// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2002 Roman Zippel <zippel@linux-m68k.org>
 */

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

#include "lkc.h"

#define DEBUG_EXPR      0

static struct expr *expr_eliminate_yn(struct expr *e);

struct expr *expr_alloc_symbol(struct symbol *sym)
{
        struct expr *e = xcalloc(1, 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 = xcalloc(1, 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 = xcalloc(1, 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 = xcalloc(1, 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(const struct expr *org)
{
        struct expr *e;

        if (!org)
                return NULL;

        e = xmalloc(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_GEQ:
        case E_GTH:
        case E_LEQ:
        case E_LTH:
        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:
                fprintf(stderr, "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);
                break;
        case E_EQUAL:
        case E_GEQ:
        case E_GTH:
        case E_LEQ:
        case E_LTH:
        case E_UNEQUAL:
                break;
        case E_OR:
        case E_AND:
                expr_free(e->left.expr);
                expr_free(e->right.expr);
                break;
        default:
                fprintf(stderr, "how to free type %d?\n", e->type);
                break;
        }
        free(e);
}

static int trans_count;

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

/*
 * expr_eliminate_eq() helper.
 *
 * Walks the two expression trees given in 'ep1' and 'ep2'. Any node that does
 * not have type 'type' (E_OR/E_AND) is considered a leaf, and is compared
 * against all other leaves. Two equal leaves are both replaced with either 'y'
 * or 'n' as appropriate for 'type', to be eliminated later.
 */
static void __expr_eliminate_eq(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
        /* Recurse down to leaves */

        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;
        }

        /* e1 and e2 are leaves. Compare them. */

        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;

        /* e1 and e2 are equal leaves. Prepare them for elimination. */

        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:
                ;
        }
}

/*
 * Rewrites the expressions 'ep1' and 'ep2' to remove operands common to both.
 * Example reductions:
 *
 *      ep1: A && B           ->  ep1: y
 *      ep2: A && B && C      ->  ep2: C
 *
 *      ep1: A || B           ->  ep1: n
 *      ep2: A || B || C      ->  ep2: C
 *
 *      ep1: A && (B && FOO)  ->  ep1: FOO
 *      ep2: (BAR && B) && A  ->  ep2: BAR
 *
 *      ep1: A && (B || C)    ->  ep1: y
 *      ep2: (C || B) && A    ->  ep2: y
 *
 * Comparisons are done between all operands at the same "level" of && or ||.
 * For example, in the expression 'e1 && (e2 || e3) && (e4 || e5)', the
 * following operands will be compared:
 *
 *      - 'e1', 'e2 || e3', and 'e4 || e5', against each other
 *      - e2 against e3
 *      - e4 against e5
 *
 * Parentheses are irrelevant within a single level. 'e1 && (e2 && e3)' and
 * '(e1 && e2) && e3' are both a single level.
 *
 * See __expr_eliminate_eq() as well.
 */
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

/*
 * Returns true if 'e1' and 'e2' are equal, after minor simplification. Two
 * &&/|| expressions are considered equal if every operand in one expression
 * equals some operand in the other (operands do not need to appear in the same
 * order), recursively.
 */
int expr_eq(struct expr *e1, struct expr *e2)
{
        int res, old_count;

        /*
         * A NULL expr is taken to be yes, but there's also a different way to
         * represent yes. expr_is_yes() checks for either representation.
         */
        if (!e1 || !e2)
                return expr_is_yes(e1) && expr_is_yes(e2);

        if (e1->type != e2->type)
                return 0;
        switch (e1->type) {
        case E_EQUAL:
        case E_GEQ:
        case E_GTH:
        case E_LEQ:
        case E_LTH:
        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;
}

/*
 * Recursively performs the following simplifications in-place (as well as the
 * corresponding simplifications with swapped operands):
 *
 *      expr && n  ->  n
 *      expr && y  ->  expr
 *      expr || n  ->  expr
 *      expr || y  ->  y
 *
 * Returns the optimized expression.
 */
static 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;
}

