path: root/lr0.c

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

#define ARR_LEN(...) (sizeof(__VA_ARGS__) / sizeof(*(__VA_ARGS__)))

enum symbol {
    PLUS = 0,
    MINUS,
    LPAREN,
    RPAREN,
    N0, N1,
    END_INPUT,
    
    EP, E, T, N,
    SYMBOL_COUNT,
};

static inline int is_terminal(enum symbol s)    { return s < E; }
static inline int is_nonterminal(enum symbol s) { return s >= E; }

struct production {
    enum symbol LHS;
    enum symbol *RHS;
    size_t nRHS;
};

#define PROD(LHS, _, ...) {LHS, (enum symbol[]){__VA_ARGS__}, sizeof((enum symbol[]){__VA_ARGS__})/sizeof(enum symbol)}

static struct production grammar[] = {
    PROD(EP, ->, E, END_INPUT),
    PROD(E, -->, E, PLUS, T),
    PROD(E, -->, E, MINUS, T),
    PROD(E, -->, T),
    PROD(T, -->, LPAREN, E, RPAREN),
    PROD(T, -->, N),
    PROD(N, -->, N0),
    PROD(N, -->, N1),
};

void print_grammar()
{
    for(size_t i = 0; i < ARR_LEN(grammar); i++) {
        printf("%d --> ", grammar[i].LHS);
        for(size_t j = 0; j < grammar[i].nRHS; j++)
            printf("%d ", grammar[i].RHS[j]);
        printf("\n");
    }
}

static int follow[SYMBOL_COUNT][SYMBOL_COUNT];
void fill_follow_table();
void print_follow_table()
{
    printf("    ");
    for(size_t i = 0; i < SYMBOL_COUNT; i++) printf("%2zu ", i);
    printf("\n");
    
    for(size_t i = 0; i < SYMBOL_COUNT; i++) {
        printf("%2zu  ", i);
        for(size_t j = 0; j < SYMBOL_COUNT; j++)
            printf(" %s ", follow[i][j] ? "x" : " ");
        printf("\n");
    }    
}

struct action {
    enum action_type {
        ACTION_NOT_SET = 0, ACTION_SHIFT,
        ACTION_GOTO, ACTION_REDUCE,
        ACTION_ACCEPT
    } type;
    size_t arg;
};

// THIS IS BAD, DONT DO IT LIKE THAT
#define TABLE_CAP 64
static struct action table[TABLE_CAP][SYMBOL_COUNT];
// DO IT LIKE THAT
// static struct action *(table[SYMBOL_COUNT]);
static size_t states;

int table_insert(size_t state, enum symbol sym, struct action a);
void print_table()
{
    printf("    ");
    for(size_t sym = 0; sym < SYMBOL_COUNT; sym++) printf("%2zu  ", sym);
    printf("\n");

    char action_to_char[] = {[ACTION_SHIFT] = 's', [ACTION_REDUCE] = 'r', [ACTION_GOTO] = 'g'};
    for(size_t i = 0; i < states; i++) {
        printf("%2zu  ", i);
        for(size_t sym = 0; sym < SYMBOL_COUNT; sym++)
            if(table[i][sym].type == ACTION_ACCEPT) printf(" a  ");
            else if(table[i][sym].type) printf("%c%-2zu ", action_to_char[table[i][sym].type], table[i][sym].arg);
            else printf("    ");
        printf("\n");
    }
}


struct item {
    size_t prod_idx;
    size_t dot;
};

int items_eq(struct item *i1, struct item *i2) { return (i1->dot == i2->dot && i1->prod_idx == i2->prod_idx) ? 1 : 0; }
void print_set(struct item *set, size_t nset)
{
    printf("{");
    for(size_t i = 0; i < nset; i++)
        printf("{%zu, %zu}, ", set[i].prod_idx, set[i].dot);
    printf("}\n");
}

#define SEEN_SETS_CAP 64
static struct {
    struct item *items;
    size_t nitems;
    size_t state;
} seen_sets[SEEN_SETS_CAP];
static size_t nseen_sets;

void free_seen_sets() { for(size_t i = 0; i < nseen_sets; i++) free(seen_sets[i].items);}

size_t handle_set(struct item *set, size_t nset);
int insert_set(size_t state, struct item *initial_set, size_t ninitial);
size_t closure(struct item *in_set, size_t nin, struct item *out_set, size_t nout);

void *xcalloc(size_t n, size_t size) { void *addr = calloc(n, size); return addr ? addr : (exit(1), NULL); }

int main(void)
{
    fill_follow_table();
    
    handle_set((struct item[]){{0, 0}}, 1);
    print_table();
    
    free_seen_sets();
}

size_t handle_set(struct item *set, size_t nset)
{
    // 1. is set in seen_sets
    for(size_t i = 0; i < nseen_sets; i++) {
        if(seen_sets[i].nitems != nset) continue;
        
        int _seen = 0;
        for(size_t j = 0; j < nset; j++) {
            _seen = 0;
            for(size_t k = 0; k < nset; k++)
                if(items_eq(&seen_sets[i].items[k], &set[j])) _seen = 1;
            if(!_seen) break;
        }
        if(_seen) return seen_sets[i].state;
    }

