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annotate src/expr.c @ 18:218aabbc3b1a
First pass at expression evaluator complete
| author | lost |
|---|---|
| date | Thu, 01 Jan 2009 23:55:18 +0000 |
| parents | df0c4a46af8f |
| children | ec0bf61a5502 |
| rev | line source |
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1 /* |
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2 expr.c |
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3 Copyright © 2008 William Astle |
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4 |
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5 This file is part of LWASM. |
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6 |
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7 LWASM is free software: you can redistribute it and/or modify it under the |
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8 terms of the GNU General Public License as published by the Free Software |
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9 Foundation, either version 3 of the License, or (at your option) any later |
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10 version. |
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11 |
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12 This program is distributed in the hope that it will be useful, but WITHOUT |
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13 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for |
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15 more details. |
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16 |
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17 You should have received a copy of the GNU General Public License along with |
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18 this program. If not, see <http://www.gnu.org/licenses/>. |
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19 */ |
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20 |
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21 /* |
| 18 | 22 This file contains the actual expression evaluator |
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23 */ |
| 14 | 24 |
| 25 #define __expr_c_seen__ | |
| 15 | 26 |
| 18 | 27 #include <ctype.h> |
| 17 | 28 #include <stdio.h> |
| 15 | 29 #include <stdlib.h> |
| 18 | 30 #include <string.h> |
| 15 | 31 |
| 14 | 32 #include "expr.h" |
| 17 | 33 #include "util.h" |
| 34 | |
| 35 lwasm_expr_stack_t *lwasm_expr_stack_create(void) | |
| 36 { | |
| 37 lwasm_expr_stack_t *s; | |
| 38 | |
| 39 s = lwasm_alloc(sizeof(lwasm_expr_stack_t)); | |
| 40 s -> head = NULL; | |
| 41 s -> tail = NULL; | |
| 42 return s; | |
| 43 } | |
| 15 | 44 |
| 17 | 45 void lwasm_expr_stack_free(lwasm_expr_stack_t *s) |
| 46 { | |
| 47 while (s -> head) | |
| 48 { | |
| 49 s -> tail = s -> head; | |
| 50 s -> head = s -> head -> next; | |
| 51 lwasm_expr_term_free(s -> tail -> term); | |
| 52 lwasm_free(s -> tail); | |
| 53 } | |
| 54 lwasm_free(s); | |
| 55 } | |
| 14 | 56 |
| 17 | 57 void lwasm_expr_term_free(lwasm_expr_term_t *t) |
| 58 { | |
| 59 if (t) | |
| 60 { | |
| 61 if (t -> symbol) | |
