bfd/hash.c

/* hash.c -- hash table routines for BFD
   Copyright (C) 1993-2024 Free Software Foundation, Inc.
   Written by Steve Chamberlain <sac@cygnus.com>

   This file is part of BFD, the Binary File Descriptor library.

   This program 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 3 of the License, or
   (at your option) any later version.

   This program 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 this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
   MA 02110-1301, USA.  */

#include "sysdep.h"
#include "bfd.h"
#include "libbfd.h"
#include "objalloc.h"
#include "libiberty.h"

/*
SECTION
	Hash Tables

@cindex Hash tables
	BFD provides a simple set of hash table functions.  Routines
	are provided to initialize a hash table, to free a hash table,
	to look up a string in a hash table and optionally create an
	entry for it, and to traverse a hash table.  There is
	currently no routine to delete an string from a hash table.

	The basic hash table does not permit any data to be stored
	with a string.  However, a hash table is designed to present a
	base class from which other types of hash tables may be
	derived.  These derived types may store additional information
	with the string.  Hash tables were implemented in this way,
	rather than simply providing a data pointer in a hash table
	entry, because they were designed for use by the linker back
	ends.  The linker may create thousands of hash table entries,
	and the overhead of allocating private data and storing and
	following pointers becomes noticeable.

	The basic hash table code is in <<hash.c>>.

@menu
@* Creating and Freeing a Hash Table::
@* Looking Up or Entering a String::
@* Traversing a Hash Table::
@* Deriving a New Hash Table Type::
@end menu

INODE
Creating and Freeing a Hash Table, Looking Up or Entering a String, Hash Tables, Hash Tables
SUBSECTION
	Creating and freeing a hash table

@findex bfd_hash_table_init
@findex bfd_hash_table_init_n
	To create a hash table, create an instance of a <<struct
	bfd_hash_table>> (defined in <<bfd.h>>) and call
	<<bfd_hash_table_init>> (if you know approximately how many
	entries you will need, the function <<bfd_hash_table_init_n>>,
	which takes a @var{size} argument, may be used).
	<<bfd_hash_table_init>> returns <<FALSE>> if some sort of
	error occurs.

@findex bfd_hash_newfunc
	The function <<bfd_hash_table_init>> take as an argument a
	function to use to create new entries.  For a basic hash
	table, use the function <<bfd_hash_newfunc>>.  @xref{Deriving
	a New Hash Table Type}, for why you would want to use a
	different value for this argument.

@findex bfd_hash_allocate
	<<bfd_hash_table_init>> will create an objalloc which will be
	used to allocate new entries.  You may allocate memory on this
	objalloc using <<bfd_hash_allocate>>.

@findex bfd_hash_table_free
	Use <<bfd_hash_table_free>> to free up all the memory that has
	been allocated for a hash table.  This will not free up the
	<<struct bfd_hash_table>> itself, which you must provide.

@findex bfd_hash_set_default_size
	Use <<bfd_hash_set_default_size>> to set the default size of
	hash table to use.

INODE
Looking Up or Entering a String, Traversing a Hash Table, Creating and Freeing a Hash Table, Hash Tables
SUBSECTION
	Looking up or entering a string

@findex bfd_hash_lookup
	The function <<bfd_hash_lookup>> is used both to look up a
	string in the hash table and to create a new entry.

	If the @var{create} argument is <<FALSE>>, <<bfd_hash_lookup>>
	will look up a string.  If the string is found, it will
	returns a pointer to a <<struct bfd_hash_entry>>.  If the
	string is not found in the table <<bfd_hash_lookup>> will
	return <<NULL>>.  You should not modify any of the fields in
	the returns <<struct bfd_hash_entry>>.

	If the @var{create} argument is <<TRUE>>, the string will be
	entered into the hash table if it is not already there.
	Either way a pointer to a <<struct bfd_hash_entry>> will be
	returned, either to the existing structure or to a newly
	created one.  In this case, a <<NULL>> return means that an
	error occurred.

	If the @var{create} argument is <<TRUE>>, and a new entry is
	created, the @var{copy} argument is used to decide whether to
	copy the string onto the hash table objalloc or not.  If
	@var{copy} is passed as <<FALSE>>, you must be careful not to
	deallocate or modify the string as long as the hash table
	exists.

