--channels: Allow common prefix in channel ranges.

Selecting a range of channels only works if the channel names are
purely numeric, but not if they have a common, non-numeric
prefix (eg as in "D0", "D1", ..).

This patch allows to use such channels in ranges by checking for
a common prefix. The syntax to for example select channels "D2"
through to "D5" is "D2-5".

Also adjust the manpage to include the new syntax and fix the
example that actually didn't work as the fx2lafw driver uses
"D0", "D1", ... as channel names.

doc/sigrok-cli.1

@@ -181,13 +181,15 @@ The default is to use all the channels available on a device. You can name
 a channel like this:
 .BR "1=CLK" .
 A range of channels can also be given, in the form
-.BR "1\-5" .
+.BR "1\-5"
+or (if they have a common prefix)
+.BR "CH1\-5" .
 .sp
 Example:
 .sp
 .RB "  $ " "sigrok\-cli \-\-driver fx2lafw \-\-samples 100"
 .br
-.B "               \-\-channels 1=CLK,2\-4,7"
+.B "               \-\-channels D1=CLK,D2\-4,D7"
 .br
  CLK:11111111 11111111 11111111 11111111 [...]
    2:11111111 11111111 11111111 11111111 [...]

parsers.c

@@ -18,6 +18,7 @@
  */
 
 #include <config.h>
+#include <ctype.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
@@ -45,8 +46,8 @@ GSList *parse_channelstring(struct sr_dev_inst *sdi, const char *channelstring)
 {
 	struct sr_channel *ch;
 	GSList *channellist, *channels;
-	int ret, n, b, e, i;
-	char **tokens, **range, **names, *eptr, str[8];
+	int ret, n, b, e, i, plen;
+	char **tokens, **range, **names, *sptr, *eptr, str[8];
 
 	channels = sr_dev_inst_channels_get(sdi);
 
@@ -89,9 +90,9 @@ GSList *parse_channelstring(struct sr_dev_inst *sdi, const char *channelstring)
 		} else if (strchr(names[0], '-')) {
 			/*
 			 * A range of channels in the form a-b. This will only work
-			 * if the channels are named as numbers -- so every channel
-			 * in the range must exist as a channel name string in the
-			 * device.
+			 * if the channels are named as numbers (with an optional prefix)
+			 * -- so every channel in the range must exist as a channel name
+			 * string in the device.
 			 */
 			if (names[1]) {
 				/* Channel range syntax not allowed when renaming. */
@@ -108,15 +109,28 @@ GSList *parse_channelstring(struct sr_dev_inst *sdi, const char *channelstring)
 				goto range_fail;
 			}
 
+			/* Find start of numeric range (first digit) in range string. */
+			for (sptr = names[0]; *sptr != '-' && !isdigit(*sptr); sptr++);
+			if (*sptr == '-') { /* no digit found before range separator. */
+				g_critical("Channel range '%s' needs numbered channels.", names[0]);
+				ret = SR_ERR;
+				goto range_fail;
+			}
+
+			/* Length of channel name prefix. */
+			plen = sptr - names[0];
+
+			range = g_strsplit(sptr, "-", 2);
+
 			b = strtol(range[0], &eptr, 10);
 			if (eptr == range[0] || *eptr != '\0') {
-				g_critical("Invalid channel '%s'.", range[0]);
+				g_critical("Invalid channel '%.*s%s'.", plen, names[0], range[0]);
 				ret = SR_ERR;
 				goto range_fail;
 			}
 			e = strtol(range[1], NULL, 10);
 			if (eptr == range[1] || *eptr != '\0') {
-				g_critical("Invalid channel '%s'.", range[1]);
+				g_critical("Invalid channel '%.*s%s'.", plen, names[0], range[1]);
 				ret = SR_ERR;
 				goto range_fail;
 			}
@@ -127,15 +141,15 @@ GSList *parse_channelstring(struct sr_dev_inst *sdi, const char *channelstring)
 			}
 
 			while (b <= e) {
-				n = snprintf(str, 8, "%d", b);
+				n = snprintf(str, 8, "%.*s%d", plen, names[0], b);
 				if (n < 0 || n > 8) {
-					g_critical("Invalid channel '%d'.", b);
+					g_critical("Invalid channel '%.*s%d'.", plen, names[0], b);
 					ret = SR_ERR;
 					break;
 				}
 				ch = find_channel(channels, str);
 				if (!ch) {
-					g_critical("unknown channel '%d'.", b);
+					g_critical("unknown channel '%s'.", str);
 					ret = SR_ERR;
 					break;
 				}