Do What I Mean when the user asks for random integers or characters.

Up to now jot would fail to generate the last character in the range
or skew the integer distribution in a way that would generate the numbers
in the range's limits with half the probability of the rest.

This modification fixes the program, rather than documenting the
strange behavior, as suggested in docs/54879.

Also, correctly specify the range of random(3).

PR:		docs/54879
MFC after:	2 weeks

2 files changed, 50 insertions, 8 deletions

diff --git a/usr.bin/jot/jot.1 b/usr.bin/jot/jot.1
index e1e98ac..1aa0d62 100644
--- a/usr.bin/jot/jot.1
+++ b/usr.bin/jot/jot.1
@@ -32,7 +32,7 @@
 .\"	@(#)jot.1	8.1 (Berkeley) 6/6/93
 .\" $FreeBSD$
 .\"
-.Dd June 6, 1993
+.Dd November 6, 2006
 .Dt JOT 1
 .Os
 .Sh NAME
@@ -145,6 +145,23 @@ when no seed is specified,
 and through
 .Xr random 3
 when a seed is given.
+When
+.Nm
+is asked to generate random integers or characters with begin
+and end values in the range of the random number generator function
+and no format is specified with one of the
+.Fl w ,
+.Fl b ,
+or
+.Fl p
+options,
+.Nm
+will arrange for all the values in the range to appear in the output
+with an equal probability.
+In all other cases be careful to ensure that the output format's
+rounding or truncation will not skew the distribution of output
+values in an unintended way.
+.Pp
 The name
 .Nm
 derives in part from
diff --git a/usr.bin/jot/jot.c b/usr.bin/jot/jot.c
index 1464e4d..d7f700c 100644
--- a/usr.bin/jot/jot.c
+++ b/usr.bin/jot/jot.c
@@ -103,7 +103,9 @@ main(int argc, char **argv)
 	unsigned int	mask = 0;
 	int	n = 0;
 	int	ch;
-	bool	have_seed = false;
+	bool	use_random = false;
+	bool	have_format = false;
+	double	divisor;
 
 	while ((ch = getopt(argc, argv, "rb:w:cs:np:")) != -1)
 		switch (ch) {
@@ -123,6 +125,7 @@ main(int argc, char **argv)
 			if (strlcpy(format, optarg, sizeof(format)) >=
 			    sizeof(format))
 				errx(1, "-%c word too long", ch);
+			have_format = true;
 			break;
 		case 's':
 			sepstring = optarg;
@@ -131,6 +134,7 @@ main(int argc, char **argv)
 			prec = atoi(optarg);
 			if (prec <= 0)
 				errx(1, "bad precision value");
+			have_format = true;
 			break;
 		default:
 			usage();
@@ -145,7 +149,7 @@ main(int argc, char **argv)
 				errx(1, "bad s value: %s", argv[3]);
 			mask |= HAVE_STEP;
 			if (randomize)
-				have_seed = true;
+				use_random = true;
 		}
 		/* FALLTHROUGH */
 	case 3:
@@ -258,14 +262,35 @@ main(int argc, char **argv)
 	if (reps == 0)
 		infinity = 1;
 	if (randomize) {
-		x = (ender - begin) * (ender > begin ? 1 : -1);
-		if (have_seed)
+		if (use_random) {
 			srandom((unsigned long)s);
+			divisor = (double)INT32_MAX + 1;
+		} else
+			divisor = (double)UINT32_MAX + 1;
+
+		/*
+		 * Attempt to DWIM when the user has specified an
+		 * integer range within that of the random number
+		 * generator: distribute the numbers equally in
+		 * the range [begin .. ender].  Jot's default %.0f
+		 * format would make the appearance of the first and
+		 * last specified value half as likely as the rest.
+		 */
+		if (!have_format && prec == 0 &&
+		    begin >= 0 && begin < divisor &&
+		    ender >= 0 && ender < divisor) {
+			ender += 1;
+			nosign = 1;
+			intdata = 1;
+			(void)strlcpy(format,
+			    chardata ? "%c" : "%u", sizeof(format));
+		}
+		x = (ender - begin) * (ender > begin ? 1 : -1);
 		for (i = 1; i <= reps || infinity; i++) {
-			if (have_seed)
-				y = random() / ((double)LONG_MAX + 1);
+			if (use_random)
+				y = random() / divisor;
 			else
-				y = arc4random() / ((double)UINT32_MAX + 1);
+				y = arc4random() / divisor;
 			if (putdata(y * x + begin, reps - i))
 				errx(1, "range error in conversion");
 		}