| 62 lwasm_free(t -> symbol); | |
| 63 lwasm_free(t); | |
| 64 } | |
| 65 } | |
| 66 | |
| 67 lwasm_expr_term_t *lwasm_expr_term_create_oper(int oper) | |
| 68 { | |
| 69 lwasm_expr_term_t *t; | |
| 70 | |
| 71 t = lwasm_alloc(sizeof(lwasm_expr_term_t)); | |
| 72 t -> term_type = LWASM_TERM_OPER; | |
| 73 t -> value = oper; | |
| 74 return t; | |
| 75 } | |
| 15 | 76 |
| 17 | 77 lwasm_expr_term_t *lwasm_expr_term_create_int(int val) |
| 14 | 78 { |
| 17 | 79 lwasm_expr_term_t *t; |
| 80 | |
| 81 t = lwasm_alloc(sizeof(lwasm_expr_term_t)); | |
| 82 t -> term_type = LWASM_TERM_INT; | |
| 83 t -> value = val; | |
| 84 return t; | |
| 85 } | |
| 86 | |
| 87 lwasm_expr_term_t *lwasm_expr_term_create_sym(char *sym) | |
| 88 { | |
| 89 lwasm_expr_term_t *t; | |
| 14 | 90 |
| 17 | 91 t = lwasm_alloc(sizeof(lwasm_expr_term_t)); |
| 92 t -> term_type = LWASM_TERM_SYM; | |
| 93 t -> symbol = lwasm_strdup(sym); | |
| 94 return t; | |
| 95 } | |
| 15 | 96 |
| 17 | 97 lwasm_expr_term_t *lwasm_expr_term_dup(lwasm_expr_term_t *t) |
| 98 { | |
| 99 switch (t -> term_type) | |
| 15 | 100 { |
| 17 | 101 case LWASM_TERM_INT: |
| 102 return lwasm_expr_term_create_int(t -> value); | |
| 103 | |
| 104 case LWASM_TERM_OPER: | |
| 105 return lwasm_expr_term_create_oper(t -> value); | |
| 106 | |
| 107 case LWASM_TERM_SYM: | |
| 108 return lwasm_expr_term_create_sym(t -> symbol); | |
| 109 | |
| 110 default: | |
| 111 fprintf(stderr, "lwasm_expr_term_dup(): invalid term type %d\n", t -> term_type); | |
| 112 exit(1); | |
| 113 } | |
| 114 // can't get here | |
| 115 } | |
| 116 | |
| 117 void lwasm_expr_stack_push(lwasm_expr_stack_t *s, lwasm_expr_term_t *t) | |
| 118 { | |
| 119 lwasm_expr_stack_node_t *n; | |
| 120 | |
| 121 if (!s) | |
| 122 { | |
| 123 fprintf(stderr, "lwasm_expr_stack_push(): invalid stack pointer\n"); | |
| 124 exit(1); | |
| 15 | 125 } |
| 126 | |
| 17 | 127 n = lwasm_alloc(sizeof(lwasm_expr_stack_node_t)); |
| 128 n -> next = NULL; | |
| 129 n -> prev = s -> tail; | |
| 130 n -> term = lwasm_expr_term_dup(t); | |
| 131 | |
| 132 if (s -> head) | |
| 133 { | |
| 134 s -> tail -> next = n; | |
| 135 s -> tail = n; | |
| 136 } | |
| 137 else | |
| 15 | 138 { |
| 17 | 139 s -> head = n; |
| 140 s -> tail = n; | |
| 141 } | |
| 142 } | |
| 143 | |
| 144 lwasm_expr_term_t *lwasm_expr_stack_pop(lwasm_expr_stack_t *s) | |
| 145 { | |
| 146 lwasm_expr_term_t *t; | |
| 147 lwasm_expr_stack_node_t *n; | |
| 148 | |
| 149 if (!(s -> tail)) | |
| 150 return NULL; | |
| 151 | |
| 152 n = s -> tail; | |
| 153 s -> tail = n -> prev; | |
| 154 if (!(n -> prev)) | |
| 155 { | |
| 156 s -> head = NULL; | |
| 15 | 157 } |
| 14 | 158 |
| 17 | 159 t = n -> term; |
| 160 n -> term = NULL; | |
| 161 | |
| 162 lwasm_free(n); | |
| 163 | |
| 164 return t; | |
| 14 | 165 } |
| 18 | 166 |
| 167 // the following two functions are co-routines which actually parse | |
| 168 // an infix expression onto the expression stack, each returns -1 | |
| 169 // if an error is encountered | |
| 170 | |
| 171 /* | |
| 172 parse a term and push it onto the stack | |
| 173 | |