INODE
Traversing a Hash Table, Deriving a New Hash Table Type, Looking Up or Entering a String, Hash Tables
SUBSECTION
	Traversing a hash table

@findex bfd_hash_traverse
	The function <<bfd_hash_traverse>> may be used to traverse a
	hash table, calling a function on each element.  The traversal
	is done in a random order.

	<<bfd_hash_traverse>> takes as arguments a function and a
	generic <<void *>> pointer.  The function is called with a
	hash table entry (a <<struct bfd_hash_entry *>>) and the
	generic pointer passed to <<bfd_hash_traverse>>.  The function
	must return a <<boolean>> value, which indicates whether to
	continue traversing the hash table.  If the function returns
	<<FALSE>>, <<bfd_hash_traverse>> will stop the traversal and
	return immediately.

INODE
Deriving a New Hash Table Type, , Traversing a Hash Table, Hash Tables
SUBSECTION
	Deriving a new hash table type

	Many uses of hash tables want to store additional information
	which each entry in the hash table.  Some also find it
	convenient to store additional information with the hash table
	itself.  This may be done using a derived hash table.

	Since C is not an object oriented language, creating a derived
	hash table requires sticking together some boilerplate
	routines with a few differences specific to the type of hash
	table you want to create.

	An example of a derived hash table is the linker hash table.
	The structures for this are defined in <<bfdlink.h>>.  The
	functions are in <<linker.c>>.

	You may also derive a hash table from an already derived hash
	table.  For example, the a.out linker backend code uses a hash
	table derived from the linker hash table.

@menu
@* Define the Derived Structures::
@* Write the Derived Creation Routine::
@* Write Other Derived Routines::
@end menu

INODE
Define the Derived Structures, Write the Derived Creation Routine, Deriving a New Hash Table Type, Deriving a New Hash Table Type
SUBSUBSECTION
	Define the derived structures

	You must define a structure for an entry in the hash table,
	and a structure for the hash table itself.

	The first field in the structure for an entry in the hash
	table must be of the type used for an entry in the hash table
	you are deriving from.  If you are deriving from a basic hash
	table this is <<struct bfd_hash_entry>>, which is defined in
	<<bfd.h>>.  The first field in the structure for the hash
	table itself must be of the type of the hash table you are
	deriving from itself.  If you are deriving from a basic hash
	table, this is <<struct bfd_hash_table>>.

	For example, the linker hash table defines <<struct
	bfd_link_hash_entry>> (in <<bfdlink.h>>).  The first field,
	<<root>>, is of type <<struct bfd_hash_entry>>.  Similarly,
	the first field in <<struct bfd_link_hash_table>>, <<table>>,
	is of type <<struct bfd_hash_table>>.

INODE
Write the Derived Creation Routine, Write Other Derived Routines, Define the Derived Structures, Deriving a New Hash Table Type
SUBSUBSECTION
	Write the derived creation routine

	You must write a routine which will create and initialize an
	entry in the hash table.  This routine is passed as the
	function argument to <<bfd_hash_table_init>>.

	In order to permit other hash tables to be derived from the
	hash table you are creating, this routine must be written in a
	standard way.

	The first argument to the creation routine is a pointer to a
	hash table entry.  This may be <<NULL>>, in which case the
	routine should allocate the right amount of space.  Otherwise
	the space has already been allocated by a hash table type
	derived from this one.

	After allocating space, the creation routine must call the
	creation routine of the hash table type it is derived from,
	passing in a pointer to the space it just allocated.  This
	will initialize any fields used by the base hash table.

	Finally the creation routine must initialize any local fields
	for the new hash table type.

	Here is a boilerplate example of a creation routine.
	@var{function_name} is the name of the routine.
	@var{entry_type} is the type of an entry in the hash table you
	are creating.  @var{base_newfunc} is the name of the creation
	routine of the hash table type your hash table is derived
	from.

