bfd/hash.c

   1 /* hash.c -- hash table routines for BFD
   2    Copyright 1993, 1994, 1995, 1997, 1999, 2001, 2002, 2003, 2004, 2005,
   3    2006, 2007, 2009, 2010, 2011  Free Software Foundation, Inc.
   4    Written by Steve Chamberlain <sac@cygnus.com>
   5
   6    This file is part of BFD, the Binary File Descriptor library.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program; if not, write to the Free Software
  20    Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21    MA 02110-1301, USA.  */
  22
  23 #include "sysdep.h"
  24 #include "bfd.h"
  25 #include "libbfd.h"
  26 #include "objalloc.h"
  27 #include "libiberty.h"
  28
  29 /*
  30 SECTION
  31         Hash Tables
  32
  33 @cindex Hash tables
  34         BFD provides a simple set of hash table functions.  Routines
  35         are provided to initialize a hash table, to free a hash table,
  36         to look up a string in a hash table and optionally create an
  37         entry for it, and to traverse a hash table.  There is
  38         currently no routine to delete an string from a hash table.
  39
  40         The basic hash table does not permit any data to be stored
  41         with a string.  However, a hash table is designed to present a
  42         base class from which other types of hash tables may be
  43         derived.  These derived types may store additional information
  44         with the string.  Hash tables were implemented in this way,
  45         rather than simply providing a data pointer in a hash table
  46         entry, because they were designed for use by the linker back
  47         ends.  The linker may create thousands of hash table entries,
  48         and the overhead of allocating private data and storing and
  49         following pointers becomes noticeable.
  50
  51         The basic hash table code is in <<hash.c>>.
  52
  53 @menu
  54 @* Creating and Freeing a Hash Table::
  55 @* Looking Up or Entering a String::
  56 @* Traversing a Hash Table::
  57 @* Deriving a New Hash Table Type::
  58 @end menu
  59
  60 INODE
  61 Creating and Freeing a Hash Table, Looking Up or Entering a String, Hash Tables, Hash Tables
  62 SUBSECTION
  63         Creating and freeing a hash table
  64
  65 @findex bfd_hash_table_init
  66 @findex bfd_hash_table_init_n
  67         To create a hash table, create an instance of a <<struct
  68         bfd_hash_table>> (defined in <<bfd.h>>) and call
  69         <<bfd_hash_table_init>> (if you know approximately how many
  70         entries you will need, the function <<bfd_hash_table_init_n>>,
  71         which takes a @var{size} argument, may be used).
  72         <<bfd_hash_table_init>> returns <<FALSE>> if some sort of
  73         error occurs.
  74
  75 @findex bfd_hash_newfunc
  76         The function <<bfd_hash_table_init>> take as an argument a
  77         function to use to create new entries.  For a basic hash
  78         table, use the function <<bfd_hash_newfunc>>.  @xref{Deriving
  79         a New Hash Table Type}, for why you would want to use a
  80         different value for this argument.
  81
  82 @findex bfd_hash_allocate
  83         <<bfd_hash_table_init>> will create an objalloc which will be
  84         used to allocate new entries.  You may allocate memory on this
  85         objalloc using <<bfd_hash_allocate>>.
  86
  87 @findex bfd_hash_table_free
  88         Use <<bfd_hash_table_free>> to free up all the memory that has
  89         been allocated for a hash table.  This will not free up the
  90         <<struct bfd_hash_table>> itself, which you must provide.
  91
  92 @findex bfd_hash_set_default_size
  93         Use <<bfd_hash_set_default_size>> to set the default size of
  94         hash table to use.
  95
  96 INODE
  97 Looking Up or Entering a String, Traversing a Hash Table, Creating and Freeing a Hash Table, Hash Tables
  98 SUBSECTION
  99         Looking up or entering a string
 100
 101 @findex bfd_hash_lookup
 102         The function <<bfd_hash_lookup>> is used both to look up a
 103         string in the hash table and to create a new entry.
