1 /* $OpenBSD: arithmetic.c,v 1.28 2018/12/27 17:27:23 tedu Exp $ */
2
3 /*
4 * Copyright (c) 1989, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Eamonn McManus of Trinity College Dublin.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. Neither the name of the University nor the names of its contributors
19 * may be used to endorse or promote products derived from this software
20 * without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35 /*
36 * By Eamonn McManus, Trinity College Dublin <emcmanus@cs.tcd.ie>.
37 *
38 * The operation of this program mimics that of the standard Unix game
39 * `arithmetic'. I've made it as close as I could manage without examining
40 * the source code. The principal differences are:
41 *
42 * The method of biasing towards numbers that had wrong answers in the past
43 * is different; original `arithmetic' seems to retain the bias forever,
44 * whereas this program lets the bias gradually decay as it is used.
45 *
46 * Original `arithmetic' delays for some period (3 seconds?) after printing
47 * the score. I saw no reason for this delay, so I scrapped it.
48 *
49 * There is no longer a limitation on the maximum range that can be supplied
50 * to the program. The original program required it to be less than 100.
51 * Anomalous results may occur with this program if ranges big enough to
52 * allow overflow are given.
53 *
54 * I have obviously not attempted to duplicate bugs in the original. It
55 * would go into an infinite loop if invoked as `arithmetic / 0'. It also
56 * did not recognise an EOF in its input, and would continue trying to read
57 * after it. It did not check that the input was a valid number, treating any
58 * garbage as 0. Finally, it did not flush stdout after printing its prompt,
59 * so in the unlikely event that stdout was not a terminal, it would not work
60 * properly.
61 */
62
63 #include <err.h>
64 #include <ctype.h>
65 #include <limits.h>
66 #include <signal.h>
67 #include <stdio.h>
68 #include <stdlib.h>
69 #include <string.h>
70 #include <time.h>
71 #include <unistd.h>
72
73 int getrandom(uint32_t, int, int);
74 __dead void intr(int);
75 int opnum(int);
76 void penalise(int, int, int);
77 int problem(void);
78 void showstats(void);
79 __dead void usage(void);
80
81 const char keylist[] = "+-x/";
82 const char defaultkeys[] = "+-";
83 const char *keys = defaultkeys;
84 int nkeys = sizeof(defaultkeys) - 1;
85 uint32_t rangemax = 10;
86 int nright, nwrong;
87 time_t qtime;
88 #define NQUESTS 20
89
90 /*
91 * Select keys from +-x/ to be asked addition, subtraction, multiplication,
92 * and division problems. More than one key may be given. The default is
93 * +-. Specify a range to confine the operands to 0 - range. Default upper
94 * bound is 10. After every NQUESTS questions, statistics on the performance
95 * so far are printed.
96 */
97 int
main(int argc,char * argv[])98 main(int argc, char *argv[])
99 {
100 int ch, cnt;
101 const char *errstr;
102
103 if (pledge("stdio", NULL) == -1)
104 err(1, "pledge");
105
106 while ((ch = getopt(argc, argv, "hr:o:")) != -1)
107 switch(ch) {
108 case 'o': {
109 const char *p;
110
111 for (p = keys = optarg; *p; ++p)
112 if (!strchr(keylist, *p))
113 errx(1, "unknown key.");
114 nkeys = p - optarg;
115 break;
116 }
117 case 'r':
118 rangemax = strtonum(optarg, 1, (1ULL<<31)-1, &errstr);
119 if (errstr)
120 errx(1, "invalid range, %s: %s", errstr, optarg);
121 break;
122 case 'h':
123 default:
124 usage();
125 }
126 if (argc -= optind)
127 usage();
128
129 (void)signal(SIGINT, intr);
130
131 /* Now ask the questions. */
132 for (;;) {
133 for (cnt = NQUESTS; cnt--;)
134 if (problem() == EOF)
135 intr(0); /* Print score and exit */
136 showstats();
137 }
138 }
139
140 /* Handle interrupt character. Print score and exit. */
141 void
intr(int dummy)142 intr(int dummy)
143 {
144 showstats();
145 _exit(0);
146 }
147
148 /* Print score. Original `arithmetic' had a delay after printing it. */
149 void
showstats(void)150 showstats(void)
151 {
152 if (nright + nwrong > 0) {
153 (void)printf("\n\nRights %d; Wrongs %d; Score %d%%",
154 nright, nwrong, (int)(100L * nright / (nright + nwrong)));
155 if (nright > 0)
156 (void)printf("\nTotal time %ld seconds; %.1f seconds per problem\n\n",
157 (long)qtime, (float)qtime / nright);
158 }
159 (void)printf("\n");
160 }
161
162 /*
163 * Pick a problem and ask it. Keeps asking the same problem until supplied
164 * with the correct answer, or until EOF or interrupt is typed. Problems are
165 * selected such that the right operand and either the left operand (for +, x)
166 * or the correct result (for -, /) are in the range 0 to rangemax. Each wrong
167 * answer causes the numbers in the problem to be penalised, so that they are
168 * more likely to appear in subsequent problems.
169 */
170 int
problem(void)171 problem(void)
172 {
173 char *p;
174 time_t start, finish;
175 int left, op, right, result;
176 char line[80];
177
178 op = keys[arc4random_uniform(nkeys)];
179 if (op != '/')
180 right = getrandom(rangemax + 1, op, 1);
181 retry:
182 /* Get the operands. */
183 switch (op) {
184 case '+':
185 left = getrandom(rangemax + 1, op, 0);
186 result = left + right;
187 break;
188 case '-':
189 result = getrandom(rangemax + 1, op, 0);
190 left = right + result;
191 break;
192 case 'x':
193 left = getrandom(rangemax + 1, op, 0);
194 result = left * right;
195 break;
196 case '/':
197 right = getrandom(rangemax, op, 1) + 1;
198 result = getrandom(rangemax + 1, op, 0);
199 left = right * result + arc4random_uniform(right);
200 break;
201 }
202
203 /*
204 * A very big maxrange could cause negative values to pop
205 * up, owing to overflow.
