femtolisp/femtolisp/equal.c

#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <assert.h>
#include <sys/types.h>
#include "llt.h"
#include "flisp.h"

#define BOUNDED_COMPARE_BOUND 2048
#define BOUNDED_HASH_BOUND    4096

// comparable tag
#define cmptag(v) (isfixnum(v) ? TAG_NUM : tag(v))

static value_t eq_class(htable_t *table, value_t key)
{
    value_t c = (value_t)ptrhash_get(table, (void*)key);
    if (c == (value_t)HT_NOTFOUND)
        return NIL;
    if (c == key)
        return c;
    return eq_class(table, c);
}

static void eq_union(htable_t *table, value_t a, value_t b,
                     value_t c, value_t cb)
{
    value_t ca = (c==NIL ? a : c);
    if (cb != NIL)
        ptrhash_put(table, (void*)cb, (void*)ca);
    ptrhash_put(table, (void*)a, (void*)ca);
    ptrhash_put(table, (void*)b, (void*)ca);
}

// a is a fixnum, b is a cprim
static value_t compare_num_cprim(value_t a, value_t b, int eq, int swap)
{
    cprim_t *bcp = (cprim_t*)ptr(b);
    numerictype_t bt = cp_numtype(bcp);
    fixnum_t ia = numval(a);
    void *bptr = cp_data(bcp);
    if (cmp_eq(&ia, T_FIXNUM, bptr, bt, 1))
        return fixnum(0);
    if (eq) return fixnum(1);
    if (swap) {
        if (cmp_lt(bptr, bt, &ia, T_FIXNUM))
            return fixnum(-1);
    }
    else {
        if (cmp_lt(&ia, T_FIXNUM, bptr, bt))
            return fixnum(-1);
    }
    return fixnum(1);
}

static value_t bounded_compare(value_t a, value_t b, int bound, int eq);
static value_t cyc_compare(value_t a, value_t b, htable_t *table, int eq);

static value_t bounded_vector_compare(value_t a, value_t b, int bound, int eq)
{
    size_t la = vector_size(a);
    size_t lb = vector_size(b);
    size_t m, i;
    if (eq && (la!=lb)) return fixnum(1);
    m = la < lb ? la : lb;
    for (i = 0; i < m; i++) {
        value_t d = bounded_compare(vector_elt(a,i), vector_elt(b,i),
                                    bound-1, eq);
        if (d==NIL || numval(d)!=0) return d;
    }
    if (la < lb) return fixnum(-1);
    if (la > lb) return fixnum(1);
    return fixnum(0);
}

// strange comparisons are resolved arbitrarily but consistently.
// ordering: number < cprim < builtin < cvalue < vector < symbol < cons
static value_t bounded_compare(value_t a, value_t b, int bound, int eq)
{
    value_t d;