 104
 105         If the @var{create} argument is <<FALSE>>, <<bfd_hash_lookup>>
 106         will look up a string.  If the string is found, it will
 107         returns a pointer to a <<struct bfd_hash_entry>>.  If the
 108         string is not found in the table <<bfd_hash_lookup>> will
 109         return <<NULL>>.  You should not modify any of the fields in
 110         the returns <<struct bfd_hash_entry>>.
 111
 112         If the @var{create} argument is <<TRUE>>, the string will be
 113         entered into the hash table if it is not already there.
 114         Either way a pointer to a <<struct bfd_hash_entry>> will be
 115         returned, either to the existing structure or to a newly
 116         created one.  In this case, a <<NULL>> return means that an
 117         error occurred.
 118
 119         If the @var{create} argument is <<TRUE>>, and a new entry is
 120         created, the @var{copy} argument is used to decide whether to
 121         copy the string onto the hash table objalloc or not.  If
 122         @var{copy} is passed as <<FALSE>>, you must be careful not to
 123         deallocate or modify the string as long as the hash table
 124         exists.
 125
 126 INODE
 127 Traversing a Hash Table, Deriving a New Hash Table Type, Looking Up or Entering a String, Hash Tables
 128 SUBSECTION
 129         Traversing a hash table
 130
 131 @findex bfd_hash_traverse
 132         The function <<bfd_hash_traverse>> may be used to traverse a
 133         hash table, calling a function on each element.  The traversal
 134         is done in a random order.
 135
 136         <<bfd_hash_traverse>> takes as arguments a function and a
 137         generic <<void *>> pointer.  The function is called with a
 138         hash table entry (a <<struct bfd_hash_entry *>>) and the
 139         generic pointer passed to <<bfd_hash_traverse>>.  The function
 140         must return a <<boolean>> value, which indicates whether to
 141         continue traversing the hash table.  If the function returns
 142         <<FALSE>>, <<bfd_hash_traverse>> will stop the traversal and
 143         return immediately.
 144
 145 INODE
 146 Deriving a New Hash Table Type, , Traversing a Hash Table, Hash Tables
 147 SUBSECTION
 148         Deriving a new hash table type
 149
 150         Many uses of hash tables want to store additional information
 151         which each entry in the hash table.  Some also find it
 152         convenient to store additional information with the hash table
 153         itself.  This may be done using a derived hash table.
 154
 155         Since C is not an object oriented language, creating a derived
 156         hash table requires sticking together some boilerplate
 157         routines with a few differences specific to the type of hash
 158         table you want to create.
 159
 160         An example of a derived hash table is the linker hash table.
 161         The structures for this are defined in <<bfdlink.h>>.  The
 162         functions are in <<linker.c>>.
 163
 164         You may also derive a hash table from an already derived hash
 165         table.  For example, the a.out linker backend code uses a hash
 166         table derived from the linker hash table.
 167
 168 @menu
 169 @* Define the Derived Structures::
 170 @* Write the Derived Creation Routine::
 171 @* Write Other Derived Routines::
 172 @end menu
 173
 174 INODE
 175 Define the Derived Structures, Write the Derived Creation Routine, Deriving a New Hash Table Type, Deriving a New Hash Table Type
 176 SUBSUBSECTION
 177         Define the derived structures
 178
 179         You must define a structure for an entry in the hash table,
 180         and a structure for the hash table itself.
 181
 182         The first field in the structure for an entry in the hash
 183         table must be of the type used for an entry in the hash table
 184         you are deriving from.  If you are deriving from a basic hash
 185         table this is <<struct bfd_hash_entry>>, which is defined in
 186         <<bfd.h>>.  The first field in the structure for the hash
 187         table itself must be of the type of the hash table you are
 188         deriving from itself.  If you are deriving from a basic hash
 189         table, this is <<struct bfd_hash_table>>.
 190
 191         For example, the linker hash table defines <<struct
 192         bfd_link_hash_entry>> (in <<bfdlink.h>>).  The first field,
 193         <<root>>, is of type <<struct bfd_hash_entry>>.  Similarly,
 194         the first field in <<struct bfd_link_hash_table>>, <<table>>,
 195         is of type <<struct bfd_hash_table>>.