206 */
207 if (result < 0 || left < 0)
208 goto retry;
209
210 (void)printf("%d %c %d = ", left, op, right);
211 (void)fflush(stdout);
212 (void)time(&start);
213
214 /*
215 * Keep looping until the correct answer is given, or until EOF or
216 * interrupt is typed.
217 */
218 for (;;) {
219 if (!fgets(line, sizeof(line), stdin)) {
220 (void)printf("\n");
221 return(EOF);
222 }
223 for (p = line; isspace((unsigned char)*p); ++p);
224 if (!isdigit((unsigned char)*p)) {
225 (void)printf("Please type a number.\n");
226 continue;
227 }
228 if (atoi(p) == result) {
229 (void)printf("Right!\n");
230 ++nright;
231 break;
232 }
233 /* Wrong answer; penalise and ask again. */
234 (void)printf("What?\n");
235 ++nwrong;
236 penalise(right, op, 1);
237 if (op == 'x' || op == '+')
238 penalise(left, op, 0);
239 else
240 penalise(result, op, 0);
241 }
242
243 /*
244 * Accumulate the time taken. Obviously rounding errors happen here;
245 * however they should cancel out, because some of the time you are
246 * charged for a partially elapsed second at the start, and some of
247 * the time you are not charged for a partially elapsed second at the
248 * end.
249 */
250 (void)time(&finish);
251 qtime += finish - start;
252 return(0);
253 }
254
255 /*
256 * Here is the code for accumulating penalties against the numbers for which
257 * a wrong answer was given. The right operand and either the left operand
258 * (for +, x) or the result (for -, /) are stored in a list for the particular
259 * operation, and each becomes more likely to appear again in that operation.
260 * Initially, each number is charged a penalty of WRONGPENALTY, giving it that
261 * many extra chances of appearing. Each time it is selected because of this,
262 * its penalty is decreased by one; it is removed when it reaches 0.
263 *
264 * The penalty[] array gives the sum of all penalties in the list for
265 * each operation and each operand. The penlist[] array has the lists of
266 * penalties themselves.
267 */
268
269 uint32_t penalty[sizeof(keylist) - 1][2];
270 struct penalty {
271 int value; /* Penalised value. */
272 uint32_t penalty; /* Its penalty. */
273 struct penalty *next;
274 } *penlist[sizeof(keylist) - 1][2];
275
276 #define WRONGPENALTY 5 /* Perhaps this should depend on maxrange. */
277
278 /*
279 * Add a penalty for the number `value' to the list for operation `op',
280 * operand number `operand' (0 or 1). If we run out of memory, we just
281 * forget about the penalty (how likely is this, anyway?).
282 */
283 void
penalise(int value,int op,int operand)284 penalise(int value, int op, int operand)
285 {
286 struct penalty *p;
287
288 op = opnum(op);
289 if ((p = malloc(sizeof(*p))) == NULL)
290 return;
291 p->next = penlist[op][operand];
292 penlist[op][operand] = p;
293 penalty[op][operand] += p->penalty = WRONGPENALTY;
294 p->value = value;
295 }
296
297 /*
298 * Select a random value from 0 to maxval - 1 for operand `operand' (0 or 1)
299 * of operation `op'. The random number we generate is either used directly
300 * as a value, or represents a position in the penalty list. If the latter,
301 * we find the corresponding value and return that, decreasing its penalty.
302 */
303 int
getrandom(uint32_t maxval,int op,int operand)304 getrandom(uint32_t maxval, int op, int operand)
305 {
306 uint32_t value;
307 struct penalty **pp, *p;
308
309 op = opnum(op);
310 value = arc4random_uniform(maxval + penalty[op][operand]);
311
312 /*
313 * 0 to maxval - 1 is a number to be used directly; bigger values
314 * are positions to be located in the penalty list.
315 */
316 if (value < maxval)
317 return((int)value);
318 value -= maxval;
319
320 /*
321 * Find the penalty at position `value'; decrement its penalty and
322 * delete it if it reaches 0; return the corresponding value.
323 */
324 for (pp = &penlist[op][operand]; (p = *pp) != NULL; pp = &p->next) {
325 if (p->penalty > value) {
326 value = p->value;
327 penalty[op][operand]--;
328 if (--(p->penalty) <= 0) {
329 p = p->next;
330 (void)free((char *)*pp);
331 *pp = p;
332 }
333 return(value);
334 }
335 value -= p->penalty;
336 }
337 /*
338 * We can only get here if the value from the penalty[] array doesn't
339 * correspond to the actual sum of penalties in the list. Provide an
340 * obscure message.
341 */
342 errx(1, "bug: inconsistent penalties.");
343 }
344
345 /* Return an index for the character op, which is one of [+-x/]. */
346 int
opnum(int op)347 opnum(int op)
348 {
349 char *p;
350
351 if (op == 0 || (p = strchr(keylist, op)) == NULL)
352 errx(1, "bug: op %c not in keylist %s.", op, keylist);
353 return(p - keylist);
354 }
355
356 /* Print usage message and quit. */
357 void
usage(void)358 usage(void)
359 {
360 extern char *__progname;
361 (void)fprintf(stderr, "usage: %s [-o +-x/] [-r range]\n", __progname);
362 exit(1);
363 }
364