File: eval.c

package info (click to toggle)
ucpp 1.3.2-2
  • links: PTS
  • area: main
  • in suites: bullseye, buster, sid, stretch
  • size: 500 kB
  • ctags: 1,058
  • sloc: ansic: 7,997; makefile: 66
file content (699 lines) | stat: -rw-r--r-- 17,438 bytes parent folder | download | duplicates (5)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
/*
 * (c) Thomas Pornin 1999 - 2002
 *
 * 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.
 * 4. The name of the authors may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT 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 AUTHORS 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.
 *
 */

#include "tune.h"
#include <stdio.h>
#include <string.h>
#include <setjmp.h>
#include <limits.h>
#include "ucppi.h"
#include "mem.h"

JMP_BUF eval_exception;
long eval_line;
static int emit_eval_warnings;

/*
 * If you want to hardcode a conversion table, define a static array
 * of 256 int, and make transient_characters point to it.
 */
int *transient_characters = 0;

#define OCTAL(x)       ((x) >= '0' && (x) <= '7')
#define DECIM(x)       ((x) >= '0' && (x) <= '9')
#define HEXAD(x)       (DECIM(x) \
                       || (x) == 'a' || (x) == 'b' || (x) == 'c' \
                       || (x) == 'd' || (x) == 'e' || (x) == 'f' \
                       || (x) == 'A' || (x) == 'B' || (x) == 'C' \
                       || (x) == 'D' || (x) == 'E' || (x) == 'F')
#define OVAL(x)	       ((int)((x) - '0'))
#define DVAL(x)	       ((int)((x) - '0'))
#define HVAL(x)	       (DECIM(x) ? DVAL(x) \
                       : (x) == 'a' || (x) == 'A' ? 10 \
                       : (x) == 'b' || (x) == 'B' ? 11 \
                       : (x) == 'c' || (x) == 'C' ? 12 \
                       : (x) == 'd' || (x) == 'D' ? 13 \
                       : (x) == 'e' || (x) == 'E' ? 14 : 15)

#define ARITH_TYPENAME             big
#define ARITH_FUNCTION_HEADER      static inline

#define ARITH_ERROR(type)          z_error(type)
static void z_error(int type);

#ifdef ARITHMETIC_CHECKS
#define ARITH_WARNING(type)        z_warn(type)
static void z_warn(int type);
#endif

#include "arith.c"

static void z_error(int type)
{
	switch (type) {
	case ARITH_EXCEP_SLASH_D:
		error(eval_line, "division by 0");
		break;
	case ARITH_EXCEP_SLASH_O:
		error(eval_line, "overflow on division");
		break;
	case ARITH_EXCEP_PCT_D:
		error(eval_line, "division by 0 on modulus operator");
		break;
	case ARITH_EXCEP_CONST_O:
		error(eval_line, "constant too large for destination type");
		break;
#ifdef AUDIT
	default:
		ouch("erroneous integer error: %d", type);
#endif
	}
	throw(eval_exception);
}

#ifdef ARITHMETIC_CHECKS
static void z_warn(int type)
{
	switch (type) {
	case ARITH_EXCEP_CONV_O:
		warning(eval_line, "overflow on integer conversion");
		break;
	case ARITH_EXCEP_NEG_O:
		warning(eval_line, "overflow on unary minus");
		break;
	case ARITH_EXCEP_NOT_T:
		warning(eval_line,
			"bitwise inversion yields trap representation");
		break;
	case ARITH_EXCEP_PLUS_O:
		warning(eval_line, "overflow on addition");
		break;
	case ARITH_EXCEP_PLUS_U:
		warning(eval_line, "underflow on addition");
		break;
	case ARITH_EXCEP_MINUS_O:
		warning(eval_line, "overflow on subtraction");
		break;
	case ARITH_EXCEP_MINUS_U:
		warning(eval_line, "underflow on subtraction");
		break;
	case ARITH_EXCEP_AND_T:
		warning(eval_line,
			"bitwise AND yields trap representation");
		break;
	case ARITH_EXCEP_XOR_T:
		warning(eval_line,
			"bitwise XOR yields trap representation");
		break;
	case ARITH_EXCEP_OR_T:
		warning(eval_line,
			"bitwise OR yields trap representation");
		break;
	case ARITH_EXCEP_LSH_W:
		warning(eval_line, "left shift count greater than "
			"or equal to type width");
		break;
	case ARITH_EXCEP_LSH_C:
		warning(eval_line, "left shift count negative");
		break;
	case ARITH_EXCEP_LSH_O:
		warning(eval_line, "overflow on left shift");
		break;
	case ARITH_EXCEP_RSH_W:
		warning(eval_line, "right shift count greater than "
			"or equal to type width");
		break;
	case ARITH_EXCEP_RSH_C:
		warning(eval_line, "right shift count negative");
		break;
	case ARITH_EXCEP_RSH_N:
		warning(eval_line, "right shift of negative value");
		break;
	case ARITH_EXCEP_STAR_O:
		warning(eval_line, "overflow on multiplication");
		break;
	case ARITH_EXCEP_STAR_U:
		warning(eval_line, "underflow on multiplication");
		break;
#ifdef AUDIT
	default:
		ouch("erroneous integer warning: %d", type);
#endif
	}
}
#endif