| 174 this function handles unary prefix operators (-, +, .not., .com.) | |
| 175 as well as () | |
| 176 */ | |
| 177 int lwasm_expr_parse_term(lwasm_expr_stack_t *s, const char **p) | |
| 178 { | |
| 179 lwasm_expr_term_t *t; | |
| 180 | |
| 181 eval_next: | |
| 182 if (**p == '(') | |
| 183 { | |
| 184 (*p)++; | |
| 185 lwasm_expr_parse_expr(s, p, 0); | |
| 186 if (**p != ')') | |
| 187 return -1; | |
| 188 (*p)++; | |
| 189 return 0; | |
| 190 } | |
| 191 | |
| 192 if (**p == '+') | |
| 193 { | |
| 194 (*p)++; | |
| 195 goto eval_next; | |
| 196 } | |
| 197 | |
| 198 if (**p == '-') | |
| 199 { | |
| 200 // parse expression following "-" | |
| 201 (*p)++; | |
| 202 if (lwasm_expr_parse_expr(s, p, 200) < 0) | |
| 203 return -1; | |
| 204 t = lwasm_expr_term_create_oper(LWASM_OPER_NEG); | |
| 205 lwasm_expr_stack_push(s, t); | |
| 206 lwasm_expr_term_free(t); | |
| 207 return 0; | |
| 208 } | |
| 209 | |
| 210 /* | |
| 211 we have an actual term here so evaluate it | |
| 212 | |
| 213 it could be one of the following: | |
| 214 | |
| 215 1. a decimal constant | |
| 216 2. a hexadecimal constant | |
| 217 3. an octal constant | |
| 218 4. a binary constant | |
| 219 5. a symbol reference | |
| 220 6. the "current" instruction address (*) | |
| 221 7. the "current" data address (.) | |
| 222 8. a "back reference" (<) | |
| 223 9. a "forward reference" (>) | |
| 224 | |
| 225 items 6 through 9 are stored as symbol references | |
| 226 | |
| 227 (a . followed by a . or a alpha char or number is a symbol) | |
| 228 */ | |
| 229 if (**p == '*' | |
| 230 || ( | |
| 231 **p == '.' | |
| 232 && (*p)[1] != '.' | |
| 233 && !((*p)[1] >= 'A' && (*p)[1] <= 'Z') | |
| 234 && !((*p)[1] >= 'a' && (*p)[1] <= 'z') | |
| 235 && !((*p)[1] >= '0' && (*p)[1] <= '9') | |
| 236 ) | |
| 237 || **p == '<' | |
| 238 || **p == '>') | |
| 239 { | |
| 240 char tstr[2]; | |
| 241 tstr[0] = **p; | |
| 242 tstr[1] = '\0'; | |
| 243 t = lwasm_expr_term_create_sym(tstr); | |
| 244 lwasm_expr_stack_push(s, t); | |
| 245 lwasm_expr_term_free(t); | |
| 246 (*p)++; | |
| 247 return 0; | |
| 248 } | |
| 249 | |
| 250 /* | |
| 251 - a symbol will be a string of characters introduced by a letter, ".", | |
| 252 "_" but NOT a number | |
| 253 - a decimal constant will consist of only digits, optionally prefixed | |
| 254 with "&" | |
| 255 - a binary constant will consist of only 0s and 1s either prefixed with % | |
| 256 or suffixed with "B" | |
| 257 - a hex constant will consist of 0-9A-F either prefixed with $ or | |
| 258 suffixed with "H"; a hex number starting with A-F must be prefixed | |
| 259 with $ or start with 0 and end with H | |
| 260 - an octal constant will consist of 0-7 either prefixed with @ or | |
| 261 suffixed with "O" or "Q" | |
| 262 - an ascii constant will be a single character prefixed with a ' | |
| 263 - a double ascii constant will be two characters prefixed with a " | |
| 264 | |
| 265 */ | |
| 266 if (**p == '"') | |
| 267 { | |
| 268 // double ascii constant | |
| 269 int val; | |
| 270 (*p)++; | |
| 271 if (!**p) | |
| 272 return -1; | |
| 273 if (!*((*p)+1)) | |
| 274 return -1; | |