EXAMPLE

.struct bfd_hash_entry *
.@var{function_name} (struct bfd_hash_entry *entry,
.		      struct bfd_hash_table *table,
.		      const char *string)
.{
.  struct @var{entry_type} *ret = (@var{entry_type} *) entry;
.
. {* Allocate the structure if it has not already been allocated by a
.    derived class.  *}
.  if (ret == NULL)
.    {
.      ret = bfd_hash_allocate (table, sizeof (* ret));
.      if (ret == NULL)
.	 return NULL;
.    }
.
. {* Call the allocation method of the base class.  *}
.  ret = ((@var{entry_type} *)
.	  @var{base_newfunc} ((struct bfd_hash_entry *) ret, table, string));
.
. {* Initialize the local fields here.  *}
.
.  return (struct bfd_hash_entry *) ret;
.}

DESCRIPTION
	The creation routine for the linker hash table, which is in
	<<linker.c>>, looks just like this example.
	@var{function_name} is <<_bfd_link_hash_newfunc>>.
	@var{entry_type} is <<struct bfd_link_hash_entry>>.
	@var{base_newfunc} is <<bfd_hash_newfunc>>, the creation
	routine for a basic hash table.

	<<_bfd_link_hash_newfunc>> also initializes the local fields
	in a linker hash table entry: <<type>>, <<written>> and
	<<next>>.

INODE
Write Other Derived Routines, , Write the Derived Creation Routine, Deriving a New Hash Table Type
SUBSUBSECTION
	Write other derived routines

	You will want to write other routines for your new hash table,
	as well.

	You will want an initialization routine which calls the
	initialization routine of the hash table you are deriving from
	and initializes any other local fields.  For the linker hash
	table, this is <<_bfd_link_hash_table_init>> in <<linker.c>>.

	You will want a lookup routine which calls the lookup routine
	of the hash table you are deriving from and casts the result.
	The linker hash table uses <<bfd_link_hash_lookup>> in
	<<linker.c>> (this actually takes an additional argument which
	it uses to decide how to return the looked up value).

	You may want a traversal routine.  This should just call the
	traversal routine of the hash table you are deriving from with
	appropriate casts.  The linker hash table uses
	<<bfd_link_hash_traverse>> in <<linker.c>>.

	These routines may simply be defined as macros.  For example,
	the a.out backend linker hash table, which is derived from the
	linker hash table, uses macros for the lookup and traversal
	routines.  These are <<aout_link_hash_lookup>> and
	<<aout_link_hash_traverse>> in aoutx.h.

EXTERNAL
.{* An element in the hash table.  Most uses will actually use a larger
.   structure, and an instance of this will be the first field.  *}
.
.struct bfd_hash_entry
.{
.  {* Next entry for this hash code.  *}
.  struct bfd_hash_entry *next;
.  {* String being hashed.  *}
.  const char *string;
.  {* Hash code.  This is the full hash code, not the index into the
.     table.  *}
.  unsigned long hash;
.};
.
.{* A hash table.  *}
.
.struct bfd_hash_table
.{
.  {* The hash array.  *}
.  struct bfd_hash_entry **table;
.  {* A function used to create new elements in the hash table.  The
.     first entry is itself a pointer to an element.  When this
.     function is first invoked, this pointer will be NULL.  However,
.     having the pointer permits a hierarchy of method functions to be
.     built each of which calls the function in the superclass.  Thus
.     each function should be written to allocate a new block of memory
.     only if the argument is NULL.  *}
.  struct bfd_hash_entry *(*newfunc)
.    (struct bfd_hash_entry *, struct bfd_hash_table *, const char *);
.  {* An objalloc for this hash table.  This is a struct objalloc *,
.     but we use void * to avoid requiring the inclusion of objalloc.h.  *}
.  void *memory;
.  {* The number of slots in the hash table.  *}
.  unsigned int size;
.  {* The number of entries in the hash table.  *}
.  unsigned int count;
.  {* The size of elements.  *}
.  unsigned int entsize;
.  {* If non-zero, don't grow the hash table.  *}
.  unsigned int frozen:1;
.};
.
*/

/* The default number of entries to use when creating a hash table.  */
#define DEFAULT_SIZE 4051