typedef struct {
	int sign;
	union {
		u_big uv;
		s_big sv;
	} u;
} ppval;

static int boolval(ppval x)
{
	return x.sign ? big_s_lval(x.u.sv) : big_u_lval(x.u.uv);
}

#if !defined(WCHAR_SIGNEDNESS)
#  if CHAR_MIN == 0
#    define WCHAR_SIGNEDNESS	0
#  else
#    define WCHAR_SIGNEDNESS	1
#  endif
#endif

/*
 * Check the suffix, return 1 if it is signed, 0 otherwise. 1 is
 * returned for a void suffix. Legal suffixes are:
 * unsigned: u U ul uL Ul UL lu Lu lU LU ull uLL Ull ULL llu LLu llU LLU
 * signed: l L ll LL
 */
static int pp_suffix(char *d, char *refc)
{
	if (!*d) return 1;
	if (*d == 'u' || *d == 'U') {
		if (!*(++ d)) return 0;
		if (*d == 'l' || *d == 'L') {
			char *e = d + 1;

			if (*e && *e != *d) goto suffix_error;
			if (!*e || !*(e + 1)) return 0;
			goto suffix_error;
		}
		goto suffix_error;
	}
	if (*d == 'l' || *d == 'L') {
		if (!*(++ d)) return 1;
		if (*d == *(d - 1)) {
			d ++;
			if (!*d) return 1;
		}
		if (*d == 'u' || *d == 'U') {
			d ++;
			if (!*d) return 0;
		}
		goto suffix_error;
	}
suffix_error:
	error(eval_line, "invalid integer constant '%s'", refc);
	throw(eval_exception);
	return 666;
}

static unsigned long pp_char(char *c, char *refc)
{
	unsigned long r = 0;

	c ++;
	if (*c == '\\') {
		int i;

		c ++;
		switch (*c) {
		case 'n': r = '\n'; c ++; break;
		case 't': r = '\t'; c ++; break;
		case 'v': r = '\v'; c ++; break;
		case 'b': r = '\b'; c ++; break;
		case 'r': r = '\r'; c ++; break;
		case 'f': r = '\f'; c ++; break;
		case 'a': r = '\a'; c ++; break;
		case '\\': r = '\\'; c ++; break;
		case '\?': r = '\?'; c ++; break;
		case '\'': r = '\''; c ++; break;
		case '\"': r = '\"'; c ++; break;
		case 'u':
			for (i = 0, c ++; i < 4 && HEXAD(*c); i ++, c ++) {
				r = (r * 16) + HVAL(*c);
			}
			if (i != 4) {
				error(eval_line, "malformed UCN in %s", refc);
				throw(eval_exception);
			}
			break;
		case 'U':
			for (i = 0, c ++; i < 8 && HEXAD(*c); i ++, c ++) {
				r = (r * 16) + HVAL(*c);
			}
			if (i != 8) {
				error(eval_line, "malformed UCN in %s", refc);
				throw(eval_exception);
			}
			break;
		case 'x':
			for (c ++; HEXAD(*c); c ++) r = (r * 16) + HVAL(*c);
			break;
		default:
			if (OCTAL(*c)) {
				r = OVAL(*(c ++));
				if (OCTAL(*c)) r = (r * 8) + OVAL(*(c ++));
				if (OCTAL(*c)) r = (r * 8) + OVAL(*(c ++));
			} else {
				error(eval_line, "invalid escape sequence "
					"'\\%c'", *c);
				throw(eval_exception);
			}
		}
	} else if (*c == '\'') {
		error(eval_line, "empty character constant");
		throw(eval_exception);
	} else {
		r = *((unsigned char *)(c ++));
	}