| 275 val = **p << 8 | *((*p) + 1); | |
| 276 (*p) += 2; | |
| 277 t = lwasm_expr_term_create_int(val); | |
| 278 lwasm_expr_stack_push(s, t); | |
| 279 lwasm_expr_term_free(t); | |
| 280 return 0; | |
| 281 } | |
| 282 else if (**p == '\'') | |
| 283 { | |
| 284 // single ascii constant | |
| 285 int val; | |
| 286 (*p)++; | |
| 287 if (!**p) | |
| 288 return -1; | |
| 289 val = **p; | |
| 290 (*p)++; | |
| 291 t = lwasm_expr_term_create_int(val); | |
| 292 lwasm_expr_stack_push(s, t); | |
| 293 lwasm_expr_term_free(t); | |
| 294 } | |
| 295 else if (**p == '&') | |
| 296 { | |
| 297 // decimal constant | |
| 298 int val = 0; | |
| 299 | |
| 300 (*p)++; | |
| 301 while (strchr("0123456789", **p)) | |
| 302 { | |
| 303 val = val * 10 + (**p - '0'); | |
| 304 (*p)++; | |
| 305 } | |
| 306 t = lwasm_expr_term_create_int(val); | |
| 307 lwasm_expr_stack_push(s, t); | |
| 308 lwasm_expr_term_free(t); | |
| 309 return 0; | |
| 310 } | |
| 311 else if (**p == '%') | |
| 312 { | |
| 313 // binary constant | |
| 314 int val = 0; | |
| 315 | |
| 316 (*p)++; | |
| 317 while (**p == '0' || **p == '1') | |
| 318 { | |
| 319 val = val * 2 + (**p - '0'); | |
| 320 (*p)++; | |
| 321 } | |
| 322 t = lwasm_expr_term_create_int(val); | |
| 323 lwasm_expr_stack_push(s, t); | |
| 324 lwasm_expr_term_free(t); | |
| 325 return 0; | |
| 326 } | |
| 327 else if (**p == '$') | |
| 328 { | |
| 329 // hexadecimal constant | |
| 330 int val = 0, val2; | |
| 331 | |
| 332 (*p)++; | |
| 333 while (strchr("0123456789ABCDEFabcdef", **p)) | |
| 334 { | |
| 335 val2 = toupper(**p) - '0'; | |
| 336 if (val2 > 9) | |
| 337 val2 -= 7; | |
| 338 val = val * 16 + val2; | |
| 339 (*p)++; | |
| 340 } | |
| 341 t = lwasm_expr_term_create_int(val); | |
| 342 lwasm_expr_stack_push(s, t); | |
| 343 lwasm_expr_term_free(t); | |
| 344 return 0; | |
| 345 } | |
| 346 else if (**p == '@') | |
| 347 { | |
| 348 // octal constant | |
| 349 int val = 0; | |
| 350 | |
| 351 (*p)++; | |
| 352 while (strchr("01234567", **p)) | |
| 353 { | |
| 354 val = val * 8 + (**p - '0'); | |
| 355 (*p)++; | |
| 356 } | |
| 357 t = lwasm_expr_term_create_int(val); | |
| 358 lwasm_expr_stack_push(s, t); | |
| 359 lwasm_expr_term_free(t); | |
| 360 return 0; | |
| 361 } | |
| 362 | |
| 363 // symbol or bare decimal or suffix identified constant here | |
| 364 // all numbers will start with a digit at this point | |
| 365 if (**p < '0' || **p > '9') | |
| 366 { | |
| 367 int l = 0; | |
| 368 char *sb; | |
| 369 | |
| 370 // evaluate a symbol here | |
| 371 static const char *symchars = "_.$@\\abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; | |
| 372 while (strchr(symchars, (*p)[l])) | |
| 373 l++; | |
| 374 | |
| 375 if (l == 0) | |
| 376 return -1; | |
| 377 | |
| 378 sb = lwasm_alloc(l + 1); | |
| 379 sb[l] = '\0'; | |
| 380 memcpy(sb, *p, l); | |
| 381 t = lwasm_expr_term_create_sym(sb); | |
| 382 lwasm_expr_stack_push(s, t); | |
| 383 lwasm_expr_term_free(t); | |
| 384 lwasm_free(sb); | |
| 385 (*p) += l; | |
| 386 return 0; | |
| 387 } | |
| 388 | |
| 389 if (!**p) | |
| 390 return -1; | |
| 391 | |
| 392 // evaluate a suffix based constant | |
