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expr.c

/*
 * Copyright (C) 2002 Roman Zippel <zippel@linux-m68k.org>
 * Released under the terms of the GNU GPL v2.0.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define LKC_DIRECT_LINK
#include "lkc.h"

#define DEBUG_EXPR      0

char *choicestring = "<choice>.....\0";

struct expr *expr_alloc_symbol(struct symbol *sym)
{
      struct expr *e = malloc(sizeof(*e));
      memset(e, 0, sizeof(*e));
      e->type = E_SYMBOL;
      e->left.sym = sym;
      return e;
}

struct expr *expr_alloc_one(enum expr_type type, struct expr *ce)
{
      struct expr *e = malloc(sizeof(*e));
      memset(e, 0, sizeof(*e));
      e->type = type;
      e->left.expr = ce;
      return e;
}

struct expr *expr_alloc_two(enum expr_type type, struct expr *e1, struct expr *e2)
{
      struct expr *e = malloc(sizeof(*e));
      memset(e, 0, sizeof(*e));
      e->type = type;
      e->left.expr = e1;
      e->right.expr = e2;
      return e;
}

struct expr *expr_alloc_comp(enum expr_type type, struct symbol *s1, struct symbol *s2)
{
      struct expr *e = malloc(sizeof(*e));
      memset(e, 0, sizeof(*e));
      e->type = type;
      e->left.sym = s1;
      e->right.sym = s2;
      return e;
}

struct expr *expr_alloc_and(struct expr *e1, struct expr *e2)
{
      if (!e1)
            return e2;
      return e2 ? expr_alloc_two(E_AND, e1, e2) : e1;
}

struct expr *expr_alloc_or(struct expr *e1, struct expr *e2)
{
      if (!e1)
            return e2;
      return e2 ? expr_alloc_two(E_OR, e1, e2) : e1;
}

struct expr *expr_copy(struct expr *org)
{
      struct expr *e;

      if (!org)
            return NULL;

      e = malloc(sizeof(*org));
      memcpy(e, org, sizeof(*org));
      switch (org->type) {
      case E_SYMBOL:
            e->left = org->left;
            break;
      case E_NOT:
            e->left.expr = expr_copy(org->left.expr);
            break;
      case E_EQUAL:
      case E_UNEQUAL:
            e->left.sym = org->left.sym;
            e->right.sym = org->right.sym;
            break;
      case E_AND:
      case E_OR:
      case E_LIST:
            e->left.expr = expr_copy(org->left.expr);
            e->right.expr = expr_copy(org->right.expr);
            break;
      default:
            printf("can't copy type %d\n", e->type);
            free(e);
            e = NULL;
            break;
      }

      return e;
}

void expr_free(struct expr *e)
{
      if (!e)
            return;

      switch (e->type) {
      case E_SYMBOL:
            break;
      case E_NOT:
            expr_free(e->left.expr);
            return;
      case E_EQUAL:
      case E_UNEQUAL:
            break;
      case E_OR:
      case E_AND:
            expr_free(e->left.expr);
            expr_free(e->right.expr);
            break;
      default:
            printf("how to free type %d?\n", e->type);
            break;
      }
      free(e);
}

static int trans_count;

#define e1 (*ep1)
#define e2 (*ep2)

static void __expr_eliminate_eq(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
      if (e1->type == type) {
            __expr_eliminate_eq(type, &e1->left.expr, &e2);
            __expr_eliminate_eq(type, &e1->right.expr, &e2);
            return;
      }
      if (e2->type == type) {
            __expr_eliminate_eq(type, &e1, &e2->left.expr);
            __expr_eliminate_eq(type, &e1, &e2->right.expr);
            return;
      }
      if (e1->type == E_SYMBOL && e2->type == E_SYMBOL &&
          e1->left.sym == e2->left.sym &&
          (e1->left.sym == &symbol_yes || e1->left.sym == &symbol_no))
            return;
      if (!expr_eq(e1, e2))
            return;
      trans_count++;
      expr_free(e1); expr_free(e2);
      switch (type) {
      case E_OR:
            e1 = expr_alloc_symbol(&symbol_no);
            e2 = expr_alloc_symbol(&symbol_no);
            break;
      case E_AND:
            e1 = expr_alloc_symbol(&symbol_yes);
            e2 = expr_alloc_symbol(&symbol_yes);
            break;
      default:
            ;
      }
}