    // 2. add set to seen_sets
    if(nseen_sets >= SEEN_SETS_CAP) {
        fprintf(stderr, "ERROR: SEEN_SET_CAP exceeded\n");
        exit(1);                 
    }
    
    seen_sets[nseen_sets].items = xcalloc(nset, sizeof(*set));
    seen_sets[nseen_sets].nitems = nset;
    for(size_t i = 0; i < nset; i++)
        seen_sets[nseen_sets].items[i] = set[i];

    // 3. insert new state
    size_t new_state = seen_sets[nseen_sets++].state = states++;
    if(new_state >= TABLE_CAP) {
        fprintf(stderr, "ERROR: TABLE_CAP exceeded\n");
        exit(1);
    }

    if(insert_set(new_state, set, nset)) {
        fprintf(stderr, "ERROR: insert_set failed\n");
        exit(1);
    }
    
    return new_state;
}

#define CLOSURE_SET_CAP 64
#define GOTO_SET_CAP 32
int insert_set(size_t state, struct item *initial_set, size_t ninitial)
{
    struct item closure_set[CLOSURE_SET_CAP];
    
    size_t nclosure = closure(initial_set, ninitial, closure_set, CLOSURE_SET_CAP);
    if(nclosure > CLOSURE_SET_CAP) {
        fprintf(stderr, "ERROR: CLOSURE_SET_CAP exceeded\n");
        return 1;
    }
    
    for(size_t sym = 0; sym < SYMBOL_COUNT; sym++) {
        struct item goto_set[GOTO_SET_CAP];
        size_t ngoto = 0; 
        
        for(size_t j = 0; j < nclosure; j++) {
            struct production *p = &grammar[closure_set[j].prod_idx];
            size_t dot = closure_set[j].dot;
            
            if(dot == p->nRHS) {
                if(!follow[p->LHS][sym]) continue;
                if(table_insert(state, sym, (struct action){
                            ACTION_REDUCE, closure_set[j].prod_idx}))
                    return 1;
                continue;
            }
            
            if(p->RHS[dot] == sym) {
                if(ngoto >= GOTO_SET_CAP) {
                    fprintf(stderr, "ERROR: GOTO_SET_CAP exceeded\n");
                    return 1;
                } 
                goto_set[ngoto] = closure_set[j];
                goto_set[ngoto++].dot++;
            }
        }

        if(ngoto == 0) continue;
        
        if(sym == END_INPUT) {
            if(table_insert(state, sym, (struct action){ACTION_ACCEPT, 0}))
                return 1;
            continue;
        }
        
        size_t new_state = handle_set(goto_set, ngoto);

        if(table_insert(state, sym, (struct action){
                    is_terminal(sym) ? ACTION_SHIFT : ACTION_GOTO,
                    new_state})) return 1;
    }
    
    return 0;
}

size_t closure(struct item *in_set, size_t nin, struct item *out_set, size_t nout_max)
{
    size_t nout = nin;
    
    if(nout > nout_max) return nout;
    for(size_t i = 0; i < nin; i++) out_set[i] = in_set[i];

    int *is_in_closure = xcalloc(ARR_LEN(grammar), sizeof(int));
    for(size_t i = 0; i < nout; i++)
    {
        struct production *p = &grammar[out_set[i].prod_idx];
        if(out_set[i].dot == p->nRHS) continue;
        enum symbol sym = p->RHS[out_set[i].dot];
        
        for(size_t j = 0; j < ARR_LEN(grammar); j++)
            if(grammar[j].LHS == sym) {
                if(is_in_closure[j]) continue;
                is_in_closure[j] = 1;

                if(nout++ >= nout_max) goto cleanup;
                out_set[nout-1] = (struct item){j, 0};
            }
    }

cleanup:
    free(is_in_closure);
    return nout;
}

void fill_follow_table()
{
    for(size_t i = 0; i < ARR_LEN(grammar); i++) {
        struct production *p = &grammar[i];
        for(size_t j = 1; j < p->nRHS; j++)
            follow[p->RHS[j-1]][p->RHS[j]] = 1;
    }

#define set(e) if((e) != 1) changed = (e) = 1
    
    int changed;
    do {
        changed = 0;
        for(size_t i = 0; i < ARR_LEN(grammar); i++) 
            for(size_t sym = 0; sym < SYMBOL_COUNT; sym++) {
                struct production *p = &grammar[i];
                if(follow[p->LHS][sym])
                    set(follow[p->RHS[p->nRHS-1]][sym]);
                if(follow[sym][p->LHS])
                    set(follow[sym][p->RHS[0]]);
            }
    } while(changed);
}

int table_insert(size_t state, enum symbol sym, struct action a)
{
    if(table[state][sym].type != ACTION_NOT_SET) {
        fprintf(stderr, "TABLE COLLISION on state '%zu' sym '%d'\n", state, sym);
        fprintf(stderr, "\t{%d %zu} vs {%d %zu}",
                table[state][sym].type, table[state][sym].arg,
                a.type, a.arg);
        return 1;
    }
    
    table[state][sym] = a;
    return 0;
}