| 393 { | |
| 394 int decval = 0, binval = 0, hexval = 0, octval = 0; | |
| 395 int valtype = 15; // 1 = bin, 2 = oct, 4 = dec, 8 = hex | |
| 396 int bindone = 0; | |
| 397 int val; | |
| 398 int dval; | |
| 399 | |
| 400 while (1) | |
| 401 { | |
| 402 if (!**p || !strchr("0123456789ABCDEFabcdefqhoQHO", **p)) | |
| 403 { | |
| 404 // we can legally have bin or decimal here | |
| 405 if (bindone) | |
| 406 { | |
| 407 // we just finished a binary value | |
| 408 val = binval; | |
| 409 break; | |
| 410 } | |
| 411 else if (valtype & 4) | |
| 412 { | |
| 413 // otherwise we must be decimal (if we're still allowed one) | |
| 414 val = decval; | |
| 415 break; | |
| 416 } | |
| 417 else | |
| 418 { | |
| 419 // bad value | |
| 420 return -1; | |
| 421 } | |
| 422 } | |
| 423 | |
| 424 dval = toupper(**p); | |
| 425 (*p)++; | |
| 426 | |
| 427 if (bindone) | |
| 428 { | |
| 429 // any characters past "B" means it is not binary | |
| 430 bindone = 0; | |
| 431 valtype &= 14; | |
| 432 } | |
| 433 | |
| 434 switch (dval) | |
| 435 { | |
| 436 case 'Q': | |
| 437 case 'O': | |
| 438 if (valtype & 2) | |
| 439 { | |
| 440 val = octval; | |
| 441 valtype = -1; | |
| 442 break; | |
| 443 } | |
| 444 else | |
| 445 { | |
| 446 // not a valid octal value | |
| 447 return -1; | |
| 448 } | |
| 449 /* can't get here */ | |
| 450 | |
| 451 case 'H': | |
| 452 if (valtype & 8) | |
| 453 { | |
| 454 val = hexval; | |
| 455 valtype = -1; | |
| 456 break; | |
| 457 } | |
| 458 else | |
| 459 { | |
| 460 // not a valid hex number | |
| 461 return -1; | |
| 462 } | |
| 463 /* can't get here */ | |
| 464 | |
| 465 case 'B': | |
| 466 // this is a bit of a sticky one since B is a legit hex | |
| 467 // digit so this may or may not be the end of the number | |
| 468 // so we fall through to the digit case | |
| 469 | |
| 470 if (valtype & 1) | |
| 471 { | |
| 472 // could still be binary | |
| 473 bindone = 1; | |
| 474 valtype = 9; // hex and binary | |
| 475 } | |
| 476 /* fall through intentional */ | |
| 477 | |
| 478 default: | |
| 479 // digit | |
| 480 dval -= '0'; | |
| 481 if (dval > 9) | |
| 482 dval -= 7; | |
| 483 | |
| 484 if (valtype & 8) | |
| 485 { | |
| 486 hexval = hexval * 16 + dval; | |
| 487 } | |
| 488 if (valtype & 4) | |
| 489 { | |
| 490 if (dval > 9) | |
| 491 valtype &= 11; | |
| 492 else | |
| 493 decval = decval * 10 + dval; | |
| 494 } | |
| 495 if (valtype & 2) | |
| 496 { | |
| 497 if (dval > 7) | |
| 498 valtype &= 13; | |
| 499 else | |
| 500 octval = octval * 8 + dval; | |
| 501 } | |
| 502 if (valtype & 1) | |
| 503 { | |
| 504 if (dval > 1) | |
| 505 valtype &= 14; | |
| 506 else | |
| 507 binval = binval * 2 + dval; | |
| 508 } | |
| 509 } | |
| 510 // break out if we have a return value | |
| 511 if (valtype = -1) | |
| 512 break; | |
| 513 // return if no more valid possibilities! | |
| 514 if (valtype == 0) | |
| 515 return -1; | |
| 516 } | |
| 517 | |
| 518 // we get here when we have a value to return | |
| 519 t = lwasm_expr_term_create_int(val); | |
| 520 lwasm_expr_stack_push(s, t); | |
| 521 lwasm_expr_term_free(t); | |
