--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtest/parse_dlcap.c	Tue Dec 13 07:03:55 2022 +0000
@@ -0,0 +1,54 @@
+/*
+ * All TCH/F downlink capture files produced by fc-shell tch record
+ * (both FR and EFR, both old and new formats) include the same
+ * 81-character block in each line: 3 DSP status words followed by
+ * 33 bytes of frame data.  Here we are factoring out the function
+ * for parsing this common part.
+ */
+
+#include <ctype.h>
+#include <stdint.h>
+
+static
+decode_hex_digit(ch)
+{
+	if (isdigit(ch))
+		return(ch - '0');
+	else if (isupper(ch))
+		return(ch - 'A' + 10);
+	else
+		return(ch - 'a' + 10);
+}
+
+parse_dlcap_common(line, status_words, tidsp_bytes)
+	char *line;
+	uint16_t *status_words;
+	uint8_t *tidsp_bytes;
+{
+	char *cp;
+	int i;
+
+	/* grok DSP status words */
+	cp = line;
+	for (i = 0; i < 3; i++) {
+		if (!isxdigit(cp[0]) || !isxdigit(cp[1]) ||
+		    !isxdigit(cp[2]) || !isxdigit(cp[3]))
+			return -1;
+		status_words[i] = (decode_hex_digit(cp[0]) << 12) |
+				  (decode_hex_digit(cp[1]) << 8) |
+				  (decode_hex_digit(cp[2]) << 4) |
+				   decode_hex_digit(cp[3]);
+		cp += 4;
+		if (*cp++ != ' ')
+			return -1;
+	}
+	/* read the frame bits */
+	for (i = 0; i < 33; i++) {
+		if (!isxdigit(cp[0]) || !isxdigit(cp[1]))
+			return -1;
+		tidsp_bytes[i] = (decode_hex_digit(cp[0]) << 4) |
+				  decode_hex_digit(cp[1]);
+		cp += 2;
+	}
+	return 0;
+}