/* The following function returns a nearest prime number which is
   greater than N, and near a power of two.  Copied from libiberty.
   Returns zero for ridiculously large N to signify an error.  */

static uint32_t
higher_prime_number (uint32_t n)
{
  /* These are primes that are near, but slightly smaller than, a
     power of two.  */
  static const uint32_t primes[] =
    {
      UINT32_C (31),
      UINT32_C (61),
      UINT32_C (127),
      UINT32_C (251),
      UINT32_C (509),
      UINT32_C (1021),
      UINT32_C (2039),
      UINT32_C (4093),
      UINT32_C (8191),
      UINT32_C (16381),
      UINT32_C (32749),
      UINT32_C (65521),
      UINT32_C (131071),
      UINT32_C (262139),
      UINT32_C (524287),
      UINT32_C (1048573),
      UINT32_C (2097143),
      UINT32_C (4194301),
      UINT32_C (8388593),
      UINT32_C (16777213),
      UINT32_C (33554393),
      UINT32_C (67108859),
      UINT32_C (134217689),
      UINT32_C (268435399),
      UINT32_C (536870909),
      UINT32_C (1073741789),
      UINT32_C (2147483647),
      UINT32_C (4294967291)
  };

  const uint32_t *low = &primes[0];
  const uint32_t *high = &primes[sizeof (primes) / sizeof (primes[0])];

  while (low != high)
    {
      const uint32_t *mid = low + (high - low) / 2;
      if (n >= *mid)
	low = mid + 1;
      else
	high = mid;
    }

  if (n >= *low)
    return 0;

  return *low;
}

static unsigned int bfd_default_hash_table_size = DEFAULT_SIZE;

/*
FUNCTION
	bfd_hash_table_init_n

SYNOPSIS
	bool bfd_hash_table_init_n
	  (struct bfd_hash_table *,
	   struct bfd_hash_entry *(* {*newfunc*})
	     (struct bfd_hash_entry *, struct bfd_hash_table *, const char *),
	   unsigned int {*entsize*}, unsigned int {*size*});

DESCRIPTION
	Create a new hash table, given a number of entries.
*/

bool
bfd_hash_table_init_n (struct bfd_hash_table *table,
		       struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
							  struct bfd_hash_table *,
							  const char *),
		       unsigned int entsize,
		       unsigned int size)
{
  unsigned long alloc;

  alloc = size;
  alloc *= sizeof (struct bfd_hash_entry *);
  if (alloc / sizeof (struct bfd_hash_entry *) != size)
    {
      bfd_set_error (bfd_error_no_memory);
      return false;
    }

  table->memory = (void *) objalloc_create ();
  if (table->memory == NULL)
    {
      bfd_set_error (bfd_error_no_memory);
      return false;
    }
  table->table = (struct bfd_hash_entry **)
      objalloc_alloc ((struct objalloc *) table->memory, alloc);
  if (table->table == NULL)
    {
      bfd_hash_table_free (table);
      bfd_set_error (bfd_error_no_memory);
      return false;
    }
  memset ((void *) table->table, 0, alloc);
  table->size = size;
  table->entsize = entsize;
  table->count = 0;
  table->frozen = 0;
  table->newfunc = newfunc;
  return true;
}

/*
FUNCTION
	bfd_hash_table_init

SYNOPSIS
	bool bfd_hash_table_init
	  (struct bfd_hash_table *,
	   struct bfd_hash_entry *(* {*newfunc*})
	     (struct bfd_hash_entry *, struct bfd_hash_table *, const char *),
	   unsigned int {*entsize*});

DESCRIPTION
	Create a new hash table with the default number of entries.
*/

bool
bfd_hash_table_init (struct bfd_hash_table *table,
		     struct bfd_hash_entry *(*newfunc) (struct bfd_hash_entry *,
							struct bfd_hash_table *,
							const char *),
		     unsigned int entsize)
{
  return bfd_hash_table_init_n (table, newfunc, entsize,
				bfd_default_hash_table_size);
}

/*
FUNCTION
	bfd_hash_table_free

SYNOPSIS
	void bfd_hash_table_free (struct bfd_hash_table *);