void expr_eliminate_eq(struct expr **ep1, struct expr **ep2)
{
      if (!e1 || !e2)
            return;
      switch (e1->type) {
      case E_OR:
      case E_AND:
            __expr_eliminate_eq(e1->type, ep1, ep2);
      default:
            ;
      }
      if (e1->type != e2->type) switch (e2->type) {
      case E_OR:
      case E_AND:
            __expr_eliminate_eq(e2->type, ep1, ep2);
      default:
            ;
      }
      e1 = expr_eliminate_yn(e1);
      e2 = expr_eliminate_yn(e2);
}

#undef e1
#undef e2

int expr_eq(struct expr *e1, struct expr *e2)
{
      int res, old_count;

      if (e1->type != e2->type)
            return 0;
      switch (e1->type) {
      case E_EQUAL:
      case E_UNEQUAL:
            return e1->left.sym == e2->left.sym && e1->right.sym == e2->right.sym;
      case E_SYMBOL:
            return e1->left.sym == e2->left.sym;
      case E_NOT:
            return expr_eq(e1->left.expr, e2->left.expr);
      case E_AND:
      case E_OR:
            e1 = expr_copy(e1);
            e2 = expr_copy(e2);
            old_count = trans_count;
            expr_eliminate_eq(&e1, &e2);
            res = (e1->type == E_SYMBOL && e2->type == E_SYMBOL &&
                   e1->left.sym == e2->left.sym);
            expr_free(e1);
            expr_free(e2);
            trans_count = old_count;
            return res;
      case E_LIST:
      case E_RANGE:
      case E_NONE:
            /* panic */;
      }

      if (DEBUG_EXPR) {
            expr_fprint(e1, stdout);
            printf(" = ");
            expr_fprint(e2, stdout);
            printf(" ?\n");
      }

      return 0;
}

struct expr *expr_eliminate_yn(struct expr *e)
{
      struct expr *tmp;

      if (e) switch (e->type) {
      case E_AND:
            e->left.expr = expr_eliminate_yn(e->left.expr);
            e->right.expr = expr_eliminate_yn(e->right.expr);
            if (e->left.expr->type == E_SYMBOL) {
                  if (e->left.expr->left.sym == &symbol_no) {
                        expr_free(e->left.expr);
                        expr_free(e->right.expr);
                        e->type = E_SYMBOL;
                        e->left.sym = &symbol_no;
                        e->right.expr = NULL;
                        return e;
                  } else if (e->left.expr->left.sym == &symbol_yes) {
                        free(e->left.expr);
                        tmp = e->right.expr;
                        *e = *(e->right.expr);
                        free(tmp);
                        return e;
                  }
            }
            if (e->right.expr->type == E_SYMBOL) {
                  if (e->right.expr->left.sym == &symbol_no) {
                        expr_free(e->left.expr);
                        expr_free(e->right.expr);
                        e->type = E_SYMBOL;
                        e->left.sym = &symbol_no;
                        e->right.expr = NULL;
                        return e;
                  } else if (e->right.expr->left.sym == &symbol_yes) {
                        free(e->right.expr);
                        tmp = e->left.expr;
                        *e = *(e->left.expr);
                        free(tmp);
                        return e;
                  }
            }
            break;
      case E_OR:
            e->left.expr = expr_eliminate_yn(e->left.expr);
            e->right.expr = expr_eliminate_yn(e->right.expr);
            if (e->left.expr->type == E_SYMBOL) {
                  if (e->left.expr->left.sym == &symbol_no) {
                        free(e->left.expr);
                        tmp = e->right.expr;
                        *e = *(e->right.expr);
                        free(tmp);
                        return e;
                  } else if (e->left.expr->left.sym == &symbol_yes) {
                        expr_free(e->left.expr);
                        expr_free(e->right.expr);
                        e->type = E_SYMBOL;
                        e->left.sym = &symbol_yes;
                        e->right.expr = NULL;
                        return e;
                  }
            }
            if (e->right.expr->type == E_SYMBOL) {
                  if (e->right.expr->left.sym == &symbol_no) {
                        free(e->right.expr);
                        tmp = e->left.expr;
                        *e = *(e->left.expr);
                        free(tmp);
                        return e;
                  } else if (e->right.expr->left.sym == &symbol_yes) {
                        expr_free(e->left.expr);
                        expr_free(e->right.expr);
                        e->type = E_SYMBOL;
                        e->left.sym = &symbol_yes;
                        e->right.expr = NULL;
                        return e;
                  }
            }
            break;
      default:
            ;
      }
      return e;
}

