--- a/.hgignore	Sun Nov 20 08:05:32 2022 +0000
+++ b/.hgignore	Sun Nov 20 08:30:07 2022 +0000
@@ -8,6 +8,7 @@
 ^frtest/gsmfr-cvt-dlcap$
 ^frtest/gsmfr-decode$
 ^frtest/gsmfr-encode$
+^frtest/gsmfr-preproc$
 
 ^miscutil/gsmrec-dump$
 

--- a/frtest/Makefile	Sun Nov 20 08:05:32 2022 +0000
+++ b/frtest/Makefile	Sun Nov 20 08:30:07 2022 +0000
@@ -1,6 +1,6 @@
 CC=	gcc
 CFLAGS=	-O2
-PROGS=	gsmfr-cvt-dlcap gsmfr-decode gsmfr-encode
+PROGS=	gsmfr-cvt-dlcap gsmfr-decode gsmfr-encode gsmfr-preproc
 LIBPP=	../libgsmfrp/libgsmfrp.a
 LIBTEST=../libtest/libtest.a
 LIBDEC=	${LIBTEST} ${LIBPP}
@@ -19,6 +19,9 @@
 gsmfr-encode:	encode.o ${LIBTEST}
 	${CC} ${CFLAGS} -o $@ encode.o ${LIBTEST} -lgsm
 
+gsmfr-preproc:	preproc.o ${LIBDEC}
+	${CC} ${CFLAGS} -o $@ preproc.o ${LIBDEC}
+
 install:
 	mkdir -p ${INSTBIN}
 	install -c ${PROGS} ${INSTBIN}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/frtest/preproc.c	Sun Nov 20 08:30:07 2022 +0000
@@ -0,0 +1,66 @@
+/*
+ * This utility reads an extended-libgsm file that may contain SID frames
+ * and BFI markers, passes it through our preprocessor and writes out
+ * pure libgsm frames.
+ */
+
+#include <stdio.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include "../libgsmfrp/gsm_fr_preproc.h"
+#include "../libtest/binreader.h"
+
+main(argc, argv)
+	char **argv;
+{
+	FILE *bini, *bino;
+	struct gsmfr_preproc_state *pp_state;
+	uint8_t frame[BINFILE_MAX_FRAME];
+	int rc, bfi, taf;
+
+	if (argc != 3) {
+		fprintf(stderr, "usage: %s input.gsm output.gsm\n", argv[0]);
+		exit(1);
+	}
+	bini = fopen(argv[1], "r");
+	if (!bini) {
+		perror(argv[1]);
+		exit(1);
+	}
+	bino = fopen(argv[2], "w");
+	if (!bino) {
+		perror(argv[2]);
+		exit(1);
+	}
+	pp_state = gsmfr_preproc_create();
+	if (!pp_state) {
+		fprintf(stderr, "gsmfr_preproc_create() failed!\n");
+		exit(1);
+	}
+	for (;;) {
+		rc = binfile_read_frame(bini, frame);
+		if (rc < 0) {
+			fprintf(stderr, "error: garbage in %s\n", argv[1]);
+			exit(1);
+		}
+		if (!rc)
+			break;
+		if (frame[0] == 0xBF) {
+			bfi = 1;
+			taf = frame[1] & 1;
+		} else if ((frame[0] & 0xF0) == 0xD0)
+			bfi = 0;
+		else {
+			fprintf(stderr, "error: %s is not in FR codec format\n",
+				argv[1]);
+			exit(1);
+		}
+		if (bfi)
+			gsmfr_preproc_bfi(pp_state, taf, frame);
+		else
+			gsmfr_preproc_good_frame(pp_state, frame);
+		fwrite(frame, 1, 33, bino);
+	}
+	fclose(bino);
+	exit(0);
+}