DESCRIPTION
	Free a hash table.
*/

void
bfd_hash_table_free (struct bfd_hash_table *table)
{
  objalloc_free ((struct objalloc *) table->memory);
  table->memory = NULL;
}

static inline unsigned long
bfd_hash_hash (const char *string, unsigned int *lenp)
{
  const unsigned char *s;
  unsigned long hash;
  unsigned int len;
  unsigned int c;

  BFD_ASSERT (string != NULL);
  hash = 0;
  len = 0;
  s = (const unsigned char *) string;
  while ((c = *s++) != '\0')
    {
      hash += c + (c << 17);
      hash ^= hash >> 2;
    }
  len = (s - (const unsigned char *) string) - 1;
  hash += len + (len << 17);
  hash ^= hash >> 2;
  if (lenp != NULL)
    *lenp = len;
  return hash;
}

/*
FUNCTION
	bfd_hash_lookup

SYNOPSIS
	struct bfd_hash_entry *bfd_hash_lookup
	  (struct bfd_hash_table *, const char *,
	   bool {*create*}, bool {*copy*});

DESCRIPTION
	Look up a string in a hash table.
*/

struct bfd_hash_entry *
bfd_hash_lookup (struct bfd_hash_table *table,
		 const char *string,
		 bool create,
		 bool copy)
{
  unsigned long hash;
  struct bfd_hash_entry *hashp;
  unsigned int len;
  unsigned int _index;

  hash = bfd_hash_hash (string, &len);
  _index = hash % table->size;
  for (hashp = table->table[_index];
       hashp != NULL;
       hashp = hashp->next)
    {
      if (hashp->hash == hash
	  && strcmp (hashp->string, string) == 0)
	return hashp;
    }

  if (! create)
    return NULL;

  if (copy)
    {
      char *new_string;

      new_string = (char *) objalloc_alloc ((struct objalloc *) table->memory,
					    len + 1);
      if (!new_string)
	{
	  bfd_set_error (bfd_error_no_memory);
	  return NULL;
	}
      memcpy (new_string, string, len + 1);
      string = new_string;
    }

  return bfd_hash_insert (table, string, hash);
}

/*
FUNCTION
	bfd_hash_insert

SYNOPSIS
	struct bfd_hash_entry *bfd_hash_insert
	  (struct bfd_hash_table *,
	   const char *,
	   unsigned long {*hash*});

DESCRIPTION
	Insert an entry in a hash table.
*/

struct bfd_hash_entry *
bfd_hash_insert (struct bfd_hash_table *table,
		 const char *string,
		 unsigned long hash)
{
  struct bfd_hash_entry *hashp;
  unsigned int _index;

  hashp = (*table->newfunc) (NULL, table, string);
  if (hashp == NULL)
    return NULL;
  hashp->string = string;
  hashp->hash = hash;
  _index = hash % table->size;
  hashp->next = table->table[_index];
  table->table[_index] = hashp;
  table->count++;

  if (!table->frozen && table->count > table->size * 3 / 4)
    {
      unsigned long newsize = higher_prime_number (table->size);
      struct bfd_hash_entry **newtable;
      unsigned int hi;
      unsigned long alloc = newsize * sizeof (struct bfd_hash_entry *);

      /* If we can't find a higher prime, or we can't possibly alloc
	 that much memory, don't try to grow the table.  */
      if (newsize == 0 || alloc / sizeof (struct bfd_hash_entry *) != newsize)
	{
	  table->frozen = 1;
	  return hashp;
	}

      newtable = ((struct bfd_hash_entry **)
		  objalloc_alloc ((struct objalloc *) table->memory, alloc));
      if (newtable == NULL)
	{
	  table->frozen = 1;
	  return hashp;
	}
      memset (newtable, 0, alloc);

      for (hi = 0; hi < table->size; hi ++)
	while (table->table[hi])
	  {
	    struct bfd_hash_entry *chain = table->table[hi];
	    struct bfd_hash_entry *chain_end = chain;

	    while (chain_end->next && chain_end->next->hash == chain->hash)
	      chain_end = chain_end->next;

	    table->table[hi] = chain_end->next;
	    _index = chain->hash % newsize;
	    chain_end->next = newtable[_index];
	    newtable[_index] = chain;
	  }
      table->table = newtable;
      table->size = newsize;
    }

  return hashp;
}

/*
FUNCTION
	bfd_hash_rename

SYNOPSIS
	void bfd_hash_rename (struct bfd_hash_table *,
			      const char *,
			      struct bfd_hash_entry *);

