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Streamline and refactor the code a bit more:

There are two sentinels for infinite output: infinity == true and reps == 0.
Ensure that infinity is set to true whenever reps is set to zero, then we
can always use 'if (infinity)'.

This allows us to merge the loop for deterministic output into the first
if (!randomize) statement, which is a lot tidier.

Insert an occasional empty line.

"move fast and break stuff" tedu

/*	$OpenBSD: jot.c,v 1.35 2016/08/16 16:49:24 tb Exp $	*/
/*	$NetBSD: jot.c,v 1.3 1994/12/02 20:29:43 pk Exp $	*/

/*-
 * Copyright (c) 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * jot - print sequential or random data
 *
 * Author:  John Kunze, Office of Comp. Affairs, UCB
 */

#include <err.h>
#include <stdbool.h>
#include <ctype.h>
#include <limits.h>
#include <math.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define	REPS_DEF	100
#define	BEGIN_DEF	1
#define	ENDER_DEF	100
#define	STEP_DEF	1

#define	STEP		1
#define	ENDER		2
#define	BEGIN		4
#define	REPS		8

#define	is_default(s)	(strcmp((s), "-") == 0)

static double	begin = BEGIN_DEF;
static double	ender = ENDER_DEF;
static double	step = STEP_DEF;
static long	reps = REPS_DEF;
static bool	randomize;
static bool	infinity;
static bool	boring;
static int	prec = -1;
static bool	intdata;
static bool	longdata;
static bool	chardata;
static bool	nosign;
static bool	finalnl = true;
static char	sepstring[BUFSIZ] = "\n";
static char	format[BUFSIZ];

static void	getformat(void);
static int	getprec(char *);
static int	putdata(double, bool);
static void __dead	usage(void);

int
main(int argc, char *argv[])
{
	double		x;
	double		y;
	long		i;
	unsigned int	mask = 0;
	int		n = 0;
	int		ch;
	const	char	*errstr;

	if (pledge("stdio", NULL) == -1)
		err(1, "pledge");

	while ((ch = getopt(argc, argv, "rb:w:cs:np:")) != -1)
		switch (ch) {
		case 'r':
			randomize = true;
			break;
		case 'c':
			chardata = true;
			break;
		case 'n':
			finalnl = false;
			break;
		case 'b':
			boring = true;
			if (strlcpy(format, optarg, sizeof(format)) >=
			    sizeof(format))
				errx(1, "-b word too long");
			break;
		case 'w':
			if (strlcpy(format, optarg, sizeof(format)) >=
			    sizeof(format))
				errx(1, "-w word too long");
			break;
		case 's':
			if (strlcpy(sepstring, optarg, sizeof(sepstring)) >=
			    sizeof(sepstring))
				errx(1, "-s string too long");
			break;
		case 'p':
			prec = strtonum(optarg, 0, INT_MAX, &errstr);
			if (errstr != NULL)
				errx(1, "bad precision value, %s: %s", errstr,
					optarg);
			break;
		default:
			usage();
		}
	argc -= optind;
	argv += optind;

	switch (argc) {	/* examine args right to left, falling thru cases */
	case 4:
		if (!is_default(argv[3])) {
			if (!sscanf(argv[3], "%lf", &step))
				errx(1, "Bad s value:  %s", argv[3]);
			mask |= STEP;
			if (randomize)
				warnx("random seeding not supported");
		}
	case 3:
		if (!is_default(argv[2])) {
			if (!sscanf(argv[2], "%lf", &ender))
				ender = argv[2][strlen(argv[2])-1];
			mask |= ENDER;
			if (prec == -1)
				n = getprec(argv[2]);
		}
	case 2:
		if (!is_default(argv[1])) {
			if (!sscanf(argv[1], "%lf", &begin))
				begin = argv[1][strlen(argv[1])-1];
			mask |= BEGIN;
			if (prec == -1)
				prec = getprec(argv[1]);
			if (n > prec)		/* maximum precision */
				prec = n;
		}
	case 1:
		if (!is_default(argv[0])) {
			if (!sscanf(argv[0], "%ld", &reps))
				errx(1, "Bad reps value:  %s", argv[0]);
			mask |= REPS;
			if (reps == 0)
				infinity = true;
			if (prec == -1)
				prec = 0;
		}
		break;
	case 0:
		usage();
		break;
	default:
		errx(1, "Too many arguments.  What do you mean by %s?",
		    argv[4]);
	}