/*
 * expr_eliminate_dups() helper.
 *
 * Walks the two expression trees given in 'ep1' and 'ep2'. Any node that does
 * not have type 'type' (E_OR/E_AND) is considered a leaf, and is compared
 * against all other leaves to look for simplifications.
 */
static void expr_eliminate_dups1(enum expr_type type, struct expr **ep1, struct expr **ep2)
{
#define e1 (*ep1)
#define e2 (*ep2)
        struct expr *tmp;

        /* Recurse down to leaves */

        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;
        }

        /* e1 and e2 are leaves. Compare and process them. */

        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
}

/*
 * Rewrites 'e' in-place to remove ("join") duplicate and other redundant
 * operands.
 *
 * Example simplifications:
 *
 *      A || B || A    ->  A || B
 *      A && B && A=y  ->  A=y && B
 *
 * Returns the deduplicated expression.
 */
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);
                default:
                        ;
                }
                if (!trans_count)
                        /* No simplifications done in this pass. We're done */
                        break;
                e = expr_eliminate_yn(e);
        }
        trans_count = oldcount;
        return e;
}

/*
 * Performs various simplifications involving logical operators and
 * comparisons.
 *
 * Allocates and returns a new expression.
 */
struct expr *expr_transform(struct expr *e)
{
        struct expr *tmp;

        if (!e)
                return NULL;
        switch (e->type) {
        case E_EQUAL:
        case E_GEQ:
        case E_GTH:
        case E_LEQ:
        case E_LTH:
        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_LEQ:
                case E_GEQ:
                        // !a<='x' -> a>'x'
                        tmp = e->left.expr;
                        free(e);
                        e = tmp;
                        e->type = e->type == E_LEQ ? E_GTH : E_LTH;
                        break;
                case E_LTH:
                case E_GTH:
                        // !a<'x' -> a>='x'
                        tmp = e->left.expr;
                        free(e);
                        e = tmp;
                        e->type = e->type == E_LTH ? E_GEQ : E_LEQ;
                        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_GEQ:
        case E_GTH:
        case E_LEQ:
        case E_LTH:
        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;
}

/*
 * Inserts explicit comparisons of type 'type' to symbol 'sym' into the
 * expression 'e'.
 *
 * Examples transformations for type == E_UNEQUAL, sym == &symbol_no:
 *
 *      A              ->  A!=n
 *      !A             ->  A=n
 *      A && B         ->  !(A=n || B=n)
 *      A || B         ->  !(A=n && B=n)
 *      A && (B || C)  ->  !(A=n || (B=n && C=n))
 *
 * Allocates and returns a new expression.
 */
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_LTH:
        case E_LEQ:
        case E_GTH:
        case E_GEQ:
        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;
}

enum string_value_kind {
        k_string,
        k_signed,
        k_unsigned,
};

union string_value {
        unsigned long long u;
        signed long long s;
};

static enum string_value_kind expr_parse_string(const char *str,
                                                enum symbol_type type,
                                                union string_value *val)

{
        char *tail;
        enum string_value_kind kind;

        errno = 0;
        switch (type) {
        case S_BOOLEAN:
        case S_TRISTATE:
                val->s = !strcmp(str, "n") ? 0 :
                         !strcmp(str, "m") ? 1 :
                         !strcmp(str, "y") ? 2 : -1;
                return k_signed;
        case S_INT:
                val->s = strtoll(str, &tail, 10);
                kind = k_signed;
                break;
        case S_HEX:
                val->u = strtoull(str, &tail, 16);
                kind = k_unsigned;
                break;
        default:
                val->s = strtoll(str, &tail, 0);
                kind = k_signed;
                break;
        }
        return !errno && !*tail && tail > str && isxdigit(tail[-1])
               ? kind : k_string;
}

tristate expr_calc_value(struct expr *e)
{
        tristate val1, val2;
        const char *str1, *str2;
        enum string_value_kind k1 = k_string, k2 = k_string;
        union string_value lval = {}, rval = {};
        int res;

        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:
        case E_GEQ:
        case E_GTH:
        case E_LEQ:
        case E_LTH:
        case E_UNEQUAL:
                break;
        default:
                printf("expr_calc_value: %d?\n", e->type);
                return no;
        }