 196
 197 INODE
 198 Write the Derived Creation Routine, Write Other Derived Routines, Define the Derived Structures, Deriving a New Hash Table Type
 199 SUBSUBSECTION
 200         Write the derived creation routine
 201
 202         You must write a routine which will create and initialize an
 203         entry in the hash table.  This routine is passed as the
 204         function argument to <<bfd_hash_table_init>>.
 205
 206         In order to permit other hash tables to be derived from the
 207         hash table you are creating, this routine must be written in a
 208         standard way.
 209
 210         The first argument to the creation routine is a pointer to a
 211         hash table entry.  This may be <<NULL>>, in which case the
 212         routine should allocate the right amount of space.  Otherwise
 213         the space has already been allocated by a hash table type
 214         derived from this one.
 215
 216         After allocating space, the creation routine must call the
 217         creation routine of the hash table type it is derived from,
 218         passing in a pointer to the space it just allocated.  This
 219         will initialize any fields used by the base hash table.
 220
 221         Finally the creation routine must initialize any local fields
 222         for the new hash table type.
 223
 224         Here is a boilerplate example of a creation routine.
 225         @var{function_name} is the name of the routine.
 226         @var{entry_type} is the type of an entry in the hash table you
 227         are creating.  @var{base_newfunc} is the name of the creation
 228         routine of the hash table type your hash table is derived
 229         from.
 230
 231 EXAMPLE
 232
 233 .struct bfd_hash_entry *
 234 .@var{function_name} (struct bfd_hash_entry *entry,
 235 .                     struct bfd_hash_table *table,
 236 .                     const char *string)
 237 .{
 238 .  struct @var{entry_type} *ret = (@var{entry_type} *) entry;
 239 .
 240 . {* Allocate the structure if it has not already been allocated by a
 241 .    derived class.  *}
 242 .  if (ret == NULL)
 243 .    {
 244 .      ret = bfd_hash_allocate (table, sizeof (* ret));
 245 .      if (ret == NULL)
 246 .        return NULL;
 247 .    }
 248 .
 249 . {* Call the allocation method of the base class.  *}
 250 .  ret = ((@var{entry_type} *)
 251 .        @var{base_newfunc} ((struct bfd_hash_entry *) ret, table, string));
 252 .
 253 . {* Initialize the local fields here.  *}
 254 .
 255 .  return (struct bfd_hash_entry *) ret;
 256 .}
 257
 258 DESCRIPTION
 259         The creation routine for the linker hash table, which is in
 260         <<linker.c>>, looks just like this example.
 261         @var{function_name} is <<_bfd_link_hash_newfunc>>.
 262         @var{entry_type} is <<struct bfd_link_hash_entry>>.
 263         @var{base_newfunc} is <<bfd_hash_newfunc>>, the creation
 264         routine for a basic hash table.
 265
 266         <<_bfd_link_hash_newfunc>> also initializes the local fields
 267         in a linker hash table entry: <<type>>, <<written>> and
 268         <<next>>.
 269
 270 INODE
 271 Write Other Derived Routines, , Write the Derived Creation Routine, Deriving a New Hash Table Type
 272 SUBSUBSECTION
 273         Write other derived routines
 274
 275         You will want to write other routines for your new hash table,
 276         as well.
 277
 278         You will want an initialization routine which calls the
 279         initialization routine of the hash table you are deriving from
 280         and initializes any other local fields.  For the linker hash
 281         table, this is <<_bfd_link_hash_table_init>> in <<linker.c>>.
 282
 283         You will want a lookup routine which calls the lookup routine
 284         of the hash table you are deriving from and casts the result.
 285         The linker hash table uses <<bfd_link_hash_lookup>> in
 286         <<linker.c>> (this actually takes an additional argument which
 287         it uses to decide how to return the looked up value).
 288
 289         You may want a traversal routine.  This should just call the
 290         traversal routine of the hash table you are deriving from with
 291         appropriate casts.  The linker hash table uses
 292         <<bfd_link_hash_traverse>> in <<linker.c>>.