	getformat();

	if (!randomize) {
		/*
		 * Consolidate the values of reps, begin, ender, step:
		 * The formula ender - begin == (reps - 1) * step shows that any
		 * three determine the fourth (unless reps == 1 or step == 0).
		 * The manual states the following rules:
		 * 1. If four are specified, compare the given and the computed
		 *    value of reps and take the smaller of the two.
		 * 2. If steps was omitted, it takes the default, unless both
		 *    begin and ender were specified.
		 * 3. Assign defaults to omitted values for reps, begin, ender,
		 *    from left to right.
		 */
		switch (mask) { /* Four cases involve both begin and ender. */
		case REPS | BEGIN | ENDER | STEP:
			if (infinity)
				errx(1,
				    "Can't specify end of infinite sequence");
			if (step != 0.0) {
				long t = (ender - begin + step) / step;
				if (t <= 0)
					errx(1, "Impossible stepsize");
				if (t < reps)
					reps = t;
			}
			break;
		case REPS | BEGIN | ENDER:
			if (infinity)
				errx(1,
				    "Can't specify end of infinite sequence");
			if (reps == 1)
				step = 0.0;
			else
				step = (ender - begin) / (reps - 1);
			break;
		case BEGIN | ENDER:
			step = ender > begin ? 1 : -1; /* FreeBSD's behavior. */
			/* FALLTHROUGH */
		case BEGIN | ENDER | STEP:
			if (step == 0.0) {
				reps = 0;
				infinity = true;
				break;
			}
			reps = (ender - begin + step) / step;
			if (reps <= 0)
				errx(1, "Impossible stepsize");
			break;
		case ENDER:		/* Four cases involve only ender. */
		case ENDER | STEP:
		case REPS | ENDER:
		case REPS | ENDER | STEP:
			if (infinity)
				errx(1,
				    "Must specify start of infinite sequence");
			begin = ender - reps * step + step;
			break;
		default:
			/*
			 * The remaining eight cases omit ender.  We don't need
			 * to compute anything because only reps, begin, step
			 * are used for producing output below.  Rules 2. and 3.
			 * together imply that ender will be set last.
			 */
			break;
		}

		for (i = 1, x = begin; i <= reps || infinity; i++, x += step)
			if (putdata(x, reps == i && !infinity))
				errx(1, "range error in conversion: %f", x);
	} else { /* Random output: use defaults for omitted values. */
		bool		use_unif;
		uint32_t	pow10 = 1;
		uint32_t	uintx = 0; /* Initialized to make gcc happy. */

		if (prec > 9)	/* pow(10, prec) > UINT32_MAX */
			errx(1, "requested precision too large");

		if (ender < begin) {
			x = begin;
			begin = ender;
			ender = x;
		}
		x = ender - begin;

		if (prec == 0 && (fmod(ender, 1) != 0 || fmod(begin, 1) != 0))
			use_unif = 0;
		else {
			while (prec-- > 0)
				pow10 *= 10;
			/*
			 * If pow10 * (ender - begin) is an integer, use
			 * arc4random_uniform().
			 */
			use_unif = fmod(pow10 * (ender - begin), 1) == 0;
			if (use_unif) {
				uintx = pow10 * (ender - begin);
				if (uintx >= UINT32_MAX)
					errx(1, "requested range too large");
				uintx++;
			}
		}

		for (i = 1; i <= reps || infinity; i++) {
			double v;

			if (use_unif) {
				y = arc4random_uniform(uintx) / (double)pow10;
				v = y + begin;
			} else {
				y = arc4random() / ((double)0xffffffff + 1);
				v = y * x + begin;
			}
			if (putdata(v, reps == i && !infinity))
				errx(1, "range error in conversion: %f", v);
		}
	}

	if (finalnl)
		putchar('\n');