DESCRIPTION
	Rename an entry in a hash table.
*/

void
bfd_hash_rename (struct bfd_hash_table *table,
		 const char *string,
		 struct bfd_hash_entry *ent)
{
  unsigned int _index;
  struct bfd_hash_entry **pph;

  _index = ent->hash % table->size;
  for (pph = &table->table[_index]; *pph != NULL; pph = &(*pph)->next)
    if (*pph == ent)
      break;
  if (*pph == NULL)
    abort ();

  *pph = ent->next;
  ent->string = string;
  ent->hash = bfd_hash_hash (string, NULL);
  _index = ent->hash % table->size;
  ent->next = table->table[_index];
  table->table[_index] = ent;
}

/*
FUNCTION
	bfd_hash_replace

SYNOPSIS
	void bfd_hash_replace (struct bfd_hash_table *,
			       struct bfd_hash_entry * {*old*},
			       struct bfd_hash_entry * {*new*});

DESCRIPTION
	Replace an entry in a hash table.
*/

void
bfd_hash_replace (struct bfd_hash_table *table,
		  struct bfd_hash_entry *old,
		  struct bfd_hash_entry *nw)
{
  unsigned int _index;
  struct bfd_hash_entry **pph;

  _index = old->hash % table->size;
  for (pph = &table->table[_index];
       (*pph) != NULL;
       pph = &(*pph)->next)
    {
      if (*pph == old)
	{
	  *pph = nw;
	  return;
	}
    }

  abort ();
}

/*
FUNCTION
	bfd_hash_allocate

SYNOPSIS
	void *bfd_hash_allocate (struct bfd_hash_table *,
				 unsigned int {*size*});

DESCRIPTION
	Allocate space in a hash table.
*/

void *
bfd_hash_allocate (struct bfd_hash_table *table,
		   unsigned int size)
{
  void * ret;

  ret = objalloc_alloc ((struct objalloc *) table->memory, size);
  if (ret == NULL && size != 0)
    bfd_set_error (bfd_error_no_memory);
  return ret;
}

/*
FUNCTION
	bfd_hash_newfunc

SYNOPSIS
	struct bfd_hash_entry *bfd_hash_newfunc
	  (struct bfd_hash_entry *,
	   struct bfd_hash_table *,
	   const char *);

DESCRIPTION
	Base method for creating a new hash table entry.
*/

struct bfd_hash_entry *
bfd_hash_newfunc (struct bfd_hash_entry *entry,
		  struct bfd_hash_table *table,
		  const char *string ATTRIBUTE_UNUSED)
{
  if (entry == NULL)
    entry = (struct bfd_hash_entry *) bfd_hash_allocate (table,
							 sizeof (* entry));
  return entry;
}

/*
FUNCTION
	bfd_hash_traverse

SYNOPSIS
	void bfd_hash_traverse
	  (struct bfd_hash_table *,
	   bool (*) (struct bfd_hash_entry *, void *),
	   void *);

DESCRIPTION
	Traverse a hash table.
*/

void
bfd_hash_traverse (struct bfd_hash_table *table,
		   bool (*func) (struct bfd_hash_entry *, void *),
		   void *info)
{
  unsigned int i;

  table->frozen = 1;
  for (i = 0; i < table->size; i++)
    {
      struct bfd_hash_entry *p;

      for (p = table->table[i]; p != NULL; p = p->next)
	if (! (*func) (p, info))
	  goto out;
    }
 out:
  table->frozen = 0;
}

/*
FUNCTION
	bfd_hash_set_default_size

SYNOPSIS
	unsigned int bfd_hash_set_default_size (unsigned int);