/*
 * bool FOO!=n => FOO
 */
struct expr *expr_trans_bool(struct expr *e)
{
      if (!e)
            return NULL;
      switch (e->type) {
      case E_AND:
      case E_OR:
      case E_NOT:
            e->left.expr = expr_trans_bool(e->left.expr);
            e->right.expr = expr_trans_bool(e->right.expr);
            break;
      case E_UNEQUAL:
            // FOO!=n -> FOO
            if (e->left.sym->type == S_TRISTATE) {
                  if (e->right.sym == &symbol_no) {
                        e->type = E_SYMBOL;
                        e->right.sym = NULL;
                  }
            }
            break;
      default:
            ;
      }
      return e;
}

/*
 * e1 || e2 -> ?
 */
static struct expr *expr_join_or(struct expr *e1, struct expr *e2)
{
      struct expr *tmp;
      struct symbol *sym1, *sym2;

      if (expr_eq(e1, e2))
            return expr_copy(e1);
      if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL && e1->type != E_NOT)
            return NULL;
      if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL && e2->type != E_NOT)
            return NULL;
      if (e1->type == E_NOT) {
            tmp = e1->left.expr;
            if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL && tmp->type != E_SYMBOL)
                  return NULL;
            sym1 = tmp->left.sym;
      } else
            sym1 = e1->left.sym;
      if (e2->type == E_NOT) {
            if (e2->left.expr->type != E_SYMBOL)
                  return NULL;
            sym2 = e2->left.expr->left.sym;
      } else
            sym2 = e2->left.sym;
      if (sym1 != sym2)
            return NULL;
      if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
            return NULL;
      if (sym1->type == S_TRISTATE) {
            if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
                ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
                 (e1->right.sym == &symbol_mod && e2->right.sym == &symbol_yes))) {
                  // (a='y') || (a='m') -> (a!='n')
                  return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_no);
            }
            if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
                ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
                 (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes))) {
                  // (a='y') || (a='n') -> (a!='m')
                  return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_mod);
            }
            if (e1->type == E_EQUAL && e2->type == E_EQUAL &&
                ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
                 (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod))) {
                  // (a='m') || (a='n') -> (a!='y')
                  return expr_alloc_comp(E_UNEQUAL, sym1, &symbol_yes);
            }
      }
      if (sym1->type == S_BOOLEAN && sym1 == sym2) {
            if ((e1->type == E_NOT && e1->left.expr->type == E_SYMBOL && e2->type == E_SYMBOL) ||
                (e2->type == E_NOT && e2->left.expr->type == E_SYMBOL && e1->type == E_SYMBOL))
                  return expr_alloc_symbol(&symbol_yes);
      }

      if (DEBUG_EXPR) {
            printf("optimize (");
            expr_fprint(e1, stdout);
            printf(") || (");
            expr_fprint(e2, stdout);
            printf(")?\n");
      }
      return NULL;
}

static struct expr *expr_join_and(struct expr *e1, struct expr *e2)
{
      struct expr *tmp;
      struct symbol *sym1, *sym2;

      if (expr_eq(e1, e2))
            return expr_copy(e1);
      if (e1->type != E_EQUAL && e1->type != E_UNEQUAL && e1->type != E_SYMBOL && e1->type != E_NOT)
            return NULL;
      if (e2->type != E_EQUAL && e2->type != E_UNEQUAL && e2->type != E_SYMBOL && e2->type != E_NOT)
            return NULL;
      if (e1->type == E_NOT) {
            tmp = e1->left.expr;
            if (tmp->type != E_EQUAL && tmp->type != E_UNEQUAL && tmp->type != E_SYMBOL)
                  return NULL;
            sym1 = tmp->left.sym;
      } else
            sym1 = e1->left.sym;
      if (e2->type == E_NOT) {
            if (e2->left.expr->type != E_SYMBOL)
                  return NULL;
            sym2 = e2->left.expr->left.sym;
      } else
            sym2 = e2->left.sym;
      if (sym1 != sym2)
            return NULL;
      if (sym1->type != S_BOOLEAN && sym1->type != S_TRISTATE)
            return NULL;