	return (0);
}

static int
putdata(double x, bool last)
{
	if (boring)
		printf("%s", format);
	else if (longdata && nosign) {
		if (x <= (double)ULONG_MAX && x >= 0.0)
			printf(format, (unsigned long)x);
		else
			return (1);
	} else if (longdata) {
		if (x <= (double)LONG_MAX && x >= (double)LONG_MIN)
			printf(format, (long)x);
		else
			return (1);
	} else if (chardata || (intdata && !nosign)) {
		if (x <= (double)INT_MAX && x >= (double)INT_MIN)
			printf(format, (int)x);
		else
			return (1);
	} else if (intdata) {
		if (x <= (double)UINT_MAX && x >= 0.0)
			printf(format, (unsigned int)x);
		else
			return (1);
	} else
		printf(format, x);
	if (!last)
		fputs(sepstring, stdout);

	return (0);
}

static void __dead
usage(void)
{
	(void)fprintf(stderr, "usage: jot [-cnr] [-b word] [-p precision] "
	    "[-s string] [-w word]\n"
	    "	   [reps [begin [end [s]]]]\n");
	exit(1);
}

static int
getprec(char *s)
{
	if ((s = strchr(s, '.')) == NULL)
		return (0);
	return (strspn(s + 1, "0123456789"));
}

static void
getformat(void)
{
	char	*p, *p2;
	int dot, hash, space, sign, numbers = 0;
	size_t sz;

	if (boring)				/* no need to bother */
		return;
	for (p = format; *p != '\0'; p++)	/* look for '%' */
		if (*p == '%') {
			if (*(p+1) != '%')
				break;
			p++;			/* leave %% alone */
		}
	sz = sizeof(format) - strlen(format) - 1;
	if (*p == '\0' && !chardata) {
		int n;

		n = snprintf(p, sz, "%%.%df", prec);
		if (n == -1 || n >= (int)sz)
			errx(1, "-w word too long");
	} else if (*p == '\0' && chardata) {
		if (strlcpy(p, "%c", sz) >= sz)
			errx(1, "-w word too long");
		intdata = true;
	} else if (*(p+1) == '\0') {
		if (sz <= 0)
			errx(1, "-w word too long");
		/* cannot end in single '%' */
		strlcat(format, "%", sizeof format);
	} else {
		/*
		 * Allow conversion format specifiers of the form
		 * %[#][ ][{+,-}][0-9]*[.[0-9]*]? where ? must be one of
		 * [l]{d,i,o,u,x} or {f,e,g,E,G,d,o,x,D,O,U,X,c,u}
		 */
		p2 = p++;
		dot = hash = space = sign = numbers = 0;
		while (!isalpha((unsigned char)*p)) {
			if (isdigit((unsigned char)*p)) {
				numbers++;
				p++;
			} else if ((*p == '#' && !(numbers|dot|sign|space|
			    hash++)) ||
			    (*p == ' ' && !(numbers|dot|space++)) ||
			    ((*p == '+' || *p == '-') && !(numbers|dot|sign++))
			    || (*p == '.' && !(dot++)))
				p++;
			else
				goto fmt_broken;
		}
		if (*p == 'l') {
			longdata = true;
			if (*++p == 'l') {
				if (p[1] != '\0')
					p++;
				goto fmt_broken;
			}
		}
		switch (*p) {
		case 'o': case 'u': case 'x': case 'X':
			intdata = nosign = true;
			break;
		case 'd': case 'i':
			intdata = true;
			break;
		case 'D':
			if (!longdata) {
				intdata = true;
				break;
			}
		case 'O': case 'U':
			if (!longdata) {
				intdata = nosign = true;
				break;
			}
		case 'c':
			if (!(intdata | longdata)) {
				chardata = true;
				break;
			}
		case 'h': case 'n': case 'p': case 'q': case 's': case 'L':
		case '$': case '*':
			goto fmt_broken;
		case 'f': case 'e': case 'g': case 'E': case 'G':
			if (!longdata)
				break;
			/* FALLTHROUGH */
		default:
fmt_broken:
			*++p = '\0';
			errx(1, "illegal or unsupported format '%s'", p2);
			/* NOTREACHED */
		}
		while (*++p != '\0')
			if (*p == '%' && *(p+1) != '\0' && *(p+1) != '%')
				errx(1, "too many conversions");
			else if (*p == '%' && *(p+1) == '%')
				p++;
			else if (*p == '%' && *(p+1) == '\0') {
				strlcat(format, "%", sizeof format);
				break;
			}
	}
}