DESCRIPTION
	Set hash table default size.
*/

unsigned int
bfd_hash_set_default_size (unsigned int hash_size)
{
  /* These silly_size values result in around 1G and 32M of memory
     being allocated for the table of pointers.  Note that the number
     of elements allocated will be almost twice the size of any power
     of two chosen here.  */
  unsigned int silly_size = sizeof (size_t) > 4 ? 0x4000000 : 0x400000;
  if (hash_size > silly_size)
    hash_size = silly_size;
  else if (hash_size != 0)
    hash_size--;
  hash_size = higher_prime_number (hash_size);
  BFD_ASSERT (hash_size != 0);
  bfd_default_hash_table_size = hash_size;
  return bfd_default_hash_table_size;
}

/* A few different object file formats (a.out, COFF, ELF) use a string
   table.  These functions support adding strings to a string table,
   returning the byte offset, and writing out the table.

   Possible improvements:
   + look for strings matching trailing substrings of other strings
   + better data structures?  balanced trees?
   + look at reducing memory use elsewhere -- maybe if we didn't have
     to construct the entire symbol table at once, we could get by
     with smaller amounts of VM?  (What effect does that have on the
     string table reductions?)  */

/* An entry in the strtab hash table.  */

struct strtab_hash_entry
{
  struct bfd_hash_entry root;
  /* Index in string table.  */
  bfd_size_type index;
  /* Next string in strtab.  */
  struct strtab_hash_entry *next;
};

/* The strtab hash table.  */

struct bfd_strtab_hash
{
  struct bfd_hash_table table;
  /* Size of strtab--also next available index.  */
  bfd_size_type size;
  /* First string in strtab.  */
  struct strtab_hash_entry *first;
  /* Last string in strtab.  */
  struct strtab_hash_entry *last;
  /* Whether to precede strings with a two or four byte length,
     as in the XCOFF .debug section.  */
  char length_field_size;
};


/* Routine to create an entry in a strtab.  */

static struct bfd_hash_entry *
strtab_hash_newfunc (struct bfd_hash_entry *entry,
		     struct bfd_hash_table *table,
		     const char *string)
{
  struct strtab_hash_entry *ret = (struct strtab_hash_entry *) entry;

  /* Allocate the structure if it has not already been allocated by a
     subclass.  */
  if (ret == NULL)
    ret = (struct strtab_hash_entry *) bfd_hash_allocate (table,
							  sizeof (* ret));
  if (ret == NULL)
    return NULL;

  /* Call the allocation method of the superclass.  */
  ret = (struct strtab_hash_entry *)
	 bfd_hash_newfunc ((struct bfd_hash_entry *) ret, table, string);

  if (ret)
    {
      /* Initialize the local fields.  */
      ret->index = (bfd_size_type) -1;
      ret->next = NULL;
    }

  return (struct bfd_hash_entry *) ret;
}

/* Look up an entry in an strtab.  */

#define strtab_hash_lookup(t, string, create, copy) \
  ((struct strtab_hash_entry *) \
   bfd_hash_lookup (&(t)->table, (string), (create), (copy)))

/*
INTERNAL_FUNCTION
	_bfd_stringtab_init

SYNOPSIS
	struct bfd_strtab_hash *_bfd_stringtab_init (void);

DESCRIPTION
	Create a new strtab.
*/

struct bfd_strtab_hash *
_bfd_stringtab_init (void)
{
  struct bfd_strtab_hash *table;
  size_t amt = sizeof (* table);

  table = (struct bfd_strtab_hash *) bfd_malloc (amt);
  if (table == NULL)
    return NULL;

  if (!bfd_hash_table_init (&table->table, strtab_hash_newfunc,
			    sizeof (struct strtab_hash_entry)))
    {
      free (table);
      return NULL;
    }

  table->size = 0;
  table->first = NULL;
  table->last = NULL;
  table->length_field_size = 0;

  return table;
}

/*
INTERNAL_FUNCTION
	_bfd_xcoff_stringtab_init

SYNOPSIS
	struct bfd_strtab_hash *_bfd_xcoff_stringtab_init
	  (bool {*isxcoff64*});

