treetrie-2015/critbit.c

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stdint.h>
#include <errno.h>
#include <assert.h>

#include "treetrie.h"
#include "critbit.h"

/* We abuse the representation of leaves (being a pair of a GC'd
   pointer and a non-GC'd integer) as the representation of our dict
   trees, too, since we need a place to store the size of the dict. */
#define TT_TAG_DICT TT_TAG_LEAF
#define TT_DICT_ROOT(a,p) TT_LEAF_TRIE(a,p)
#define TT_DICT_SIZE(a,p) TT_LEAF_ATOM(a,p)
#define tt_cons_dict(a,root,size) tt_cons_leaf(a,root,size)

#define RET_IF_NO_PTR(v) \
  ({ tt_node_ptr_t ___w = (v); if (___w == TT_NO_PTR) return TT_NO_PTR; ___w; })

int tt_dict_size(tt_arena_t *a, tt_node_ptr_t t) {
  if (t == TT_EMPTY) {
    return 0;
  } else {
    assert(tt_ptr_tag(t) == TT_TAG_DICT);
    return TT_DICT_SIZE(a,t);
  }
}

static inline int bit_ref(tt_atom_t key, unsigned int bit) {
  return key & (1 << bit);
}

tt_node_ptr_t tt_dict_get(tt_arena_t *a, tt_node_ptr_t t, tt_atom_t key) {
  if (t == TT_EMPTY) {
    return TT_NO_PTR;
  }

  assert(tt_ptr_tag(t) == TT_TAG_DICT);
  t = TT_DICT_ROOT(a,t);

  while (tt_ptr_tag(t) == TT_TAG_NODE) {
    t = bit_ref(key, TT_NODE_INDEX(a, t)) ? TT_NODE_ONE(a, t) : TT_NODE_ZERO(a, t);
  }

  assert(tt_ptr_tag(t) == TT_TAG_LEAF);
  return (TT_LEAF_ATOM(a, t) == key) ? TT_LEAF_TRIE(a, t) : TT_NO_PTR;
}

static tt_node_ptr_t splice_key(tt_arena_t *a,
				tt_atom_t key,
				tt_node_ptr_t trie,
				unsigned int index,
				tt_node_ptr_t sib)
{
  if (bit_ref(key, index)) {
    return tt_cons_node(a, index, sib, RET_IF_NO_PTR(tt_cons_leaf(a, trie, key)));
  } else {
    return tt_cons_node(a, index, RET_IF_NO_PTR(tt_cons_leaf(a, trie, key)), sib);
  }
}

static int set_walk(tt_arena_t *a,
		    tt_atom_t key,
		    tt_node_ptr_t trie,
		    tt_node_ptr_t n,
		    tt_node_ptr_t *result)
{
  switch (tt_ptr_tag(n)) {
    case TT_TAG_LEAF: {
      tt_atom_t differences = key ^ TT_LEAF_ATOM(a, n);
      if (differences == 0) {
	/* Keys identical. If values identical, just return this node. */
	if (TT_LEAF_TRIE(a, n) == trie) {
	  *result = n;
	  return -1;
	} else {
	  *result = tt_cons_leaf(a, trie, key);
	  return -1;
	}
      } else {
	int leading_zeros = __builtin_clz(differences);
	int first_differing_bit = (8 * sizeof(differences)) - leading_zeros - 1;
	return first_differing_bit;
      }
    }
    case TT_TAG_NODE: {
      int index = TT_NODE_INDEX(a, n);
      if (bit_ref(key, index)) {
	tt_node_ptr_t one = TT_NODE_ONE(a, n);
	int first_differing_bit = set_walk(a, key, trie, one, result);
	if (first_differing_bit == -1) {
	  if (*result == one) {
	    *result = n;
	  } else if (*result == TT_NO_PTR) {
	    /* Do nothing. */
	  } else {
	    *result = tt_cons_node(a, index, TT_NODE_ZERO(a, n), *result);
	  }
	  return -1;
	} else if (first_differing_bit > index) {
	  return first_differing_bit;
	} else {
	  *result = splice_key(a, key, trie, first_differing_bit, one);
	  if (*result != TT_NO_PTR) {
	    *result = tt_cons_node(a, index, TT_NODE_ZERO(a, n), *result);
	  }
	  return -1;
	}
      } else {
	tt_node_ptr_t zero = TT_NODE_ZERO(a, n);
	int first_differing_bit = set_walk(a, key, trie, zero, result);
	if (first_differing_bit == -1) {
	  if (*result == zero) {
	    *result = n;
	  } else if (*result == TT_NO_PTR) {
	    /* Do nothing. */
	  } else {
	    *result = tt_cons_node(a, index, *result, TT_NODE_ONE(a, n));
	  }
	  return -1;
	} else if (first_differing_bit > index) {
	  return first_differing_bit;
	} else {
	  *result = splice_key(a, key, trie, first_differing_bit, zero);
	  if (*result != TT_NO_PTR) {
	    *result = tt_cons_node(a, index, *result, TT_NODE_ONE(a, n));
	  }
	  return -1;
	}
      }
    }
    default:
      assert(0);
  }
}