      if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_yes) ||
          (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_yes))
            // (a) && (a='y') -> (a='y')
            return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

      if ((e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_no) ||
          (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_no))
            // (a) && (a!='n') -> (a)
            return expr_alloc_symbol(sym1);

      if ((e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_mod) ||
          (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_mod))
            // (a) && (a!='m') -> (a='y')
            return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

      if (sym1->type == S_TRISTATE) {
            if (e1->type == E_EQUAL && e2->type == E_UNEQUAL) {
                  // (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
                  sym2 = e1->right.sym;
                  if ((e2->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
                        return sym2 != e2->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
                                               : expr_alloc_symbol(&symbol_no);
            }
            if (e1->type == E_UNEQUAL && e2->type == E_EQUAL) {
                  // (a='b') && (a!='c') -> 'b'='c' ? 'n' : a='b'
                  sym2 = e2->right.sym;
                  if ((e1->right.sym->flags & SYMBOL_CONST) && (sym2->flags & SYMBOL_CONST))
                        return sym2 != e1->right.sym ? expr_alloc_comp(E_EQUAL, sym1, sym2)
                                               : expr_alloc_symbol(&symbol_no);
            }
            if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
                     ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_no) ||
                      (e1->right.sym == &symbol_no && e2->right.sym == &symbol_yes)))
                  // (a!='y') && (a!='n') -> (a='m')
                  return expr_alloc_comp(E_EQUAL, sym1, &symbol_mod);

            if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
                     ((e1->right.sym == &symbol_yes && e2->right.sym == &symbol_mod) ||
                      (e1->right.sym == &symbol_mod && e2->right.sym == &symbol_yes)))
                  // (a!='y') && (a!='m') -> (a='n')
                  return expr_alloc_comp(E_EQUAL, sym1, &symbol_no);

            if (e1->type == E_UNEQUAL && e2->type == E_UNEQUAL &&
                     ((e1->right.sym == &symbol_mod && e2->right.sym == &symbol_no) ||
                      (e1->right.sym == &symbol_no && e2->right.sym == &symbol_mod)))
                  // (a!='m') && (a!='n') -> (a='m')
                  return expr_alloc_comp(E_EQUAL, sym1, &symbol_yes);

            if ((e1->type == E_SYMBOL && e2->type == E_EQUAL && e2->right.sym == &symbol_mod) ||
                (e2->type == E_SYMBOL && e1->type == E_EQUAL && e1->right.sym == &symbol_mod) ||
                (e1->type == E_SYMBOL && e2->type == E_UNEQUAL && e2->right.sym == &symbol_yes) ||
                (e2->type == E_SYMBOL && e1->type == E_UNEQUAL && e1->right.sym == &symbol_yes))
                  return NULL;
      }

      if (DEBUG_EXPR) {
            printf("optimize (");
            expr_fprint(e1, stdout);
            printf(") && (");
            expr_fprint(e2, stdout);
            printf(")?\n");
      }
      return NULL;
}

static void expr_eliminate_dups1(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
#define e1 (*ep1)
#define e2 (*ep2)
      struct expr *tmp;

      if (e1->type == type) {
            expr_eliminate_dups1(type, &e1->left.expr, &e2);
            expr_eliminate_dups1(type, &e1->right.expr, &e2);
            return;
      }
      if (e2->type == type) {
            expr_eliminate_dups1(type, &e1, &e2->left.expr);
            expr_eliminate_dups1(type, &e1, &e2->right.expr);
            return;
      }
      if (e1 == e2)
            return;

      switch (e1->type) {
      case E_OR: case E_AND:
            expr_eliminate_dups1(e1->type, &e1, &e1);
      default:
            ;
      }

      switch (type) {
      case E_OR:
            tmp = expr_join_or(e1, e2);
            if (tmp) {
                  expr_free(e1); expr_free(e2);
                  e1 = expr_alloc_symbol(&symbol_no);
                  e2 = tmp;
                  trans_count++;
            }
            break;
      case E_AND:
            tmp = expr_join_and(e1, e2);
            if (tmp) {
                  expr_free(e1); expr_free(e2);
                  e1 = expr_alloc_symbol(&symbol_yes);
                  e2 = tmp;
                  trans_count++;
            }
            break;
      default:
            ;
      }
#undef e1
#undef e2
}

