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[mLib] / sym.c

/* -*-c-*-
 *
 * $Id: sym.c,v 1.1 1998/06/17 23:44:42 mdw Exp $
 *
 * Symbol table management
 *
 * (c) 1998 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------*
 *
 * This file is part of the mLib utilities library.
 *
 * mLib is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * mLib is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with mLib; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------*
 *
 * $Log: sym.c,v $
 * Revision 1.1  1998/06/17 23:44:42  mdw
 * Initial revision
 *
 */

/*----- Header files ------------------------------------------------------*/

/* --- ANSI headers --- */

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

/* --- Local headers --- */

#include "alloc.h"
#include "crc32.h"
#include "exc.h"
#include "sub.h"
#include "sym.h"
#include "track.h"

/*----- Tuning parameters -------------------------------------------------*/

/* --- Initial hash table size --- *
 *
 * This is the initial @mask@ value.  It must be of the form %$2^n - 1$%,
 * so that it can be used to mask of the bottom bits of a hash value.
 */

#define SYM_INITSZ 255			/* Size of a new hash table */

/* --- Maximum load factor --- *
 *
 * This parameter controls how much the table has to be loaded before the
 * table is extended.  The number of elements %$n$%, the number of bins %$b$%
 * and the limit %$l$% satisfy the relation %$n < bl$%; if a new item is
 * added to the table and this relation is found to be false, the table is
 * doubled in size.
 *
 * The current function gives %$l = {3n \over 4}$%, which appears to be
 * reasonable on the face of things.
 */

#define SYM_LIMIT(n) (((n) * 3) >> 2)	/* Load factor for growing table */

/*----- Useful macros -----------------------------------------------------*/

#define SYM_NAME(sy)							\
  ((sy)->len > SYM_BUFSZ ? (sy)->name.p : (sy)->name.b)

/*----- Main code ---------------------------------------------------------*/

/* --- @sym_createTable@ --- *
 *
 * Arguments:	@sym_table *t@ = symbol table to initialise
 *
 * Returns:	---
 *
 * Use:		Initialises the given symbol table.  Raises @EXC_NOMEM@ if
 *		there isn't enough memory.
 */

void sym_createTable(sym_table *t)
{
  size_t i;

  TRACK_CTX("symbol table creation");
  TRACK_PUSH;

  t->mask = SYM_INITSZ;
  t->c = SYM_LIMIT(SYM_INITSZ);
  t->a = xmalloc((t->mask + 1) * sizeof(sym_base *));

  for (i = 0; i < SYM_INITSZ + 1; i++)
    t->a[i] = 0;

  TRACK_POP;
}

/* --- @sym_destroyTable@ --- *
 *
 * Arguments:	@sym_table *t@ = pointer to symbol table in question
 *
 * Returns:	---
 *
 * Use:		Destroys a symbol table, freeing all the memory it used to
 *		occupy.
 */

void sym_destroyTable(sym_table *t)
{
  size_t i;
  sym_base *p, *q;

  TRACK_CTX("symbol table deletion");
  TRACK_PUSH;

  for (i = 0; i <= t->mask; i++) {
    p = t->a[i];
    while (p) {
      q = p->next;
      if (p->len > SYM_BUFSZ)
	sub_free(p->name.p, p->len);
      free(p);
      p = q;
    }
  }
  free(t->a);

  TRACK_POP;
}

/* --- @sym_find@ --- *
 *
 * Arguments:	@sym_table *t@ = pointer to symbol table in question
 *		@const char *n@ = pointer to symbol table to look up
 *		@long l@ = length of the name string or negative to measure
 *		@size_t sz@ = size of desired symbol object, or zero
 *		@unsigned *f@ = pointer to a flag, or null.
 *
 * Returns:	The address of a @sym_base@ structure, or null if not found
 *		and @sz@ is zero.
 *
 * Use:		Looks up a symbol in a given symbol table.  The name is
 *		passed by the address of its first character.  The length
 *		may be given, in which case the name may contain arbitrary
 *		binary data, or it may be given as a negative number, in
 *		which case the length of the name is calculated as
 *		@strlen(n) + 1@.
 *
 *		The return value is the address of a pointer to a @sym_base@
 *		block (which may have other things on the end, as above).  If
 *		the symbol could be found, the return value points to the
 *		symbol block.  If the symbol wasn't there, then if @sz@ is
 *		nonzero, a new symbol is created and its address is returned;
 *		otherwise a null pointer is returned.  The exception
 *		@EXC_NOMEM@ is raised if the block can't be allocated.
 *
 *		The value of @*f@ indicates whether a new symbol entry was
 *		created: a nonzero value indicates that an old value was
 *		found.
 */