 293
 294         These routines may simply be defined as macros.  For example,
 295         the a.out backend linker hash table, which is derived from the
 296         linker hash table, uses macros for the lookup and traversal
 297         routines.  These are <<aout_link_hash_lookup>> and
 298         <<aout_link_hash_traverse>> in aoutx.h.
 299 */
 300
 301 /* The default number of entries to use when creating a hash table.  */
 302 #define DEFAULT_SIZE 4051
 303
 304 /* The following function returns a nearest prime number which is
 305    greater than N, and near a power of two.  Copied from libiberty.
 306    Returns zero for ridiculously large N to signify an error.  */
 307
 308 static unsigned long
 309 higher_prime_number (unsigned long n)
 310 {
 311   /* These are primes that are near, but slightly smaller than, a
 312      power of two.  */
 313   static const unsigned long primes[] =
 314     {
 315       (unsigned long) 31,
 316       (unsigned long) 61,
 317       (unsigned long) 127,
 318       (unsigned long) 251,
 319       (unsigned long) 509,
 320       (unsigned long) 1021,
 321       (unsigned long) 2039,
 322       (unsigned long) 4093,
 323       (unsigned long) 8191,
 324       (unsigned long) 16381,
 325       (unsigned long) 32749,
 326       (unsigned long) 65521,
 327       (unsigned long) 131071,
 328       (unsigned long) 262139,
 329       (unsigned long) 524287,
 330       (unsigned long) 1048573,
 331       (unsigned long) 2097143,
 332       (unsigned long) 4194301,
 333       (unsigned long) 8388593,
 334       (unsigned long) 16777213,
 335       (unsigned long) 33554393,
 336       (unsigned long) 67108859,
 337       (unsigned long) 134217689,
 338       (unsigned long) 268435399,
 339       (unsigned long) 536870909,
 340       (unsigned long) 1073741789,
 341       (unsigned long) 2147483647,
 342                                         /* 4294967291L */
 343       ((unsigned long) 2147483647) + ((unsigned long) 2147483644),
 344   };
 345
 346   const unsigned long *low = &primes[0];
 347   const unsigned long *high = &primes[sizeof (primes) / sizeof (primes[0])];
 348
 349   while (low != high)
 350     {
 351       const unsigned long *mid = low + (high - low) / 2;
 352       if (n >= *mid)
 353         low = mid + 1;
 354       else
 355         high = mid;
 356     }
 357
 358   if (n >= *low)
 359     return 0;
 360
 361   return *low;
 362 }
 363
 364 static unsigned long bfd_default_hash_table_size = DEFAULT_SIZE;
 365
 366 /* Create a new hash table, given a number of entries.  */
 367
 368 bfd_boolean
 369 bfd_hash_table_init_n (struct bfd_hash_table *table,
 370                        struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
 371                                                           struct bfd_hash_table *,
 372                                                           const char *),
 373                        unsigned int entsize,
 374                        unsigned int size)
 375 {
 376   unsigned long alloc;
 377
 378   alloc = size;
 379   alloc *= sizeof (struct bfd_hash_entry *);
 380   if (alloc / sizeof (struct bfd_hash_entry *) != size)
 381     {
 382       bfd_set_error (bfd_error_no_memory);
 383       return FALSE;
 384     }
 385
 386   table->memory = (void *) objalloc_create ();
 387   if (table->memory == NULL)
 388     {
 389       bfd_set_error (bfd_error_no_memory);
 390       return FALSE;
 391     }
 392   table->table = (struct bfd_hash_entry **)
 393       objalloc_alloc ((struct objalloc *) table->memory, alloc);
 394   if (table->table == NULL)
 395     {
 396       bfd_set_error (bfd_error_no_memory);
 397       return FALSE;
 398     }
 399   memset ((void *) table->table, 0, alloc);
 400   table->size = size;
 401   table->entsize = entsize;
 402   table->count = 0;
 403   table->frozen = 0;
 404   table->newfunc = newfunc;
 405   return TRUE;
 406 }
 407
 408 /* Create a new hash table with the default number of entries.  */
 409
 410 bfd_boolean
 411 bfd_hash_table_init (struct bfd_hash_table *table,
 412                      struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