static void expr_eliminate_dups2(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
#define e1 (*ep1)
#define e2 (*ep2)
      struct expr *tmp, *tmp1, *tmp2;

      if (e1->type == type) {
            expr_eliminate_dups2(type, &e1->left.expr, &e2);
            expr_eliminate_dups2(type, &e1->right.expr, &e2);
            return;
      }
      if (e2->type == type) {
            expr_eliminate_dups2(type, &e1, &e2->left.expr);
            expr_eliminate_dups2(type, &e1, &e2->right.expr);
      }
      if (e1 == e2)
            return;

      switch (e1->type) {
      case E_OR:
            expr_eliminate_dups2(e1->type, &e1, &e1);
            // (FOO || BAR) && (!FOO && !BAR) -> n
            tmp1 = expr_transform(expr_alloc_one(E_NOT, expr_copy(e1)));
            tmp2 = expr_copy(e2);
            tmp = expr_extract_eq_and(&tmp1, &tmp2);
            if (expr_is_yes(tmp1)) {
                  expr_free(e1);
                  e1 = expr_alloc_symbol(&symbol_no);
                  trans_count++;
            }
            expr_free(tmp2);
            expr_free(tmp1);
            expr_free(tmp);
            break;
      case E_AND:
            expr_eliminate_dups2(e1->type, &e1, &e1);
            // (FOO && BAR) || (!FOO || !BAR) -> y
            tmp1 = expr_transform(expr_alloc_one(E_NOT, expr_copy(e1)));
            tmp2 = expr_copy(e2);
            tmp = expr_extract_eq_or(&tmp1, &tmp2);
            if (expr_is_no(tmp1)) {
                  expr_free(e1);
                  e1 = expr_alloc_symbol(&symbol_yes);
                  trans_count++;
            }
            expr_free(tmp2);
            expr_free(tmp1);
            expr_free(tmp);
            break;
      default:
            ;
      }
#undef e1
#undef e2
}

struct expr *expr_eliminate_dups(struct expr *e)
{
      int oldcount;
      if (!e)
            return e;

      oldcount = trans_count;
      while (1) {
            trans_count = 0;
            switch (e->type) {
            case E_OR: case E_AND:
                  expr_eliminate_dups1(e->type, &e, &e);
                  expr_eliminate_dups2(e->type, &e, &e);
            default:
                  ;
            }
            if (!trans_count)
                  break;
            e = expr_eliminate_yn(e);
      }
      trans_count = oldcount;
      return e;
}

struct expr *expr_transform(struct expr *e)
{
      struct expr *tmp;

      if (!e)
            return NULL;
      switch (e->type) {
      case E_EQUAL:
      case E_UNEQUAL:
      case E_SYMBOL:
      case E_LIST:
            break;
      default:
            e->left.expr = expr_transform(e->left.expr);
            e->right.expr = expr_transform(e->right.expr);
      }