tt_node_ptr_t tt_dict_set(tt_arena_t *a,
			  tt_node_ptr_t t,
			  tt_atom_t key,
			  tt_node_ptr_t trie)
{
  if (t == TT_EMPTY) {
    return tt_cons_dict(a, RET_IF_NO_PTR(tt_cons_leaf(a, trie, key)), 1);
  }

  assert(tt_ptr_tag(t) == TT_TAG_DICT);

  {
    tt_node_ptr_t result = TT_NO_PTR;
    int first_differing_bit = set_walk(a, key, trie, TT_DICT_ROOT(a,t), &result);
    if (first_differing_bit != -1) {
      result = splice_key(a, key, trie, first_differing_bit, TT_DICT_ROOT(a,t));
    }
    if (result == TT_NO_PTR) {
      return TT_NO_PTR;
    } else {
      return tt_cons_dict(a, result, TT_DICT_SIZE(a,t) + 1);
    }
  }
}

tt_node_ptr_t tt_dict_remove1(tt_arena_t *a,
			      tt_node_ptr_t n,
			      tt_atom_t key,
			      int *removed_count)
{
  switch (tt_ptr_tag(n)) {
    case TT_TAG_LEAF: {
      if (TT_LEAF_ATOM(a,n) == key) {
	*removed_count = 1;
	return TT_EMPTY;
      } else {
	return n;
      }
    }
    case TT_TAG_NODE: {
      int index = TT_NODE_INDEX(a,n);
      if (bit_ref(key, index)) {
	tt_node_ptr_t n1 =
	  RET_IF_NO_PTR(tt_dict_remove1(a, TT_NODE_ONE(a,n), key, removed_count));
	if (n1 == TT_EMPTY) {
	  return TT_NODE_ZERO(a,n);
	} else {
	  return tt_cons_node(a, index, TT_NODE_ZERO(a,n), n1);
	}
      } else {
	tt_node_ptr_t n1 =
	  RET_IF_NO_PTR(tt_dict_remove1(a, TT_NODE_ZERO(a,n), key, removed_count));
	if (n1 == TT_EMPTY) {
	  return TT_NODE_ONE(a,n);
	} else {
	  return tt_cons_node(a, index, n1, TT_NODE_ONE(a,n));
	}
      }
    }
    default:
      assert(0);
  }
}

tt_node_ptr_t tt_dict_remove(tt_arena_t *a,
			     tt_node_ptr_t t,
			     tt_atom_t key)
{
  if (t == TT_EMPTY) {
    return TT_EMPTY;
  }

  assert(tt_ptr_tag(t) == TT_TAG_DICT);

  {
    int removed_count = 0;
    tt_node_ptr_t n =
      RET_IF_NO_PTR(tt_dict_remove1(a, TT_DICT_ROOT(a,t), key, &removed_count));
    if (n == TT_EMPTY) {
      return TT_EMPTY;
    } else {
      return tt_cons_dict(a, n, TT_DICT_SIZE(a,t) - removed_count);
    }
  }
}

void tt_dict_foreach1(tt_arena_t *a,
		 tt_node_ptr_t n,
		 void *context,
		 void (*f)(void *context, tt_atom_t key, tt_node_ptr_t trie))
{
  switch (tt_ptr_tag(n)) {
    case TT_TAG_LEAF: {
      f(context, TT_LEAF_ATOM(a,n), TT_LEAF_TRIE(a,n));
      break;
    }
    case TT_TAG_NODE: {
      tt_dict_foreach1(a, TT_NODE_ZERO(a,n), context, f);
      tt_dict_foreach1(a, TT_NODE_ONE(a,n), context, f);
      break;
    }
    default:
      assert(0);
  }
}

void tt_dict_foreach(tt_arena_t *a,
		     tt_node_ptr_t t,
		     void *context,
		     void (*f)(void *, tt_atom_t key, tt_node_ptr_t trie))
{
  if (t != TT_EMPTY) {
    assert(tt_ptr_tag(t) == TT_TAG_DICT);
    tt_dict_foreach1(a, TT_DICT_ROOT(a,t), context, f);
  }
}