 413                                                         struct bfd_hash_table *,
 414                                                         const char *),
 415                      unsigned int entsize)
 416 {
 417   return bfd_hash_table_init_n (table, newfunc, entsize,
 418                                 bfd_default_hash_table_size);
 419 }
 420
 421 /* Free a hash table.  */
 422
 423 void
 424 bfd_hash_table_free (struct bfd_hash_table *table)
 425 {
 426   objalloc_free ((struct objalloc *) table->memory);
 427   table->memory = NULL;
 428 }
 429
 430 static inline unsigned long
 431 bfd_hash_hash (const char *string, unsigned int *lenp)
 432 {
 433   const unsigned char *s;
 434   unsigned long hash;
 435   unsigned int len;
 436   unsigned int c;
 437
 438   hash = 0;
 439   len = 0;
 440   s = (const unsigned char *) string;
 441   while ((c = *s++) != '\0')
 442     {
 443       hash += c + (c << 17);
 444       hash ^= hash >> 2;
 445     }
 446   len = (s - (const unsigned char *) string) - 1;
 447   hash += len + (len << 17);
 448   hash ^= hash >> 2;
 449   if (lenp != NULL)
 450     *lenp = len;
 451   return hash;
 452 }
 453
 454 /* Look up a string in a hash table.  */
 455
 456 struct bfd_hash_entry *
 457 bfd_hash_lookup (struct bfd_hash_table *table,
 458                  const char *string,
 459                  bfd_boolean create,
 460                  bfd_boolean copy)
 461 {
 462   unsigned long hash;
 463   struct bfd_hash_entry *hashp;
 464   unsigned int len;
 465   unsigned int _index;
 466
 467   hash = bfd_hash_hash (string, &len);
 468   _index = hash % table->size;
 469   for (hashp = table->table[_index];
 470        hashp != NULL;
 471        hashp = hashp->next)
 472     {
 473       if (hashp->hash == hash
 474           && strcmp (hashp->string, string) == 0)
 475         return hashp;
 476     }
 477
 478   if (! create)
 479     return NULL;
 480
 481   if (copy)
 482     {
 483       char *new_string;
 484
 485       new_string = (char *) objalloc_alloc ((struct objalloc *) table->memory,
 486                                             len + 1);
 487       if (!new_string)
 488         {
 489           bfd_set_error (bfd_error_no_memory);
 490           return NULL;
 491         }
 492       memcpy (new_string, string, len + 1);
 493       string = new_string;
 494     }
 495
 496   return bfd_hash_insert (table, string, hash);
 497 }
 498
 499 /* Insert an entry in a hash table.  */
 500
 501 struct bfd_hash_entry *
 502 bfd_hash_insert (struct bfd_hash_table *table,
 503                  const char *string,
 504                  unsigned long hash)
 505 {
 506   struct bfd_hash_entry *hashp;
 507   unsigned int _index;
 508
 509   hashp = (*table->newfunc) (NULL, table, string);
 510   if (hashp == NULL)
 511     return NULL;
 512   hashp->string = string;
 513   hashp->hash = hash;
 514   _index = hash % table->size;
 515   hashp->next = table->table[_index];
 516   table->table[_index] = hashp;
 517   table->count++;
 518
 519   if (!table->frozen && table->count > table->size * 3 / 4)
 520     {
 521       unsigned long newsize = higher_prime_number (table->size);
 522       struct bfd_hash_entry **newtable;
 523       unsigned int hi;
 524       unsigned long alloc = newsize * sizeof (struct bfd_hash_entry *);
 525
 526       /* If we can't find a higher prime, or we can't possibly alloc
 527          that much memory, don't try to grow the table.  */
 528       if (newsize == 0 || alloc / sizeof (struct bfd_hash_entry *) != newsize)
 529         {
 530           table->frozen = 1;
 531           return hashp;
 532         }
 533
 534       newtable = ((struct bfd_hash_entry **)
 535                   objalloc_alloc ((struct objalloc *) table->memory, alloc));
 536       if (newtable == NULL)
 537         {
 538           table->frozen = 1;
 539           return hashp;
 540         }
 541       memset ((PTR) newtable, 0, alloc);
 542
 543       for (hi = 0; hi < table->size; hi ++)
 544         while (table->table[hi])
 545           {
 546             struct bfd_hash_entry *chain = table->table[hi];
