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view lwlink/expr.c @ 169:99300be2d3bd
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author | lost |
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date | Sun, 08 Feb 2009 03:00:44 +0000 |
parents | 106c2fe3c9d9 |
children | 299c5d793aca |
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/* expr.c Copyright © 2009 William Astle This file is part of LWLINK. LWLINK is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. */ /* This file contains the actual expression evaluator */ #define __expr_c_seen__ #include <ctype.h> #include <stdlib.h> #include <string.h> #include "expr.h" #include "util.h" lw_expr_stack_t *lw_expr_stack_create(void) { lw_expr_stack_t *s; s = lw_malloc(sizeof(lw_expr_stack_t)); s -> head = NULL; s -> tail = NULL; return s; } void lw_expr_stack_free(lw_expr_stack_t *s) { while (s -> head) { s -> tail = s -> head; s -> head = s -> head -> next; lw_expr_term_free(s -> tail -> term); lw_free(s -> tail); } lw_free(s); } void lw_expr_term_free(lw_expr_term_t *t) { if (t) { if (t -> term_type == LW_TERM_SYM) lw_free(t -> symbol); lw_free(t); } } lw_expr_term_t *lw_expr_term_create_oper(int oper) { lw_expr_term_t *t; t = lw_malloc(sizeof(lw_expr_term_t)); t -> term_type = LW_TERM_OPER; t -> value = oper; return t; } lw_expr_term_t *lw_expr_term_create_int(int val) { lw_expr_term_t *t; t = lw_malloc(sizeof(lw_expr_term_t)); t -> term_type = LW_TERM_INT; t -> value = val; return t; } lw_expr_term_t *lw_expr_term_create_sym(char *sym, int symtype) { lw_expr_term_t *t; t = lw_malloc(sizeof(lw_expr_term_t)); t -> term_type = LW_TERM_SYM; t -> symbol = lw_strdup(sym); t -> value = symtype; return t; } lw_expr_term_t *lw_expr_term_dup(lw_expr_term_t *t) { switch (t -> term_type) { case LW_TERM_INT: return lw_expr_term_create_int(t -> value); case LW_TERM_OPER: return lw_expr_term_create_oper(t -> value); case LW_TERM_SYM: return lw_expr_term_create_sym(t -> symbol, t -> value); default: exit(1); } // can't get here } void lw_expr_stack_push(lw_expr_stack_t *s, lw_expr_term_t *t) { lw_expr_stack_node_t *n; if (!s) { exit(1); } n = lw_malloc(sizeof(lw_expr_stack_node_t)); n -> next = NULL; n -> prev = s -> tail; n -> term = lw_expr_term_dup(t); if (s -> head) { s -> tail -> next = n; s -> tail = n; } else { s -> head = n; s -> tail = n; } } lw_expr_term_t *lw_expr_stack_pop(lw_expr_stack_t *s) { lw_expr_term_t *t; lw_expr_stack_node_t *n; if (!(s -> tail)) return NULL; n = s -> tail; s -> tail = n -> prev; if (!(n -> prev)) { s -> head = NULL; } t = n -> term; n -> term = NULL; lw_free(n); return t; } /* take an expression stack s and scan for operations that can be completed return -1 on error, 0 on no error possible errors are: division by zero or unknown operator theory of operation: scan the stack for an operator which has two constants preceding it (binary) or 1 constant preceding it (unary) and if found, perform the calculation and replace the operator and its operands with the result repeat the scan until no futher simplications are found or if there are no further operators or only a single term remains */ int lw_expr_reval(lw_expr_stack_t *s, lw_expr_stack_t *(*sfunc)(char *sym, int stype, void *state), void *state) { lw_expr_stack_node_t *n, *n2; lw_expr_stack_t *ss; int c; next_iter_sym: // resolve symbols // symbols that do not resolve to an expression are left alone for (c = 0, n = s -> head; n; n = n -> next) { if (n -> term -> term_type == LW_TERM_SYM) { ss = sfunc(n -> term -> symbol, n -> term -> value, state); if (ss) { c++; // splice in the result stack if (n -> prev) { n -> prev -> next = ss -> head; } else { s -> head = ss -> head; } ss -> head -> prev = n -> prev; ss -> tail -> next = n -> next; if (n -> next) { n -> next -> prev = ss -> tail; } else { s -> tail = ss -> tail; } lw_expr_term_free(n -> term); lw_free(n); n = ss -> tail; ss -> head = NULL; ss -> tail = NULL; lw_expr_stack_free(ss); } } } if (c) goto next_iter_sym; next_iter: // a single term if (s -> head == s -> tail) return 0; // search for an operator for (n = s -> head; n; n = n -> next) { if (n -> term -> term_type == LW_TERM_OPER) { if (n -> term -> value == LW_OPER_NEG || n -> term -> value == LW_OPER_COM ) { // unary operator if (n -> prev && n -> prev -> term -> term_type == LW_TERM_INT) { // a unary operator we can resolve // we do the op then remove the term "n" is pointing at if (n -> term -> value == LW_OPER_NEG) { n -> prev -> term -> value = -(n -> prev -> term -> value); } else if (n -> term -> value == LW_OPER_COM) { n -> prev -> term -> value = ~(n -> prev -> term -> value); } n -> prev -> next = n -> next; if (n -> next) n -> next -> prev = n -> prev; else s -> tail = n -> prev; lw_expr_term_free(n -> term); lw_free(n); break; } } else { // binary operator if (n -> prev && n -> prev -> prev && n -> prev -> term -> term_type == LW_TERM_INT && n -> prev -> prev -> term -> term_type == LW_TERM_INT) { // a binary operator we can resolve switch (n -> term -> value) { case LW_OPER_PLUS: n -> prev -> prev -> term -> value += n -> prev -> term -> value; break; case LW_OPER_MINUS: n -> prev -> prev -> term -> value -= n -> prev -> term -> value; break; case LW_OPER_TIMES: n -> prev -> prev -> term -> value *= n -> prev -> term -> value; break; case LW_OPER_DIVIDE: if (n -> prev -> term -> value == 0) return -1; n -> prev -> prev -> term -> value /= n -> prev -> term -> value; break; case LW_OPER_MOD: if (n -> prev -> term -> value == 0) return -1; n -> prev -> prev -> term -> value %= n -> prev -> term -> value; break; case LW_OPER_INTDIV: if (n -> prev -> term -> value == 0) return -1; n -> prev -> prev -> term -> value /= n -> prev -> term -> value; break; case LW_OPER_BWAND: n -> prev -> prev -> term -> value &= n -> prev -> term -> value; break; case LW_OPER_BWOR: n -> prev -> prev -> term -> value |= n -> prev -> term -> value; break; case LW_OPER_BWXOR: n -> prev -> prev -> term -> value ^= n -> prev -> term -> value; break; case LW_OPER_AND: n -> prev -> prev -> term -> value = (n -> prev -> term -> value && n -> prev -> prev -> term -> value) ? 1 : 0; break; case LW_OPER_OR: n -> prev -> prev -> term -> value = (n -> prev -> term -> value || n -> prev -> prev -> term -> value) ? 1 : 0; break; default: // return error if unknown operator! return -1; } // now remove the two unneeded entries from the stack n -> prev -> prev -> next = n -> next; if (n -> next) n -> next -> prev = n -> prev -> prev; else s -> tail = n -> prev -> prev; lw_expr_term_free(n -> term); lw_expr_term_free(n -> prev -> term); lw_free(n -> prev); lw_free(n); break; } } } } // note for the terminally confused about dynamic memory and pointers: // n will not be NULL even after the lw_free calls above so // this test will still work (n will be a dangling pointer) // (n will only be NULL if we didn't find any operators to simplify) if (n) goto next_iter; return 0; }