	if (transient_characters && r < 256) {
		r = transient_characters[(size_t)r];
	}

	if (*c != '\'' && emit_eval_warnings) {
		warning(eval_line, "multicharacter constant");
	}
	return r;
}

static ppval pp_strtoconst(char *refc)
{
	ppval q;
	char *c = refc, *d;
	u_big ru;
	s_big rs;
	int sp, dec;

	if (*c == '\'' || *c == 'L') {
		q.sign = (*c == 'L') ? WCHAR_SIGNEDNESS : 1;
		if (*c == 'L' && *(++ c) != '\'') {
			error(eval_line,
				"invalid wide character constant: %s", refc);
			throw(eval_exception);
		}
		if (q.sign) {
			q.u.sv = big_s_fromlong(pp_char(c, refc));
		} else {
			q.u.uv = big_u_fromulong(pp_char(c, refc));
		}
		return q;
	}
	if (*c == '0') {
		/* octal or hexadecimal */
		dec = 0;
		c ++;
		if (*c == 'x' || *c == 'X') {
			c ++;
			d = big_u_hexconst(c, &ru, &rs, &sp);
		} else {
			d = big_u_octconst(c, &ru, &rs, &sp);
		}
	} else {
		dec = 1;
		d = big_u_decconst(c, &ru, &rs, &sp);
	}
	q.sign = pp_suffix(d, refc);
	if (q.sign) {
		if (!sp) {
			if (dec) {
				error(eval_line, "constant too large "
					"for destination type");
				throw(eval_exception);
			} else {
				warning(eval_line, "constant is so large "
					"that it is unsigned");
			}
			q.u.uv = ru;
			q.sign = 0;
		} else {
			q.u.sv = rs;
		}
	} else {
		q.u.uv = ru;
	}
	return q;
}

/*
 * Used by #line directives -- anything beyond what can be put in an
 * unsigned long, is considered absurd.
 */
unsigned long strtoconst(char *c)
{
	ppval q = pp_strtoconst(c);

	if (q.sign) q.u.uv = big_s_to_u(q.u.sv);
	return big_u_toulong(q.u.uv);
}

#define OP_UN(x)	((x) == LNOT || (x) == NOT || (x) == UPLUS \
			|| (x) == UMINUS)

static ppval eval_opun(int op, ppval v)
{
	if (op == LNOT) {
		v.sign = 1;
		v.u.sv = big_s_fromint(big_s_lnot(v.u.sv));
		return v;
	}
	if (v.sign) {
		switch (op) {
		case NOT: v.u.sv = big_s_not(v.u.sv); break;
		case UPLUS: break;
		case UMINUS: v.u.sv = big_s_neg(v.u.sv); break;
		}
	} else {
		switch (op) {
		case NOT: v.u.uv = big_u_not(v.u.uv); break;
		case UPLUS: break;
		case UMINUS: v.u.uv = big_u_neg(v.u.uv); break;
		}
	}
	return v;
}

#define OP_BIN(x)      ((x) == STAR || (x) == SLASH || (x) == PCT \
                       || (x) == PLUS || (x) == MINUS || (x) == LSH \
                       || (x) == RSH || (x) == LT || (x) == LEQ \
                       || (x) == GT || (x) == GEQ || (x) == SAME \
                       || (x) == NEQ || (x) == AND || (x) == CIRC \
                       || (x) == OR || (x) == LAND || (x) == LOR \
                       || (x) == COMMA)

static ppval eval_opbin(int op, ppval v1, ppval v2)
{
	ppval r;
	int iv2 = 0;