void *sym_find(sym_table *t, const char *n, long l, size_t sz, unsigned *f)
{
  unsigned long hash;			/* Hash value for user's name */
  size_t len = l < 0 ? strlen(n) + 1 : l; /* Find length of user's name */
  sym_base *bin;			/* Bin containing our item */
  sym_base *p, *q;			/* Pointer wandering through list */

  /* --- Find the correct bin --- */

  CRC32(hash, 0, n, len);		/* Find hash value for this name */
  bin = p = (sym_base *)(t->a + (hash & t->mask));

  /* --- Search the bin list --- */

  while (p->next) {
    if (hash == p->next->hash &&	/* Check full hash values first */
	len == p->next->len &&		/* Then compare string lengths */
	!memcmp(n, SYM_NAME(p->next), len)) /* And finally compare names */
    {
      /* --- Found a match --- *
       *
       * As a minor, and probably pointless, tweak, move the item to the
       * front of its bin list.
       */

      q = p->next;			/* Find the actual symbol block */
      p->next = q->next;		/* Extract block from bin list */
      q->next = bin->next;		/* Set up symbol's next pointer */
      bin->next = q;			/* And reinsert the block */

      /* --- Return the block --- */

      if (f) *f = 1;			/* Didn't fail to find the item */
      return (q);			/* And return the block */
    }

    p = p->next;			/* Move onto the next item */
  }

  /* --- Couldn't find the item there --- */

  if (f) *f = 0;			/* Failed to find the block */
  if (!sz) return (0);			/* Return zero if not creating */

  /* --- Create a new symbol block and initialise it --- */

  {
    TRACK_CTX("new symbol creation");
    TRACK_PUSH;

    p = xmalloc(sz);			/* Create a new symbol block */
    p->next = bin->next;		/* Set up the next pointer */
    p->hash = hash;			/* Set up the hash value too */
    p->len = len;			/* And set up the string length */
    if (len <= SYM_BUFSZ)
      memcpy(p->name.b, n, len);	/* And copy the string over */
    else {
      TRY {
	p->name.p = sub_alloc(len);	/* Allocate a block for the name */
	memcpy(p->name.p, n, len);	/* And copy the string over */
      } CATCH {
	free(p);
	TRACK_POP;
	RETHROW;
      } END_TRY;
    }

    TRACK_POP;
  }

  bin->next = p;			/* Put the pointer into the bin */

  /* --- Consider growing the array --- */

  if (!--t->c) {
    unsigned long m = t->mask + 1;	/* Next set bit in has word */
    sym_base *p, *q, *r;		/* More useful pointers */
    size_t i, lim;			/* Loop counter and limit */

    TRACK_CTX("symbol table extension");
    TRACK_PUSH;

    /* --- Update values in the anchor block --- */

    TRY {
      t->a = xrealloc(t->a, (t->mask + 1) * 2 * sizeof(sym_base *));
    } CATCH switch (exc_type) {
      case EXC_NOMEM:
	TRACK_POP;
	return (p);
      default:
	TRACK_POP;
	RETHROW;
    } END_TRY;

    t->c = SYM_LIMIT(t->mask + 1);	/* Set load value */
    t->mask = (t->mask + 1) * 2 - 1;	/* Set the new mask value */

    /* --- Now wander through the table rehashing things --- *
     *
     * This loop is very careful to avoid problems with aliasing.  The items
     * are dealt with from the end backwards to avoid overwriting bins before
     * they've been processed.
     */

    lim = (t->mask + 1) >> 1;
    for (i = 0; i < lim; i++) {

      /* --- Some initialisation --- */

      r = t->a[i];			/* Find the list we're dissecting */
      p = (sym_base *)(t->a + i);	/* Find bit-clear list */
      q = (sym_base *)(t->a + i + lim);	/* And the bit-set lsit */