 547             struct bfd_hash_entry *chain_end = chain;
 548
 549             while (chain_end->next && chain_end->next->hash == chain->hash)
 550               chain_end = chain_end->next;
 551
 552             table->table[hi] = chain_end->next;
 553             _index = chain->hash % newsize;
 554             chain_end->next = newtable[_index];
 555             newtable[_index] = chain;
 556           }
 557       table->table = newtable;
 558       table->size = newsize;
 559     }
 560
 561   return hashp;
 562 }
 563
 564 /* Rename an entry in a hash table.  */
 565
 566 void
 567 bfd_hash_rename (struct bfd_hash_table *table,
 568                  const char *string,
 569                  struct bfd_hash_entry *ent)
 570 {
 571   unsigned int _index;
 572   struct bfd_hash_entry **pph;
 573
 574   _index = ent->hash % table->size;
 575   for (pph = &table->table[_index]; *pph != NULL; pph = &(*pph)->next)
 576     if (*pph == ent)
 577       break;
 578   if (*pph == NULL)
 579     abort ();
 580
 581   *pph = ent->next;
 582   ent->string = string;
 583   ent->hash = bfd_hash_hash (string, NULL);
 584   _index = ent->hash % table->size;
 585   ent->next = table->table[_index];
 586   table->table[_index] = ent;
 587 }
 588
 589 /* Replace an entry in a hash table.  */
 590
 591 void
 592 bfd_hash_replace (struct bfd_hash_table *table,
 593                   struct bfd_hash_entry *old,
 594                   struct bfd_hash_entry *nw)
 595 {
 596   unsigned int _index;
 597   struct bfd_hash_entry **pph;
 598
 599   _index = old->hash % table->size;
 600   for (pph = &table->table[_index];
 601        (*pph) != NULL;
 602        pph = &(*pph)->next)
 603     {
 604       if (*pph == old)
 605         {
 606           *pph = nw;
 607           return;
 608         }
 609     }
 610
 611   abort ();
 612 }
 613
 614 /* Allocate space in a hash table.  */
 615
 616 void *
 617 bfd_hash_allocate (struct bfd_hash_table *table,
 618                    unsigned int size)
 619 {
 620   void * ret;
 621
 622   ret = objalloc_alloc ((struct objalloc *) table->memory, size);
 623   if (ret == NULL && size != 0)
 624     bfd_set_error (bfd_error_no_memory);
 625   return ret;
 626 }
 627
 628 /* Base method for creating a new hash table entry.  */
 629
 630 struct bfd_hash_entry *
 631 bfd_hash_newfunc (struct bfd_hash_entry *entry,
 632                   struct bfd_hash_table *table,
 633                   const char *string ATTRIBUTE_UNUSED)
 634 {
 635   if (entry == NULL)
 636     entry = (struct bfd_hash_entry *) bfd_hash_allocate (table,
 637                                                          sizeof (* entry));
 638   return entry;
 639 }
 640
 641 /* Traverse a hash table.  */
 642
 643 void
 644 bfd_hash_traverse (struct bfd_hash_table *table,
 645                    bfd_boolean (*func) (struct bfd_hash_entry *, void *),
 646                    void * info)
 647 {
 648   unsigned int i;
 649
 650   table->frozen = 1;
 651   for (i = 0; i < table->size; i++)
 652     {
 653       struct bfd_hash_entry *p;
 654
 655       for (p = table->table[i]; p != NULL; p = p->next)
 656         if (! (*func) (p, info))
 657           goto out;
 658     }
 659  out:
 660   table->frozen = 0;
 661 }
 662 \f
 663 unsigned long
 664 bfd_hash_set_default_size (unsigned long hash_size)
 665 {
 666   /* Extend this prime list if you want more granularity of hash table size.  */
 667   static const unsigned long hash_size_primes[] =
 668     {
 669       31, 61, 127, 251, 509, 1021, 2039, 4091, 8191, 16381, 32749, 65537
 670     };
 671   unsigned int _index;
 672
 673   /* Work out best prime number near the hash_size.  */
 674   for (_index = 0; _index < ARRAY_SIZE (hash_size_primes) - 1; ++_index)
 675     if (hash_size <= hash_size_primes[_index])
 676       break;
 677
 678   bfd_default_hash_table_size = hash_size_primes[_index];
 679   return bfd_default_hash_table_size;
 680 }
 681 \f
 682 /* A few different object file formats (a.out, COFF, ELF) use a string
 683    table.  These functions support adding strings to a string table,
 684    returning the byte offset, and writing out the table.