	switch (op) {
	case STAR:	case SLASH:	case PCT:
	case PLUS:	case MINUS:	case AND:
	case CIRC:	case OR:
		/* promote operands, adjust signedness of result */
		if (!v1.sign || !v2.sign) {
			if (v1.sign) {
				v1.u.uv = big_s_to_u(v1.u.sv);
				v1.sign = 0;
			} else if (v2.sign) {
				v2.u.uv = big_s_to_u(v2.u.sv);
				v2.sign = 0;
			}
			r.sign = 0;
		} else {
			r.sign = 1;
		}
		break;
	case LT:	case LEQ:	case GT:
	case GEQ:	case SAME:	case NEQ:
		/* promote operands */
		if (!v1.sign || !v2.sign) {
			if (v1.sign) {
				v1.u.uv = big_s_to_u(v1.u.sv);
				v1.sign = 0;
			} else if (v2.sign) {
				v2.u.uv = big_s_to_u(v2.u.sv);
				v2.sign = 0;
			}
		}
		/* fall through */
	case LAND:
	case LOR:
		/* result is signed anyway */
		r.sign = 1;
		break;
	case LSH:
	case RSH:
		/* result is as signed as left operand; convert right
		   operand to int */
		r.sign = v1.sign;
		if (v2.sign) {
			iv2 = big_s_toint(v2.u.sv);
		} else {
			iv2 = big_u_toint(v2.u.uv);
		}
		break;
	case COMMA:
		if (emit_eval_warnings) {
			warning(eval_line, "ISO C forbids evaluated comma "
				"operators in #if expressions");
		}
		r.sign = v2.sign;
		break;
#ifdef AUDIT
	default: ouch("a good operator is a dead operator");
#endif
	}

#define SBINOP(x)	if (r.sign) r.u.sv = big_s_ ## x (v1.u.sv, v2.u.sv); \
			else r.u.uv = big_u_ ## x (v1.u.uv, v2.u.uv);

#define NSSBINOP(x)	if (v1.sign) r.u.sv = big_s_fromint(big_s_ ## x \
			(v1.u.sv, v2.u.sv)); else r.u.sv = big_s_fromint( \
			big_u_ ## x (v1.u.uv, v2.u.uv));

#define LBINOP(x)	if (v1.sign) r.u.sv = big_s_fromint( \
			big_s_lval(v1.u.sv) x big_s_lval(v2.u.sv)); \
			else r.u.sv = big_s_fromint( \
			big_u_lval(v1.u.uv) x big_u_lval(v2.u.uv));

#define ABINOP(x)	if (r.sign) r.u.sv = big_s_ ## x (v1.u.sv, iv2); \
			else r.u.uv = big_u_ ## x (v1.u.uv, iv2);

	switch (op) {
	case STAR: SBINOP(star); break;
	case SLASH: SBINOP(slash); break;
	case PCT: SBINOP(pct); break;
	case PLUS: SBINOP(plus); break;
	case MINUS: SBINOP(minus); break;
	case LSH: ABINOP(lsh); break;
	case RSH: ABINOP(rsh); break;
	case LT: NSSBINOP(lt); break;
	case LEQ: NSSBINOP(leq); break;
	case GT: NSSBINOP(gt); break;
	case GEQ: NSSBINOP(geq); break;
	case SAME: NSSBINOP(same); break;
	case NEQ: NSSBINOP(neq); break;
	case AND: SBINOP(and); break;
	case CIRC: SBINOP(xor); break;
	case OR: SBINOP(or); break;
	case LAND: LBINOP(&&); break;
	case LOR: LBINOP(||); break;
	case COMMA: r = v2; break;
	}
	return r;
}

#define ttOP(x)		(OP_UN(x) || OP_BIN(x) || (x) == QUEST || (x) == COLON)

static int op_prec(int op)
{
	switch (op) {
	case LNOT:
	case NOT:
	case UPLUS:
	case UMINUS:
		return 13;
	case STAR:
	case SLASH:
	case PCT:
		return 12;
	case PLUS:
	case MINUS:
		return 11;
	case LSH:
	case RSH:
		return 10;
	case LT:
	case LEQ:
	case GT:
	case GEQ:
		return 9;
	case SAME:
	case NEQ:
		return 8;
	case AND:
		return 7;
	case CIRC:
		return 6;
	case OR:
		return 5;
	case LAND:
		return 4;
	case LOR:
		return 3;
	case QUEST:
		return 2;
	case COMMA:
		return 1;
	}
#ifdef AUDIT
	ouch("an unknown species should have a higher precedence");
#endif
	return 666;
}