      /* --- Now go through the @r@ list --- */

      while (r) {
	if (r->hash & m)		/* Is the next bit set? */
	  q = q->next = r;		/* Yes, so fit up previous link */
	else
	  p = p->next = r;		/* No, so fit up previous link */
	r = r->next;			/* Move onto the next item */
      }
      p->next = q->next = 0;		/* Null terminate the new lists */
    }

    TRACK_POP;
  }

  /* --- Finished that, so return the new symbol block --- */

  return (p);
}

/* --- @sym_remove@ --- *
 *
 * Arguments:	@sym_table *i@ = pointer to a symbol table object
 *		@void *b@ = pointer to symbol table entry
 *
 * Returns:	---
 *
 * Use:		Removes the object from the symbol table.  The space occupied
 *		by the object and its name is freed; anything else attached
 *		to the entry should already be gone by this point.
 */

void sym_remove(sym_table *t, void *b)
{
  /* --- A quick comment --- *
   *
   * Since the @sym_base@ block contains the hash, finding the element in the
   * bin list is really quick -- it's not worth bothering with things like
   * doubly linked lists.
   */

  sym_base *p = b;
  sym_base *bin = (sym_base *)(t->a + (p->hash & t->mask));

  /* --- Find the item in the bin list --- */

  while (bin->next) {
    if (bin->next == p)
      break;
    bin = bin->next;
  }
  if (!bin->next)
    return;

  /* --- Now just remove the item from the list and free it --- *
   *
   * Oh, and bump the load counter.
   */

  bin->next = p->next;
  if (p->len > SYM_BUFSZ)
    sub_free(p->name.p, p->len);
  free(p);
  t->c++;
}

/* --- @sym_createIter@ --- *
 *
 * Arguments:	@sym_iter *i@ = pointer to an iterator object
 *		@sym_table *t@ = pointer to a symbol table object
 *
 * Returns:	---
 *
 * Use:		Creates a new symbol table iterator which may be used to
 *		iterate through a symbol table.
 */

void sym_createIter(sym_iter *i, sym_table *t)
{
  i->t = t;
  i->i = 0;
  i->n = 0;
}

/* --- @sym_next@ --- *
 *
 * Arguments:	@sym_iter *i@ = pointer to iterator object
 *
 * Returns:	Pointer to the next symbol found, or null when finished.
 *
 * Use:		Returns the next symbol from the table.  Symbols are not
 *		returned in any particular order.
 */

void *sym_next(sym_iter *i)
{
  sym_base *p;

  /* --- Find the next item --- */

  while (!i->n) {
    if (i->i > i->t->mask)
      return (0);
    i->n = i->t->a[i->i++];
  }

  /* --- Update the iterator block --- */

  p = i->n;
  i->n = p->next;

  /* --- Done --- */

  return (p);
}

/*----- Symbol table test code --------------------------------------------*/

#ifdef TEST_RIG

#include <errno.h>
#include <time.h>

typedef struct sym_word {
  sym_base base;
  size_t i;
} sym_word;


/* --- What it does --- *
 *
 * Reads the file /usr/dict/words (change to some other file full of
 * interesting and appropriate bits of text to taste) into a big buffer and
 * picks apart into lines.  Then picks lines at random and enters them into
 * the symbol table.
 */

int main(void)
{
  char *buff, *p, *lim;
  size_t sz, done;
  FILE *fp;
  int i;
  char **line;
  sym_word **flag;
  sym_table tbl;
  int entries;

  /* --- Initialise for reading the file --- */

  sz = BUFSIZ;
  buff = xmalloc(sz + 1);
  done = 0;
  sub_init();

  if ((fp = fopen("/usr/dict/words", "r")) == 0)
    fprintf(stderr, "buggered ;-( (%s)\n", strerror(errno));

  /* --- Read buffers of text --- *
   *
   * Read a buffer.  If more to come, double the buffer size and try again.
   * This is the method I recommended to comp.lang.c, so I may as well try
   * it.
   */

  for (;;) {
    i = fread(buff + done, 1, sz - done, fp);
    done += i;
    if (done != sz)
      break;
    sz <<= 1;
    buff = xrealloc(buff, sz + 1);
  }