| 522 return 0; | |
| 523 } | |
| 524 /* can't get here */ | |
| 525 } | |
| 526 | |
| 527 // parse an expression and push the result onto the stack | |
| 528 // if an operator of lower precedence than the value of "prec" is found, | |
| 529 int lwasm_expr_parse_expr(lwasm_expr_stack_t *s, const char **p, int prec) | |
| 530 { | |
| 531 static const struct operinfo | |
| 532 { | |
| 533 int opernum; | |
| 534 char *operstr; | |
| 535 int operprec; | |
| 536 } operators[] = | |
| 537 { | |
| 538 { LWASM_OPER_PLUS, "+", 100 }, | |
| 539 { LWASM_OPER_MINUS, "-", 100 }, | |
| 540 { LWASM_OPER_TIMES, "*", 150 }, | |
| 541 { LWASM_OPER_DIVIDE, "/", 150 }, | |
| 542 { LWASM_OPER_MOD, "%", 150 }, | |
| 543 { LWASM_OPER_INTDIV, "\\", 150 }, | |
| 544 | |
| 545 { LWASM_OPER_NONE, "", 0 } | |
| 546 }; | |
| 547 int opern, i; | |
| 548 lwasm_expr_term_t *operterm; | |
| 549 | |
| 550 // return if we are at the end of the expression or a subexpression | |
| 551 if (!**p || isspace(**p) || **p == ')') | |
| 552 return 0; | |
| 553 | |
| 554 eval_next: | |
| 555 if (lwasm_expr_parse_term(s, p) < 0) | |
| 556 return -1; | |
| 557 | |
| 558 // expecting an operator here | |
| 559 for (opern = 0; operators[opern].opernum != LWASM_OPER_NONE; opern++) | |
| 560 { | |
| 561 for (i = 0; (*p)[i] && operators[opern].operstr[i] && (*p[i] == operators[opern].operstr[i]); i++) | |
| 562 /* do nothing */ ; | |
| 563 if (operators[opern].operstr[i] == '\0') | |
| 564 break; | |
| 565 } | |
| 566 if (operators[opern].opernum == LWASM_OPER_NONE) | |
| 567 { | |
| 568 // unrecognized operator | |
| 569 return -1; | |
| 570 } | |
| 571 | |
| 572 // the operator number in question is in opern; i is the length of the | |
| 573 // operator string | |
| 574 | |
| 575 // logic: | |
| 576 // if the precedence of this operation is <= to the "prec" flag, | |
| 577 // we simply return without advancing the input pointer; the operator | |
| 578 // will be evaluated again in the enclosing function call | |
| 579 if (operators[opern].operprec <= prec) | |
| 580 return 0; | |
| 581 | |
| 582 // logic: | |
| 583 // we have a higher precedence operator here so we will advance the | |
| 584 // input pointer to the next term and let the expression evaluator | |
| 585 // loose on it after which time we will push our operator onto the | |
| 586 // stack and then go on with the expression evaluation | |
| 587 (*p) += i; // advance input pointer | |
| 588 | |
| 589 // evaluate next expression(s) of higher precedence | |
| 590 if (lwasm_expr_parse_expr(s, p, operators[opern].operprec) < 0) | |
| 591 return -1; | |
| 592 | |
| 593 operterm = lwasm_expr_term_create_oper(operators[opern].opernum); | |
| 594 lwasm_expr_stack_push(s, operterm); | |
| 595 lwasm_expr_term_free(operterm); | |
| 596 | |
| 597 // return if we are at the end of the expression or a subexpression | |
| 598 if (!**p || isspace(**p) || **p == ')') | |
| 599 return 0; | |
| 600 | |
| 601 // continue evaluating | |
| 602 goto eval_next; | |
| 603 } | |
| 604 | |
| 605 /* | |
| 606 actually evaluate an expression | |
| 607 | |
