--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/dhf_subst2.c	Sun May 12 21:36:26 2024 +0000
@@ -0,0 +1,18 @@
+/*
+ * The function implemented in this module is an aid for AMR-EFR interworking;
+ * it is meant to be invoked directly after amr_encode_frame().  It checks
+ * the encoder output for MR122 DHF and turns it into EFR DHF just like
+ * amr_dhf_subst_efr(), but only if the input PCM frame was an EHF.  This
+ * slightly more complicated logic is needed in order to replicate the observed
+ * behavior of AMR-EFR speech encoder in the extant GSM network of T-Mobile USA.
+ */
+
+#include "tw_amr.h"
+#include "namespace.h"
+#include "e_homing.h"
+
+void amr_dhf_subst_efr2(struct amr_param_frame *frame, const int16_t *pcm)
+{
+	if (encoder_homing_frame_test(pcm))
+		amr_dhf_subst_efr(frame);
+}