/*
 * Perform the hard work of evaluation.
 *
 * This function works because:
 * -- all unary operators are right to left associative, and with
 *    identical precedence
 * -- all binary operators are left to right associative
 * -- there is only one non-unary and non-binary operator: the quest-colon
 *
 * If do_eval is 0, the evaluation of operators is not done. This is
 * for sequence point operators (&&, || and ?:).
 */
static ppval eval_shrd(struct token_fifo *tf, int minprec, int do_eval)
{
	ppval top;
	struct token *ct;

	top.sign = 1;
	if (tf->art == tf->nt) goto trunc_err;
	ct = tf->t + (tf->art ++);
	if (ct->type == LPAR) {
		top = eval_shrd(tf, 0, do_eval);
		if (tf->art == tf->nt) goto trunc_err;
		ct = tf->t + (tf->art ++);
		if (ct->type != RPAR) {
			error(eval_line, "a right parenthesis was expected");
			throw(eval_exception);
		}
	} else if (ct->type == NUMBER || ct->type == CHAR) {
		top = pp_strtoconst(ct->name);
	} else if (OP_UN(ct->type)) {
		top = eval_opun(ct->type, eval_shrd(tf,
			op_prec(ct->type), do_eval));
		goto eval_loop;
	} else if (ttOP(ct->type)) goto rogue_op_err;
	else {
		goto invalid_token_err;
	}

eval_loop:
	if (tf->art == tf->nt) {
		return top;
	}
	ct = tf->t + (tf->art ++);
	if (OP_BIN(ct->type)) {
		int bp = op_prec(ct->type);

		if (bp > minprec) {
			ppval tr;

			if ((ct->type == LOR && boolval(top))
				|| (ct->type == LAND && !boolval(top))) {
				tr = eval_shrd(tf, bp, 0);
				if (do_eval) {
					top.sign = 1;
					if (ct->type == LOR)
						top.u.sv = big_s_fromint(1);
					if (ct->type == LAND)
						top.u.sv = big_s_fromint(0);
				}
			} else {
				tr = eval_shrd(tf, bp, do_eval);
				if (do_eval)
					top = eval_opbin(ct->type, top, tr);
			}
			goto eval_loop;
		}
	} else if (ct->type == QUEST) {
		int bp = op_prec(QUEST);
		ppval r1, r2;

		if (bp >= minprec) {
			int qv = boolval(top);

			r1 = eval_shrd(tf, bp, qv ? do_eval : 0);
			if (tf->art == tf->nt) goto trunc_err;
			ct = tf->t + (tf->art ++);
			if (ct->type != COLON) {
				error(eval_line, "a colon was expected");
				throw(eval_exception);
			}
			r2 = eval_shrd(tf, bp, qv ? 0 : do_eval);
			if (do_eval) {
				if (qv) top = r1; else top = r2;
			}
			goto eval_loop;
		}
	}
	tf->art --;
	return top;

trunc_err:
	error(eval_line, "truncated constant integral expression");
	throw(eval_exception);
rogue_op_err:
	error(eval_line, "rogue operator '%s' in constant integral "
		"expression", operators_name[ct->type]);
	throw(eval_exception);
invalid_token_err:
	error(eval_line, "invalid token in constant integral expression");
	throw(eval_exception);
}

#define UNARY(x)	((x) != NUMBER && (x) != NAME && (x) != CHAR \
			&& (x) != RPAR)

/*
 * Evaluate the integer expression contained in the given token_fifo.
 * Evaluation is made by precedence of operators, as described in the
 * Dragon Book. The unary + and - are distinguished from their binary
 * counterparts using the Fortran way: a + or a - is considered unary
 * if it does not follow a constant, an identifier or a right parenthesis.
 */
unsigned long eval_expr(struct token_fifo *tf, int *ret, int ew)
{
	size_t sart;
	ppval r;

	emit_eval_warnings = ew;
	if (catch(eval_exception)) goto eval_err;
	/* first, distinguish unary + and - from binary + and - */
	for (sart = tf->art; tf->art < tf->nt; tf->art ++) {
		if (tf->t[tf->art].type == PLUS) {
			if (sart == tf->art || UNARY(tf->t[tf->art - 1].type))
				tf->t[tf->art].type = UPLUS;
		} else if (tf->t[tf->art].type == MINUS) {
			if (sart == tf->art || UNARY(tf->t[tf->art - 1].type))
				tf->t[tf->art].type = UMINUS;
		}
	}
	tf->art = sart;
	r = eval_shrd(tf, 0, 1);
	if (tf->art < tf->nt) {
		error(eval_line, "trailing garbage in constant integral "
			"expression");
		goto eval_err;
	}
	*ret = 0;
	return boolval(r);
eval_err:
	*ret = 1;
	return 0;
}