| 608 This happens in two stages. The first stage merely parses the expression into | |
| 609 a lwasm_expr_stack_t * which is then evaluated as much as possible before the | |
| 610 result is returned. | |
| 611 | |
| 612 Returns NULL on a parse error or otherwise invalid expression. *outp will | |
| 613 contain the pointer to the next character after the expression if and only | |
| 614 if there is no error. In the case of an error, *outp is undefined. | |
| 615 */ | |
| 616 lwasm_expr_stack_t *lwasm_expr_eval(const char *inp, const char **outp) | |
| 617 { | |
| 618 lwasm_expr_stack_t *s; | |
| 619 const char *p; | |
| 620 | |
| 621 // actually parse the expression | |
| 622 p = inp; | |
| 623 s = lwasm_expr_stack_create(); | |
| 624 if (lwasm_expr_parse_expr(s, &p, 0) < 0) | |
| 625 goto cleanup_error; | |
| 626 | |
| 627 // save end of expression | |
| 628 if (outp) | |
| 629 (*outp) = p; | |
| 630 | |
| 631 // return potentially partial expression | |
| 632 if (lwasm_expr_reval(s) < 0) | |
| 633 goto cleanup_error; | |
| 634 | |
| 635 return s; | |
| 636 | |
| 637 cleanup_error: | |
| 638 lwasm_expr_stack_free(s); | |
| 639 return NULL; | |
| 640 } | |
| 641 | |
| 642 /* | |
| 643 take an expression stack s and scan for operations that can be completed | |
| 644 | |
| 645 return -1 on error, 0 on no error | |
| 646 | |
| 647 possible errors are: division by zero or unknown operator | |
| 648 | |
| 649 theory of operation: | |
| 650 | |
| 651 scan the stack for an operator which has two constants preceding it (binary) | |
| 652 or 1 constant preceding it (unary) and if found, perform the calculation | |
| 653 and replace the operator and its operands with the result | |
| 654 | |
| 655 repeat the scan until no futher simplications are found or if there are no | |
| 656 further operators or only a single term remains | |
| 657 | |
| 658 */ | |
| 659 int lwasm_expr_reval(lwasm_expr_stack_t *s) | |
| 660 { | |
| 661 lwasm_expr_stack_node_t *n; | |
| 662 | |
| 663 next_iter: | |
| 664 // a single term | |
| 665 if (s -> head == s -> tail) | |
| 666 return 0; | |
| 667 | |
| 668 // search for an operator | |
| 669 for (n = s -> head; n; n = n -> next) | |
| 670 { | |
| 671 if (n -> term -> term_type == LWASM_TERM_OPER) | |
| 672 { | |
| 673 if (n -> term -> value == LWASM_OPER_NEG | |
| 674 || n -> term -> value == LWASM_OPER_COM | |
| 675 ) | |
| 676 { | |
| 677 // unary operator | |
| 678 if (n -> prev && n -> prev -> term -> term_type == LWASM_TERM_INT) | |
| 679 { | |
| 680 // a unary operator we can resolve | |
| 681 // we do the op then remove the term "n" is pointing at | |
| 682 if (n -> term -> value == LWASM_OPER_NEG) | |
| 683 { | |
| 684 n -> prev -> term -> value = -(n -> prev -> term -> value); | |
| 685 } | |
| 686 else if (n -> term -> value == LWASM_OPER_COM) | |
| 687 { | |
| 688 n -> prev -> term -> value = ~(n -> prev -> term -> value); | |
| 689 } | |
| 690 n -> prev -> next = n -> next; | |
| 691 if (n -> next) | |
| 692 n -> next -> prev = n -> prev; | |
| 693 else | |
| 694 s -> tail = n -> prev; | |
| 695 | |
| 696 lwasm_expr_term_free(n -> term); | |
| 697 lwasm_free(n); | |