DESCRIPTION
	Create a new strtab in which the strings are output in the format
	used in the XCOFF .debug section: a two byte length precedes each
	string.
*/

struct bfd_strtab_hash *
_bfd_xcoff_stringtab_init (bool isxcoff64)
{
  struct bfd_strtab_hash *ret;

  ret = _bfd_stringtab_init ();
  if (ret != NULL)
    ret->length_field_size = isxcoff64 ? 4 : 2;
  return ret;
}

/*
INTERNAL_FUNCTION
	_bfd_stringtab_free

SYNOPSIS
	void _bfd_stringtab_free (struct bfd_strtab_hash *);

DESCRIPTION
	Free a strtab.
*/

void
_bfd_stringtab_free (struct bfd_strtab_hash *table)
{
  bfd_hash_table_free (&table->table);
  free (table);
}

/*
INTERNAL_FUNCTION
	_bfd_stringtab_add

SYNOPSIS
	bfd_size_type _bfd_stringtab_add
	  (struct bfd_strtab_hash *, const char *,
	   bool {*hash*}, bool {*copy*});

DESCRIPTION
	Get the index of a string in a strtab, adding it if it is not
	already present.  If HASH is FALSE, we don't really use the hash
	table, and we don't eliminate duplicate strings.  If COPY is true
	then store a copy of STR if creating a new entry.
*/

bfd_size_type
_bfd_stringtab_add (struct bfd_strtab_hash *tab,
		    const char *str,
		    bool hash,
		    bool copy)
{
  struct strtab_hash_entry *entry;

  if (hash)
    {
      entry = strtab_hash_lookup (tab, str, true, copy);
      if (entry == NULL)
	return (bfd_size_type) -1;
    }
  else
    {
      entry = (struct strtab_hash_entry *) bfd_hash_allocate (&tab->table,
							      sizeof (* entry));
      if (entry == NULL)
	return (bfd_size_type) -1;
      if (! copy)
	entry->root.string = str;
      else
	{
	  size_t len = strlen (str) + 1;
	  char *n;

	  n = (char *) bfd_hash_allocate (&tab->table, len);
	  if (n == NULL)
	    return (bfd_size_type) -1;
	  memcpy (n, str, len);
	  entry->root.string = n;
	}
      entry->index = (bfd_size_type) -1;
      entry->next = NULL;
    }

  if (entry->index == (bfd_size_type) -1)
    {
      entry->index = tab->size;
      tab->size += strlen (str) + 1;
      entry->index += tab->length_field_size;
      tab->size += tab->length_field_size;
      if (tab->first == NULL)
	tab->first = entry;
      else
	tab->last->next = entry;
      tab->last = entry;
    }

  return entry->index;
}

/*
INTERNAL_FUNCTION
	_bfd_stringtab_size

SYNOPSIS
	bfd_size_type _bfd_stringtab_size (struct bfd_strtab_hash *);

DESCRIPTION
	Get the number of bytes in a strtab.
*/

bfd_size_type
_bfd_stringtab_size (struct bfd_strtab_hash *tab)
{
  return tab->size;
}

/*
INTERNAL_FUNCTION
	_bfd_stringtab_emit

SYNOPSIS
	bool _bfd_stringtab_emit (bfd *, struct bfd_strtab_hash *);

DESCRIPTION
	Write out a strtab.  ABFD must already be at the right location in
	the file.
*/

bool
_bfd_stringtab_emit (bfd *abfd, struct bfd_strtab_hash *tab)
{
  struct strtab_hash_entry *entry;

  for (entry = tab->first; entry != NULL; entry = entry->next)
    {
      const char *str;
      size_t len;

      str = entry->root.string;
      len = strlen (str) + 1;

      if (tab->length_field_size == 4)
	{
	  bfd_byte buf[4];

	  /* The output length includes the null byte.  */
	  bfd_put_32 (abfd, len, buf);
	  if (bfd_write (buf, 4, abfd) != 4)
	    return false;
	}
      else if (tab->length_field_size == 2)
	{
	  bfd_byte buf[2];

	  /* The output length includes the null byte.  */
	  bfd_put_16 (abfd, len, buf);
	  if (bfd_write (buf, 2, abfd) != 2)
	    return false;
	}

      if (bfd_write (str, len, abfd) != len)
	return false;
    }

  return true;
}