        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);

        if (e->left.sym->type != S_STRING || e->right.sym->type != S_STRING) {
                k1 = expr_parse_string(str1, e->left.sym->type, &lval);
                k2 = expr_parse_string(str2, e->right.sym->type, &rval);
        }

        if (k1 == k_string || k2 == k_string)
                res = strcmp(str1, str2);
        else if (k1 == k_unsigned || k2 == k_unsigned)
                res = (lval.u > rval.u) - (lval.u < rval.u);
        else /* if (k1 == k_signed && k2 == k_signed) */
                res = (lval.s > rval.s) - (lval.s < rval.s);

        switch(e->type) {
        case E_EQUAL:
                return res ? no : yes;
        case E_GEQ:
                return res >= 0 ? yes : no;
        case E_GTH:
                return res > 0 ? yes : no;
        case E_LEQ:
                return res <= 0 ? yes : no;
        case E_LTH:
                return res < 0 ? yes : no;
        case E_UNEQUAL:
                return res ? yes : no;
        default:
                printf("expr_calc_value: relation %d?\n", e->type);
                return no;
        }
}

static int expr_compare_type(enum expr_type t1, enum expr_type t2)
{
        if (t1 == t2)
                return 0;
        switch (t1) {
        case E_LEQ:
        case E_LTH:
        case E_GEQ:
        case E_GTH:
                if (t2 == E_EQUAL || t2 == E_UNEQUAL)
                        return 1;
        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;
}

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, "<choice>");
                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_LEQ:
        case E_LTH:
                if (e->left.sym->name)
                        fn(data, e->left.sym, e->left.sym->name);
                else
                        fn(data, NULL, "<choice>");
                fn(data, NULL, e->type == E_LEQ ? "<=" : "<");
                fn(data, e->right.sym, e->right.sym->name);
                break;
        case E_GEQ:
        case E_GTH:
                if (e->left.sym->name)
                        fn(data, e->left.sym, e->left.sym->name);
                else
                        fn(data, NULL, "<choice>");
                fn(data, NULL, e->type == E_GEQ ? ">=" : ">");
                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)
{
        xfwrite(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)
{
        struct gstr *gs = (struct gstr*)data;
        const char *sym_str = NULL;

        if (sym)
                sym_str = sym_get_string_value(sym);

        if (gs->max_width) {
                unsigned extra_length = strlen(str);
                const char *last_cr = strrchr(gs->s, '\n');
                unsigned last_line_length;

                if (sym_str)
                        extra_length += 4 + strlen(sym_str);

                if (!last_cr)
                        last_cr = gs->s;

                last_line_length = strlen(gs->s) - (last_cr - gs->s);

                if ((last_line_length + extra_length) > gs->max_width)
                        str_append(gs, "\\\n");
        }

        str_append(gs, str);
        if (sym && sym->type != S_UNKNOWN)
                str_printf(gs, " [=%s]", sym_str);
}

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

/*
 * Transform the top level "||" tokens into newlines and prepend each
 * line with a minus. This makes expressions much easier to read.
 * Suitable for reverse dependency expressions.
 */
static void expr_print_revdep(struct expr *e,
                              void (*fn)(void *, struct symbol *, const char *),
                              void *data, tristate pr_type, const char **title)
{
        if (e->type == E_OR) {
                expr_print_revdep(e->left.expr, fn, data, pr_type, title);
                expr_print_revdep(e->right.expr, fn, data, pr_type, title);
        } else if (expr_calc_value(e) == pr_type) {
                if (*title) {
                        fn(data, NULL, *title);
                        *title = NULL;
                }

                fn(data, NULL, "  - ");
                expr_print(e, fn, data, E_NONE);
                fn(data, NULL, "\n");
        }
}

void expr_gstr_print_revdep(struct expr *e, struct gstr *gs,
                            tristate pr_type, const char *title)
{
        expr_print_revdep(e, expr_print_gstr_helper, gs, pr_type, &title);
}