| 698 break; | |
| 699 } | |
| 700 } | |
| 701 else | |
| 702 { | |
| 703 // binary operator | |
| 704 if (n -> prev && n -> prev -> prev && n -> prev -> term -> term_type == LWASM_TERM_INT && n -> prev -> prev -> term -> term_type == LWASM_TERM_INT) | |
| 705 { | |
| 706 // a binary operator we can resolve | |
| 707 switch (n -> term -> value) | |
| 708 { | |
| 709 case LWASM_OPER_PLUS: | |
| 710 n -> prev -> prev -> term -> value += n -> prev -> term -> value; | |
| 711 break; | |
| 712 | |
| 713 case LWASM_OPER_MINUS: | |
| 714 n -> prev -> prev -> term -> value -= n -> prev -> term -> value; | |
| 715 break; | |
| 716 | |
| 717 case LWASM_OPER_TIMES: | |
| 718 n -> prev -> prev -> term -> value *= n -> prev -> term -> value; | |
| 719 break; | |
| 720 | |
| 721 case LWASM_OPER_DIVIDE: | |
| 722 if (n -> prev -> term -> value == 0) | |
| 723 return -1; | |
| 724 n -> prev -> prev -> term -> value /= n -> prev -> term -> value; | |
| 725 break; | |
| 726 | |
| 727 case LWASM_OPER_MOD: | |
| 728 if (n -> prev -> term -> value == 0) | |
| 729 return -1; | |
| 730 n -> prev -> prev -> term -> value %= n -> prev -> term -> value; | |
| 731 break; | |
| 732 | |
| 733 case LWASM_OPER_INTDIV: | |
| 734 if (n -> prev -> term -> value == 0) | |
| 735 return -1; | |
| 736 n -> prev -> prev -> term -> value /= n -> prev -> term -> value; | |
| 737 break; | |
| 738 | |
| 739 case LWASM_OPER_BWAND: | |
| 740 n -> prev -> prev -> term -> value &= n -> prev -> term -> value; | |
| 741 break; | |
| 742 | |
| 743 case LWASM_OPER_BWOR: | |
| 744 n -> prev -> prev -> term -> value |= n -> prev -> term -> value; | |
| 745 break; | |
| 746 | |
| 747 case LWASM_OPER_BWXOR: | |
| 748 n -> prev -> prev -> term -> value ^= n -> prev -> term -> value; | |
| 749 break; | |
| 750 | |
| 751 case LWASM_OPER_AND: | |
| 752 n -> prev -> prev -> term -> value = (n -> prev -> term -> value && n -> prev -> prev -> term -> value) ? 1 : 0; | |
| 753 break; | |
| 754 | |
| 755 case LWASM_OPER_OR: | |
| 756 n -> prev -> prev -> term -> value = (n -> prev -> term -> value || n -> prev -> prev -> term -> value) ? 1 : 0; | |
| 757 break; | |
| 758 | |
| 759 default: | |
| 760 // return error if unknown operator! | |
| 761 return -1; | |
| 762 } | |
| 763 | |
| 764 // now remove the two unneeded entries from the stack | |
| 765 n -> prev -> prev -> next = n -> next; | |
| 766 if (n -> next) | |
| 767 n -> next -> prev = n -> prev -> prev; | |
| 768 else | |
| 769 s -> tail = n -> prev -> prev; | |
| 770 | |
| 771 lwasm_expr_term_free(n -> term); | |
| 772 lwasm_expr_term_free(n -> prev -> term); | |
| 773 lwasm_free(n -> prev); | |
| 774 lwasm_free(n); | |
| 775 break; | |
| 776 } | |
| 777 } | |
| 778 } | |
| 779 } | |
| 780 // note for the terminally confused about dynamic memory and pointers: | |
| 781 // n will not be NULL even after the lwasm_free calls above so | |
| 782 // this test will still work (n will be a dangling pointer) | |
| 783 // (n will only be NULL if we didn't find any operators to simplify) | |
| 784 if (n) | |
| 785 goto next_iter; | |
| 786 | |
| 787 return 0; | |
| 788 } |