      switch (e->type) {
      case E_EQUAL:
            if (e->left.sym->type != S_BOOLEAN)
                  break;
            if (e->right.sym == &symbol_no) {
                  e->type = E_NOT;
                  e->left.expr = expr_alloc_symbol(e->left.sym);
                  e->right.sym = NULL;
                  break;
            }
            if (e->right.sym == &symbol_mod) {
                  printf("boolean symbol %s tested for 'm'? test forced to 'n'\n", e->left.sym->name);
                  e->type = E_SYMBOL;
                  e->left.sym = &symbol_no;
                  e->right.sym = NULL;
                  break;
            }
            if (e->right.sym == &symbol_yes) {
                  e->type = E_SYMBOL;
                  e->right.sym = NULL;
                  break;
            }
            break;
      case E_UNEQUAL:
            if (e->left.sym->type != S_BOOLEAN)
                  break;
            if (e->right.sym == &symbol_no) {
                  e->type = E_SYMBOL;
                  e->right.sym = NULL;
                  break;
            }
            if (e->right.sym == &symbol_mod) {
                  printf("boolean symbol %s tested for 'm'? test forced to 'y'\n", e->left.sym->name);
                  e->type = E_SYMBOL;
                  e->left.sym = &symbol_yes;
                  e->right.sym = NULL;
                  break;
            }
            if (e->right.sym == &symbol_yes) {
                  e->type = E_NOT;
                  e->left.expr = expr_alloc_symbol(e->left.sym);
                  e->right.sym = NULL;
                  break;
            }
            break;
      case E_NOT:
            switch (e->left.expr->type) {
            case E_NOT:
                  // !!a -> a
                  tmp = e->left.expr->left.expr;
                  free(e->left.expr);
                  free(e);
                  e = tmp;
                  e = expr_transform(e);
                  break;
            case E_EQUAL:
            case E_UNEQUAL:
                  // !a='x' -> a!='x'
                  tmp = e->left.expr;
                  free(e);
                  e = tmp;
                  e->type = e->type == E_EQUAL ? E_UNEQUAL : E_EQUAL;
                  break;
            case E_OR:
                  // !(a || b) -> !a && !b
                  tmp = e->left.expr;
                  e->type = E_AND;
                  e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
                  tmp->type = E_NOT;
                  tmp->right.expr = NULL;
                  e = expr_transform(e);
                  break;
            case E_AND:
                  // !(a && b) -> !a || !b
                  tmp = e->left.expr;
                  e->type = E_OR;
                  e->right.expr = expr_alloc_one(E_NOT, tmp->right.expr);
                  tmp->type = E_NOT;
                  tmp->right.expr = NULL;
                  e = expr_transform(e);
                  break;
            case E_SYMBOL:
                  if (e->left.expr->left.sym == &symbol_yes) {
                        // !'y' -> 'n'
                        tmp = e->left.expr;
                        free(e);
                        e = tmp;
                        e->type = E_SYMBOL;
                        e->left.sym = &symbol_no;
                        break;
                  }
                  if (e->left.expr->left.sym == &symbol_mod) {
                        // !'m' -> 'm'
                        tmp = e->left.expr;
                        free(e);
                        e = tmp;
                        e->type = E_SYMBOL;
                        e->left.sym = &symbol_mod;
                        break;
                  }
                  if (e->left.expr->left.sym == &symbol_no) {
                        // !'n' -> 'y'
                        tmp = e->left.expr;
                        free(e);
                        e = tmp;
                        e->type = E_SYMBOL;
                        e->left.sym = &symbol_yes;
                        break;
                  }
                  break;
            default:
                  ;
            }
            break;
      default:
            ;
      }
      return e;
}

int expr_contains_symbol(struct expr *dep, struct symbol *sym)
{
      if (!dep)
            return 0;

      switch (dep->type) {
      case E_AND:
      case E_OR:
            return expr_contains_symbol(dep->left.expr, sym) ||
                   expr_contains_symbol(dep->right.expr, sym);
      case E_SYMBOL:
            return dep->left.sym == sym;
      case E_EQUAL:
      case E_UNEQUAL:
            return dep->left.sym == sym ||
                   dep->right.sym == sym;
      case E_NOT:
            return expr_contains_symbol(dep->left.expr, sym);
      default:
            ;
      }
      return 0;
}

bool expr_depends_symbol(struct expr *dep, struct symbol *sym)
{
      if (!dep)
            return false;

      switch (dep->type) {
      case E_AND:
            return expr_depends_symbol(dep->left.expr, sym) ||
                   expr_depends_symbol(dep->right.expr, sym);
      case E_SYMBOL:
            return dep->left.sym == sym;
      case E_EQUAL:
            if (dep->left.sym == sym) {
                  if (dep->right.sym == &symbol_yes || dep->right.sym == &symbol_mod)
                        return true;
            }
            break;
      case E_UNEQUAL:
            if (dep->left.sym == sym) {
                  if (dep->right.sym == &symbol_no)
                        return true;
            }
            break;
      default:
            ;
      }
      return false;
}

struct expr *expr_extract_eq_and(struct expr **ep1, struct expr **ep2)
{
      struct expr *tmp = NULL;
      expr_extract_eq(E_AND, &tmp, ep1, ep2);
      if (tmp) {
            *ep1 = expr_eliminate_yn(*ep1);
            *ep2 = expr_eliminate_yn(*ep2);
      }
      return tmp;
}

