--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtwamr/dhf_subst.c	Wed May 08 00:27:51 2024 +0000
@@ -0,0 +1,21 @@
+/*
+ * 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 if the generated frame exactly
+ * matches MR122 DHF, it is changed to GSM-EFR DHF.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include "tw_amr.h"
+
+void amr_dhf_subst_efr(struct amr_param_frame *frame)
+{
+	if (frame->type != TX_SPEECH_GOOD)
+		return;
+	if (frame->mode != MR122)
+		return;
+	if (memcmp(frame->param, amr_dhf_mr122, AMR_MAX_PRM * sizeof(int16_t)))
+		return;
+	memcpy(frame->param, amr_dhf_gsmefr, AMR_MAX_PRM * sizeof(int16_t));
+}