--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmfr2/pp_internal.h	Fri Apr 12 20:49:53 2024 +0000
@@ -0,0 +1,36 @@
+/*
+ * 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;
+	unsigned	cn_random_6fold;
+};
+
+/* we use the same LFSR PRNG for CN as ETSI EFR implementation */
+#define PN_INITIAL_SEED 0x70816958L   /* Pseudo noise generator seed value  */
+
+/* internal functions */
+extern void gsmfr_preproc_gen_cn(struct gsmfr_preproc_state *state,
+				 uint8_t *frame);
+extern void gsmfr_preproc_sid2cn(struct gsmfr_preproc_state *state,
+				 uint8_t *frame);
+extern void gsmfr_preproc_invalid_sid(struct gsmfr_preproc_state *state,
+				      uint8_t *frame);
+extern uint16_t gsmfr_preproc_prng(struct gsmfr_preproc_state *state,
+				   uint16_t no_bits);
+extern uint8_t gsmfr_preproc_xmaxc_mean(const uint8_t *frame);