 compare_top:
    if (a == b) return fixnum(0);
    if (bound <= 0)
        return NIL;
    int taga = tag(a);
    int tagb = cmptag(b);
    switch (taga) {
    case TAG_NUM :
    case TAG_NUM1:
        if (isfixnum(b)) {
            return (numval(a) < numval(b)) ? fixnum(-1) : fixnum(1);
        }
        if (iscprim(b)) {
            return compare_num_cprim(a, b, eq, 0);
        }
        return fixnum(-1);
    case TAG_SYM:
        if (eq) return fixnum(1);
        if (tagb < TAG_SYM) return fixnum(1);
        if (tagb > TAG_SYM) return fixnum(-1);
        return fixnum(strcmp(symbol_name(a), symbol_name(b)));
    case TAG_VECTOR:
        if (isvector(b))
            return bounded_vector_compare(a, b, bound, eq);
        break;
    case TAG_CPRIM:
        if (iscprim(b)) {
            cprim_t *acp=(cprim_t*)ptr(a), *bcp=(cprim_t*)ptr(b);
            numerictype_t at=cp_numtype(acp), bt=cp_numtype(bcp);
            void *aptr=cp_data(acp), *bptr=cp_data(bcp);
            if (cmp_eq(aptr, at, bptr, bt, 1))
                return fixnum(0);
            if (eq) return fixnum(1);
            if (cmp_lt(aptr, at, bptr, bt))
                return fixnum(-1);
            return fixnum(1);
        }
        else if (isfixnum(b)) {
            return compare_num_cprim(b, a, eq, 1);
        }
        break;
    case TAG_CVALUE:
        if (iscvalue(b))
            return cvalue_compare(a, b);
        break;
    case TAG_BUILTIN:
        if (tagb == TAG_BUILTIN) {
            return (uintval(a) < uintval(b)) ? fixnum(-1) : fixnum(1);
        }
        break;
    case TAG_CONS:
        if (tagb < TAG_CONS) return fixnum(1);
        d = bounded_compare(car_(a), car_(b), bound-1, eq);
        if (d==NIL || numval(d) != 0) return d;
        a = cdr_(a); b = cdr_(b);
        bound--;
        goto compare_top;
    }
    return (taga < tagb) ? fixnum(-1) : fixnum(1);
}

static value_t cyc_vector_compare(value_t a, value_t b, htable_t *table,
                                  int eq)
{
    size_t la = vector_size(a);
    size_t lb = vector_size(b);
    size_t m, i;
    value_t d, xa, xb, ca, cb;

    // first try to prove them different with no recursion
    if (eq && (la!=lb)) return fixnum(1);
    m = la < lb ? la : lb;
    for (i = 0; i < m; i++) {
        xa = vector_elt(a,i);
        xb = vector_elt(b,i);
        if (leafp(xa) || leafp(xb)) {
            d = bounded_compare(xa, xb, 1, eq);
            if (numval(d)!=0) return d;
        }
        else if (cmptag(xa) < cmptag(xb)) {
            return fixnum(-1);
        }
        else if (cmptag(xa) > cmptag(xb)) {
            return fixnum(1);
        }
    }

    ca = eq_class(table, a);
    cb = eq_class(table, b);
    if (ca!=NIL && ca==cb)
        return fixnum(0);

    eq_union(table, a, b, ca, cb);

    for (i = 0; i < m; i++) {
        xa = vector_elt(a,i);
        xb = vector_elt(b,i);
        if (!leafp(xa) && !leafp(xb)) {
            d = cyc_compare(xa, xb, table, eq);
            if (numval(d)!=0)
                return d;
        }
    }

    if (la < lb) return fixnum(-1);
    if (la > lb) return fixnum(1);
    return fixnum(0);
}

static value_t cyc_compare(value_t a, value_t b, htable_t *table, int eq)
{
    if (a==b)
        return fixnum(0);
    if (iscons(a)) {
        if (iscons(b)) {
            value_t aa = car_(a); value_t da = cdr_(a);
            value_t ab = car_(b); value_t db = cdr_(b);
            int tagaa = cmptag(aa); int tagda = cmptag(da);
            int tagab = cmptag(ab); int tagdb = cmptag(db);
            value_t d, ca, cb;
            if (leafp(aa) || leafp(ab)) {
                d = bounded_compare(aa, ab, 1, eq);
                if (numval(d)!=0) return d;
            }
            else if (tagaa < tagab)
                return fixnum(-1);
            else if (tagaa > tagab)
                return fixnum(1);
            if (leafp(da) || leafp(db)) {
                d = bounded_compare(da, db, 1, eq);
                if (numval(d)!=0) return d;
            }
            else if (tagda < tagdb)
                return fixnum(-1);
            else if (tagda > tagdb)
                return fixnum(1);

            ca = eq_class(table, a);
            cb = eq_class(table, b);
            if (ca!=NIL && ca==cb)
                return fixnum(0);

            eq_union(table, a, b, ca, cb);
            d = cyc_compare(aa, ab, table, eq);
            if (numval(d)!=0) return d;
            return cyc_compare(da, db, table, eq);
        }
        else {
            return fixnum(1);
        }
    }
    else if (isvector(a) && isvector(b)) {
        return cyc_vector_compare(a, b, table, eq);
    }
    return bounded_compare(a, b, 1, eq);
}

static htable_t equal_eq_hashtable;
void comparehash_init()
{
    htable_new(&equal_eq_hashtable, 512);
}