 685
 686    Possible improvements:
 687    + look for strings matching trailing substrings of other strings
 688    + better data structures?  balanced trees?
 689    + look at reducing memory use elsewhere -- maybe if we didn't have
 690      to construct the entire symbol table at once, we could get by
 691      with smaller amounts of VM?  (What effect does that have on the
 692      string table reductions?)  */
 693
 694 /* An entry in the strtab hash table.  */
 695
 696 struct strtab_hash_entry
 697 {
 698   struct bfd_hash_entry root;
 699   /* Index in string table.  */
 700   bfd_size_type index;
 701   /* Next string in strtab.  */
 702   struct strtab_hash_entry *next;
 703 };
 704
 705 /* The strtab hash table.  */
 706
 707 struct bfd_strtab_hash
 708 {
 709   struct bfd_hash_table table;
 710   /* Size of strtab--also next available index.  */
 711   bfd_size_type size;
 712   /* First string in strtab.  */
 713   struct strtab_hash_entry *first;
 714   /* Last string in strtab.  */
 715   struct strtab_hash_entry *last;
 716   /* Whether to precede strings with a two byte length, as in the
 717      XCOFF .debug section.  */
 718   bfd_boolean xcoff;
 719 };
 720
 721 /* Routine to create an entry in a strtab.  */
 722
 723 static struct bfd_hash_entry *
 724 strtab_hash_newfunc (struct bfd_hash_entry *entry,
 725                      struct bfd_hash_table *table,
 726                      const char *string)
 727 {
 728   struct strtab_hash_entry *ret = (struct strtab_hash_entry *) entry;
 729
 730   /* Allocate the structure if it has not already been allocated by a
 731      subclass.  */
 732   if (ret == NULL)
 733     ret = (struct strtab_hash_entry *) bfd_hash_allocate (table,
 734                                                           sizeof (* ret));
 735   if (ret == NULL)
 736     return NULL;
 737
 738   /* Call the allocation method of the superclass.  */
 739   ret = (struct strtab_hash_entry *)
 740          bfd_hash_newfunc ((struct bfd_hash_entry *) ret, table, string);
 741
 742   if (ret)
 743     {
 744       /* Initialize the local fields.  */
 745       ret->index = (bfd_size_type) -1;
 746       ret->next = NULL;
 747     }
 748
 749   return (struct bfd_hash_entry *) ret;
 750 }
 751
 752 /* Look up an entry in an strtab.  */
 753
 754 #define strtab_hash_lookup(t, string, create, copy) \
 755   ((struct strtab_hash_entry *) \
 756    bfd_hash_lookup (&(t)->table, (string), (create), (copy)))
 757
 758 /* Create a new strtab.  */
 759
 760 struct bfd_strtab_hash *
 761 _bfd_stringtab_init (void)
 762 {
 763   struct bfd_strtab_hash *table;
 764   bfd_size_type amt = sizeof (* table);
 765
 766   table = (struct bfd_strtab_hash *) bfd_malloc (amt);
 767   if (table == NULL)
 768     return NULL;
 769
 770   if (!bfd_hash_table_init (&table->table, strtab_hash_newfunc,
 771                             sizeof (struct strtab_hash_entry)))
 772     {
 773       free (table);
 774       return NULL;
 775     }
 776
 777   table->size = 0;
 778   table->first = NULL;
 779   table->last = NULL;
 780   table->xcoff = FALSE;
 781
 782   return table;
 783 }
 784
 785 /* Create a new strtab in which the strings are output in the format
 786    used in the XCOFF .debug section: a two byte length precedes each
 787    string.  */
 788