struct expr *expr_extract_eq_or(struct expr **ep1, struct expr **ep2)
{
      struct expr *tmp = NULL;
      expr_extract_eq(E_OR, &tmp, ep1, ep2);
      if (tmp) {
            *ep1 = expr_eliminate_yn(*ep1);
            *ep2 = expr_eliminate_yn(*ep2);
      }
      return tmp;
}

void expr_extract_eq(enum expr_type type, struct expr **ep, struct expr **ep1, struct expr **ep2)
{
#define e1 (*ep1)
#define e2 (*ep2)
      if (e1->type == type) {
            expr_extract_eq(type, ep, &e1->left.expr, &e2);
            expr_extract_eq(type, ep, &e1->right.expr, &e2);
            return;
      }
      if (e2->type == type) {
            expr_extract_eq(type, ep, ep1, &e2->left.expr);
            expr_extract_eq(type, ep, ep1, &e2->right.expr);
            return;
      }
      if (expr_eq(e1, e2)) {
            *ep = *ep ? expr_alloc_two(type, *ep, e1) : e1;
            expr_free(e2);
            if (type == E_AND) {
                  e1 = expr_alloc_symbol(&symbol_yes);
                  e2 = expr_alloc_symbol(&symbol_yes);
            } else if (type == E_OR) {
                  e1 = expr_alloc_symbol(&symbol_no);
                  e2 = expr_alloc_symbol(&symbol_no);
            }
      }
#undef e1
#undef e2
}

struct expr *expr_trans_compare(struct expr *e, enum expr_type type, struct symbol *sym)
{
      struct expr *e1, *e2;

      if (!e) {
            e = expr_alloc_symbol(sym);
            if (type == E_UNEQUAL)
                  e = expr_alloc_one(E_NOT, e);
            return e;
      }
      switch (e->type) {
      case E_AND:
            e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
            e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
            if (sym == &symbol_yes)
                  e = expr_alloc_two(E_AND, e1, e2);
            if (sym == &symbol_no)
                  e = expr_alloc_two(E_OR, e1, e2);
            if (type == E_UNEQUAL)
                  e = expr_alloc_one(E_NOT, e);
            return e;
      case E_OR:
            e1 = expr_trans_compare(e->left.expr, E_EQUAL, sym);
            e2 = expr_trans_compare(e->right.expr, E_EQUAL, sym);
            if (sym == &symbol_yes)
                  e = expr_alloc_two(E_OR, e1, e2);
            if (sym == &symbol_no)
                  e = expr_alloc_two(E_AND, e1, e2);
            if (type == E_UNEQUAL)
                  e = expr_alloc_one(E_NOT, e);
            return e;
      case E_NOT:
            return expr_trans_compare(e->left.expr, type == E_EQUAL ? E_UNEQUAL : E_EQUAL, sym);
      case E_UNEQUAL:
      case E_EQUAL:
            if (type == E_EQUAL) {
                  if (sym == &symbol_yes)
                        return expr_copy(e);
                  if (sym == &symbol_mod)
                        return expr_alloc_symbol(&symbol_no);
                  if (sym == &symbol_no)
                        return expr_alloc_one(E_NOT, expr_copy(e));
            } else {
                  if (sym == &symbol_yes)
                        return expr_alloc_one(E_NOT, expr_copy(e));
                  if (sym == &symbol_mod)
                        return expr_alloc_symbol(&symbol_yes);
                  if (sym == &symbol_no)
                        return expr_copy(e);
            }
            break;
      case E_SYMBOL:
            return expr_alloc_comp(type, e->left.sym, sym);
      case E_LIST:
      case E_RANGE:
      case E_NONE:
            /* panic */;
      }
      return NULL;
}

tristate expr_calc_value(struct expr *e)
{
      tristate val1, val2;
      const char *str1, *str2;

      if (!e)
            return yes;

      switch (e->type) {
      case E_SYMBOL:
            sym_calc_value(e->left.sym);
            return e->left.sym->curr.tri;
      case E_AND:
            val1 = expr_calc_value(e->left.expr);
            val2 = expr_calc_value(e->right.expr);
            return EXPR_AND(val1, val2);
      case E_OR:
            val1 = expr_calc_value(e->left.expr);
            val2 = expr_calc_value(e->right.expr);
            return EXPR_OR(val1, val2);
      case E_NOT:
            val1 = expr_calc_value(e->left.expr);
            return EXPR_NOT(val1);
      case E_EQUAL:
            sym_calc_value(e->left.sym);
            sym_calc_value(e->right.sym);
            str1 = sym_get_string_value(e->left.sym);
            str2 = sym_get_string_value(e->right.sym);
            return !strcmp(str1, str2) ? yes : no;
      case E_UNEQUAL:
            sym_calc_value(e->left.sym);
            sym_calc_value(e->right.sym);
            str1 = sym_get_string_value(e->left.sym);
            str2 = sym_get_string_value(e->right.sym);
            return !strcmp(str1, str2) ? no : yes;
      default:
            printf("expr_calc_value: %d?\n", e->type);
            return no;
      }
}