// 'eq' means unordered comparison is sufficient
static value_t compare_(value_t a, value_t b, int eq)
{
    value_t guess = bounded_compare(a, b, BOUNDED_COMPARE_BOUND, eq);
    if (guess == NIL) {
        guess = cyc_compare(a, b, &equal_eq_hashtable, eq);
        htable_reset(&equal_eq_hashtable, 512);
    }
    return guess;
}

value_t compare(value_t a, value_t b)
{
    return compare_(a, b, 0);
}

value_t equal(value_t a, value_t b)
{
    if (eq_comparable(a, b))
        return (a == b) ? FL_T : FL_F;
    return (numval(compare_(a,b,1))==0 ? FL_T : FL_F);
}

/*
  optimizations:
  - use hash updates instead of calling lookup then insert. i.e. get the
    bp once and use it twice.
  * preallocate hash table and call reset() instead of new/free
  * less redundant tag checking, 3-bit tags
*/

#ifdef BITS64
#define MIX(a, b) int64hash((int64_t)(a) ^ (int64_t)(b));
#define doublehash(a) int64hash(a)
#else
#define MIX(a, b) int64to32hash(((int64_t)(a))<<32 | ((int64_t)(b)))
#define doublehash(a) int64to32hash(a)
#endif

static uptrint_t bounded_hash(value_t a, int bound)
{
    double d;
    numerictype_t nt;
    size_t i, len;
    cvalue_t *cv;
    cprim_t *cp;
    void *data;
    if (bound <= 0) return 0;
    uptrint_t h = 0;
    int bb, tg = tag(a);
    switch(tg) {
    case TAG_NUM :
    case TAG_NUM1:
        d = numval(a);
        return doublehash(*(int64_t*)&d);
    case TAG_BUILTIN:
        return inthash(a);
    case TAG_SYM:
        return ((symbol_t*)ptr(a))->hash;
    case TAG_CPRIM:
        cp = (cprim_t*)ptr(a);
        data = cp_data(cp);
        nt = cp_numtype(cp);
        d = conv_to_double(data, nt);
        if (d==0) d = 0.0;  // normalize -0
        return doublehash(*(int64_t*)&d);
    case TAG_CVALUE:
        cv = (cvalue_t*)ptr(a);
        data = cv_data(cv);
        return memhash(data, cv_len(cv));
    case TAG_VECTOR:
        len = vector_size(a);
        for(i=0; i < len; i++) {
            h = MIX(h, bounded_hash(vector_elt(a,i), bound-1));
        }
        return h;
    case TAG_CONS:
        bb = BOUNDED_HASH_BOUND;
        do {
            h = MIX(h, bounded_hash(car_(a), bound-1)+1);
            bb--;
            if (bb <= 0) return h;
            a = cdr_(a);
        } while (iscons(a));
        return MIX(h, bounded_hash(a, bound-1)+1);
    }
    return 0;
}

int equal_lispvalue(value_t a, value_t b)
{
    if (eq_comparable(a, b))
        return (a==b);
    return (numval(compare_(a,b,1))==0);
}

uptrint_t hash_lispvalue(value_t a)
{
    return bounded_hash(a, BOUNDED_HASH_BOUND);
}

value_t fl_hash(value_t *args, u_int32_t nargs)
{
    argcount("hash", nargs, 1);
    return fixnum(hash_lispvalue(args[0]));
}