not only the correct bit pattern, but also BFI=0 and SID=0. The BFI=0 requirement should be obvious, while the SID=0 requirement is needed only for HR codec. With FR and EFR, SID classification comes from the payload bits and no separate check is needed - but in HR we get an out-of-band SID ternary flag. When SID=1, no payload bits are used at all; when SID=2, we use only the first 33 bits of the payload. Therefore, it is proper to conditionalize DHF acceptance on SID=0. We already implemented this logic in the just finished full decoder; now bring TFO code into agreement.

/*
 * This header file is internal to libgsmfr2;
 * here we define our state structure for the Rx DTX preprocessor component.
 */

enum rx_dtx_st {
	NO_DATA = 0,
	SPEECH,
	SPEECH_MUTING,
	COMFORT_NOISE,
	LOST_SID,
	CN_MUTING,
};

struct gsmfr_preproc_state {
	enum rx_dtx_st	rx_state;
	uint8_t		speech_frame[GSMFR_RTP_FRAME_LEN];
	uint8_t		sid_prefix[5];
	uint8_t		sid_xmaxc;
	uint32_t	cn_random_lfsr;
	uint8_t		cn_random_6fold;
	uint8_t		dtxd_nodata_count;
	uint8_t		dtxd_sid_flag;
};

/* we use the same LFSR PRNG for CN as ETSI EFR implementation */
#define PN_INITIAL_SEED 0x70816958L   /* Pseudo noise generator seed value  */