int expr_compare_type(enum expr_type t1, enum expr_type t2)
{
#if 0
      return 1;
#else
      if (t1 == t2)
            return 0;
      switch (t1) {
      case E_EQUAL:
      case E_UNEQUAL:
            if (t2 == E_NOT)
                  return 1;
      case E_NOT:
            if (t2 == E_AND)
                  return 1;
      case E_AND:
            if (t2 == E_OR)
                  return 1;
      case E_OR:
            if (t2 == E_LIST)
                  return 1;
      case E_LIST:
            if (t2 == 0)
                  return 1;
      default:
            return -1;
      }
      printf("[%dgt%d?]", t1, t2);
      return 0;
#endif
}

void expr_print(struct expr *e, void (*fn)(void *, struct symbol *, const char *), void *data, int prevtoken)
{
      if (!e) {
            fn(data, NULL, "y");
            return;
      }

      if (expr_compare_type(prevtoken, e->type) > 0)
            fn(data, NULL, "(");
      switch (e->type) {
      case E_SYMBOL:
            if (e->left.sym->name)
                  fn(data, e->left.sym, e->left.sym->name);
            else
                  fn(data, NULL, choicestring);
            break;
      case E_NOT:
            fn(data, NULL, "!");
            expr_print(e->left.expr, fn, data, E_NOT);
            break;
      case E_EQUAL:
            if (e->left.sym->name)
                  fn(data, e->left.sym, e->left.sym->name);
            else
                  fn(data, NULL, "<choice>");
            fn(data, NULL, "=");
            fn(data, e->right.sym, e->right.sym->name);
            break;
      case E_UNEQUAL:
            if (e->left.sym->name)
                  fn(data, e->left.sym, e->left.sym->name);
            else
                  fn(data, NULL, "<choice>");
            fn(data, NULL, "!=");
            fn(data, e->right.sym, e->right.sym->name);
            break;
      case E_OR:
            expr_print(e->left.expr, fn, data, E_OR);
            fn(data, NULL, " || ");
            expr_print(e->right.expr, fn, data, E_OR);
            break;
      case E_AND:
            expr_print(e->left.expr, fn, data, E_AND);
            fn(data, NULL, " && ");
            expr_print(e->right.expr, fn, data, E_AND);
            break;
      case E_LIST:
            fn(data, e->right.sym, e->right.sym->name);
            if (e->left.expr) {
                  fn(data, NULL, " ^ ");
                  expr_print(e->left.expr, fn, data, E_LIST);
            }
            break;
      case E_RANGE:
            fn(data, NULL, "[");
            fn(data, e->left.sym, e->left.sym->name);
            fn(data, NULL, " ");
            fn(data, e->right.sym, e->right.sym->name);
            fn(data, NULL, "]");
            break;
      default:
        {
            char buf[32];
            sprintf(buf, "<unknown type %d>", e->type);
            fn(data, NULL, buf);
            break;
        }
      }
      if (expr_compare_type(prevtoken, e->type) > 0)
            fn(data, NULL, ")");
}

static void expr_print_file_helper(void *data, struct symbol *sym, const char *str)
{
      fwrite(str, strlen(str), 1, data);
}

void expr_fprint(struct expr *e, FILE *out)
{
      expr_print(e, expr_print_file_helper, out, E_NONE);
}

static void expr_print_gstr_helper(void *data, struct symbol *sym, const char *str)
{
      str_append((struct gstr*)data, str);
      if (sym)
            str_printf((struct gstr*)data, " [=%s]", sym_get_string_value(sym));
}

void expr_gstr_print(struct expr *e, struct gstr *gs)
{
      expr_print(e, expr_print_gstr_helper, gs, E_NONE);
}

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