  /* --- Count the lines --- */

  lim = buff + done;

  sz = 1;
  for (p = buff; p < lim; p++)
    if (*p == '\n') sz++;

  /* --- Build a table of line starts --- */

  line = xmalloc(sz * sizeof(char *));
  i = 0;
  line[i++] = buff;
  for (p = buff; p < lim; p++)
    if (*p == '\n') *p = 0, line[i++] = p + 1;
  *lim = 0;

  /* --- Build a table of lines --- *
   *
   * This reverses the mapping which the symbol table performs, so that its
   * accuracy can be tested.
   */

  flag = xmalloc(sz * sizeof(sym_word *));
  for (i = 0; i < sz; i++)
    flag[i] = 0;
  entries = 0;

  sym_createTable(&tbl);

  for (;;) {
    i = (unsigned)rand() % sz;

    switch (rand() % 5)
    {
      case 0: {
	sym_word *w;

	printf("find `%s'\n", line[i]);
	if ((rand() & 1023) == 0) {
	  putchar('.'); fflush(stdout);
	}

	w = sym_find(&tbl, line[i], -1, 0, 0);
	if (w != flag[i])
	  printf("*** error: find `%s' gave %p not %p\n",
		 line[i], (void *)w, (void *)flag[i]);
	else if (w && w->i != i)
	  printf("*** error: find sym for `%s' gives index %i not %i\n",
		 line[i], w->i, i);	
      } break;

      case 1: {
	unsigned f;
	sym_word *w;

	printf("create `%s'\n", line[i]);
	if ((rand() & 1023) == 0) {
	  putchar('+'); fflush(stdout);
	}

	w = sym_find(&tbl, line[i], -1, sizeof(sym_word), &f);
	if (f)
	{
	  if (w != flag[i])
	    printf("*** error: create `%s' gave %p not %p\n",
		   line[i], (void *)w, (void *)flag[i]);
	  else if (w && w->i != i)
	    printf("*** error: create sym for `%s' gives index %i not %i\n",
		   line[i], w->i, i);
	}
	else
	{
	  if (flag[i])
	    printf("*** error: create `%s' gave new block, should be %p\n",
		   line[i], (void *)flag[i]);
	  else {
	    flag[i] = w;
	    w->i = i;
	    entries++;
	  }
	}
      } break;

      case 2: {
	sym_iter it;
	sym_word *w, **ntbl;
	int v;

	if (!entries)
	  break;
	v = (rand() % entries) == 0;
	if (!v)
	  break;
	printf("\niterated %i entries\n", entries);
	break;

	printf("iterate\n");

	ntbl = xmalloc(sz * sizeof(sym_word *));
	memcpy(ntbl, flag, sz * sizeof(sym_word *));
	sym_createIter(&it, &tbl);

	while ((w = sym_next(&it)) != 0) {
	  if (ntbl[w->i] == 0)
	    printf("*** error: iterate returned duff item %i\n", w->i);
	  else
	    ntbl[w->i] = 0;
	}

	for (i = 0; i < sz; i++)
	  if (ntbl[i]) printf("*** error: iterate didn't return item %i\n",
			      i);
	free(ntbl);
      } break;

      case 3: {
	sym_base *b;
	int v = rand() & 255 ? 0 : 1;
	break;

	printf("dump\n");

	for (i = 0; i <= tbl.mask; i++) {
	  if (!tbl.a[i]) continue;
	  if (v) printf("  %i: ", i);
	  b = tbl.a[i];
	  while (b) {
	    if ((b->hash & tbl.mask) != i)
	      printf("*** error: bad hash value found");
	    if (v) printf("`%s'(%08lx:%lu) ",
			  line[((sym_word *)b)->i],
			  b->hash,
			  b->hash & tbl.mask);
	    b = b->next;
	  }
	  if (v) putchar('\n');
	}
      } break;

      case 4: {
	if (flag[i]) {
	  printf("remove `%s'\n", SYM_NAME(&flag[i]->base));
	  if ((rand() & 1023) == 0) {
	    putchar('-'); fflush(stdout);
	  }
	  sym_remove(&tbl, flag[i]);
	  flag[i] = 0;
	  entries--;
	}
      } break;
    }

  }

  return (0);
}

#endif

/*----- That's all, folks -------------------------------------------------*/