 789 struct bfd_strtab_hash *
 790 _bfd_xcoff_stringtab_init (void)
 791 {
 792   struct bfd_strtab_hash *ret;
 793
 794   ret = _bfd_stringtab_init ();
 795   if (ret != NULL)
 796     ret->xcoff = TRUE;
 797   return ret;
 798 }
 799
 800 /* Free a strtab.  */
 801
 802 void
 803 _bfd_stringtab_free (struct bfd_strtab_hash *table)
 804 {
 805   bfd_hash_table_free (&table->table);
 806   free (table);
 807 }
 808
 809 /* Get the index of a string in a strtab, adding it if it is not
 810    already present.  If HASH is FALSE, we don't really use the hash
 811    table, and we don't eliminate duplicate strings.  */
 812
 813 bfd_size_type
 814 _bfd_stringtab_add (struct bfd_strtab_hash *tab,
 815                     const char *str,
 816                     bfd_boolean hash,
 817                     bfd_boolean copy)
 818 {
 819   struct strtab_hash_entry *entry;
 820
 821   if (hash)
 822     {
 823       entry = strtab_hash_lookup (tab, str, TRUE, copy);
 824       if (entry == NULL)
 825         return (bfd_size_type) -1;
 826     }
 827   else
 828     {
 829       entry = (struct strtab_hash_entry *) bfd_hash_allocate (&tab->table,
 830                                                               sizeof (* entry));
 831       if (entry == NULL)
 832         return (bfd_size_type) -1;
 833       if (! copy)
 834         entry->root.string = str;
 835       else
 836         {
 837           char *n;
 838
 839           n = (char *) bfd_hash_allocate (&tab->table, strlen (str) + 1);
 840           if (n == NULL)
 841             return (bfd_size_type) -1;
 842           entry->root.string = n;
 843         }
 844       entry->index = (bfd_size_type) -1;
 845       entry->next = NULL;
 846     }
 847
 848   if (entry->index == (bfd_size_type) -1)
 849     {
 850       entry->index = tab->size;
 851       tab->size += strlen (str) + 1;
 852       if (tab->xcoff)
 853         {
 854           entry->index += 2;
 855           tab->size += 2;
 856         }
 857       if (tab->first == NULL)
 858         tab->first = entry;
 859       else
 860         tab->last->next = entry;
 861       tab->last = entry;
 862     }
 863
 864   return entry->index;
 865 }
 866
 867 /* Get the number of bytes in a strtab.  */
 868
 869 bfd_size_type
 870 _bfd_stringtab_size (struct bfd_strtab_hash *tab)
 871 {
 872   return tab->size;
 873 }
 874
 875 /* Write out a strtab.  ABFD must already be at the right location in
 876    the file.  */
 877
 878 bfd_boolean
 879 _bfd_stringtab_emit (bfd *abfd, struct bfd_strtab_hash *tab)
 880 {
 881   bfd_boolean xcoff;
 882   struct strtab_hash_entry *entry;
 883
 884   xcoff = tab->xcoff;
 885
 886   for (entry = tab->first; entry != NULL; entry = entry->next)
 887     {
 888       const char *str;
 889       size_t len;
 890
 891       str = entry->root.string;
 892       len = strlen (str) + 1;
 893
 894       if (xcoff)
 895         {
 896           bfd_byte buf[2];
 897
 898           /* The output length includes the null byte.  */
 899           bfd_put_16 (abfd, (bfd_vma) len, buf);
 900           if (bfd_bwrite ((void *) buf, (bfd_size_type) 2, abfd) != 2)
 901             return FALSE;
 902         }
 903
 904       if (bfd_bwrite ((void *) str, (bfd_size_type) len, abfd) != len)
 905         return FALSE;
 906     }
 907
 908   return TRUE;
 909 }