--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libgsmfr2/pack_frame.c	Fri Apr 12 22:30:24 2024 +0000
@@ -0,0 +1,52 @@
+/*
+ * This module holds our gsmfr_pack_frame() function: packing a single GSM-FR
+ * frame from a struct of broken-down parameters into libgsm/RTP format.
+ */
+
+#include <stdint.h>
+#include "tw_gsmfr.h"
+
+#define	GSM_FR_MAGIC	0xD
+
+void gsmfr_pack_frame(const struct gsmfr_param_frame *param, uint8_t *frame)
+{
+	uint8_t *c = frame;
+	unsigned sub;
+
+	*c++ =   (GSM_FR_MAGIC << 4)
+	       | ((param->LARc[0] >> 2) & 0xF);
+	*c++ =   ((param->LARc[0] & 0x3) << 6)
+	       | (param->LARc[1] & 0x3F);
+	*c++ =   ((param->LARc[2] & 0x1F) << 3)
+	       | ((param->LARc[3] >> 2) & 0x7);
+	*c++ =   ((param->LARc[3] & 0x3) << 6)
+	       | ((param->LARc[4] & 0xF) << 2)
+	       | ((param->LARc[5] >> 2) & 0x3);
+	*c++ =   ((param->LARc[5] & 0x3) << 6)
+	       | ((param->LARc[6] & 0x7) << 3)
+	       | (param->LARc[7] & 0x7);
+	for (sub = 0; sub < 4; sub++) {
+		*c++ =   ((param->Nc[sub] & 0x7F) << 1)
+		       | ((param->bc[sub] >> 1) & 0x1);
+		*c++ =   ((param->bc[sub] & 0x1) << 7)
+		       | ((param->Mc[sub] & 0x3) << 5)
+		       | ((param->xmaxc[sub] >> 1) & 0x1F);
+		*c++ =   ((param->xmaxc[sub] & 0x1) << 7)
+		       | ((param->xMc[sub][0] & 0x7) << 4)
+		       | ((param->xMc[sub][1] & 0x7) << 1)
+		       | ((param->xMc[sub][2] >> 2) & 0x1);
+		*c++ =   ((param->xMc[sub][2] & 0x3) << 6)
+		       | ((param->xMc[sub][3] & 0x7) << 3)
+		       | (param->xMc[sub][4] & 0x7);
+		*c++ =   ((param->xMc[sub][5] & 0x7) << 5)
+		       | ((param->xMc[sub][6] & 0x7) << 2)
+		       | ((param->xMc[sub][7] >> 1) & 0x3);
+		*c++ =   ((param->xMc[sub][7] & 0x1) << 7)
+		       | ((param->xMc[sub][8] & 0x7) << 4)
+		       | ((param->xMc[sub][9] & 0x7) << 1)
+		       | ((param->xMc[sub][10] >> 2) & 0x1);
+		*c++ =   ((param->xMc[sub][10] & 0x3) << 6)
+		       | ((param->xMc[sub][11] & 0x7) << 3)
+		       | (param->xMc[sub][12] & 0x7);
+	}
+}