2001-01-03 Philip Blundell <pb@futuretv.com>

[binutils.git] / bfd / hash.c

/* hash.c -- hash table routines for BFD
   Copyright (C) 1993, 94, 95, 97, 1999 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 2 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

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

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} (entry, table, string)
.     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 == (@var{entry_type} *) NULL)
.    {
.      ret = ((@var{entry_type} *)
.             bfd_hash_allocate (table, sizeof (@var{entry_type})));
.      if (ret == (@var{entry_type} *) 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.
*/

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

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

boolean
bfd_hash_table_init_n (table, newfunc, size)
     struct bfd_hash_table *table;
     struct bfd_hash_entry *(*newfunc) PARAMS ((struct bfd_hash_entry *,
                                                struct bfd_hash_table *,
                                                const char *));
     unsigned int size;
{
  unsigned int alloc;

  alloc = size * sizeof (struct bfd_hash_entry *);

  table->memory = (PTR) 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_set_error (bfd_error_no_memory);
      return false;
    }
  memset ((PTR) table->table, 0, alloc);
  table->size = size;
  table->newfunc = newfunc;
  return true;
}

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

boolean
bfd_hash_table_init (table, newfunc)
     struct bfd_hash_table *table;
     struct bfd_hash_entry *(*newfunc) PARAMS ((struct bfd_hash_entry *,
                                                struct bfd_hash_table *,
                                                const char *));
{
  return bfd_hash_table_init_n (table, newfunc, DEFAULT_SIZE);
}

/* Free a hash table.  */

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

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

struct bfd_hash_entry *
bfd_hash_lookup (table, string, create, copy)
     struct bfd_hash_table *table;
     const char *string;
     boolean create;
     boolean copy;
{
  register const unsigned char *s;
  register unsigned long hash;
  register unsigned int c;
  struct bfd_hash_entry *hashp;
  unsigned int len;
  unsigned int index;
  
  hash = 0;
  len = 0;
  s = (const unsigned char *) string;
  while ((c = *s++) != '\0')
    {
      hash += c + (c << 17);
      hash ^= hash >> 2;
      ++len;
    }
  hash += len + (len << 17);
  hash ^= hash >> 2;

  index = hash % table->size;
  for (hashp = table->table[index];
       hashp != (struct bfd_hash_entry *) NULL;
       hashp = hashp->next)
    {
      if (hashp->hash == hash
          && strcmp (hashp->string, string) == 0)
        return hashp;
    }

  if (! create)
    return (struct bfd_hash_entry *) NULL;

  hashp = (*table->newfunc) ((struct bfd_hash_entry *) NULL, table, string);
  if (hashp == (struct bfd_hash_entry *) NULL)
    return (struct bfd_hash_entry *) NULL;
  if (copy)
    {
      char *new;

      new = (char *) objalloc_alloc ((struct objalloc *) table->memory,
                                     len + 1);
      if (!new)
        {
          bfd_set_error (bfd_error_no_memory);
          return (struct bfd_hash_entry *) NULL;
        }
      strcpy (new, string);
      string = new;
    }
  hashp->string = string;
  hashp->hash = hash;
  hashp->next = table->table[index];
  table->table[index] = hashp;

  return hashp;
}

/* Replace an entry in a hash table.  */

void
bfd_hash_replace (table, old, nw)
     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) != (struct bfd_hash_entry *) NULL;
       pph = &(*pph)->next)
    {
      if (*pph == old)
        {
          *pph = nw;
          return;
        }
    }

  abort ();
}

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

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

/* Allocate space in a hash table.  */

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

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

/* Traverse a hash table.  */

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

  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))
            return;
        }
    }
}
\f
/* 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 byte length, as in the
     XCOFF .debug section.  */
  boolean xcoff;
};

static struct bfd_hash_entry *strtab_hash_newfunc
  PARAMS ((struct bfd_hash_entry *, struct bfd_hash_table *, const char *));

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

static struct bfd_hash_entry *
strtab_hash_newfunc (entry, table, string)
     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 == (struct strtab_hash_entry *) NULL)
    ret = ((struct strtab_hash_entry *)
           bfd_hash_allocate (table, sizeof (struct strtab_hash_entry)));
  if (ret == (struct strtab_hash_entry *) 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)))

/* Create a new strtab.  */

struct bfd_strtab_hash *
_bfd_stringtab_init ()
{
  struct bfd_strtab_hash *table;

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

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

  table->size = 0;
  table->first = NULL;
  table->last = NULL;
  table->xcoff = false;

  return table;
}

/* 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 ()
{
  struct bfd_strtab_hash *ret;

  ret = _bfd_stringtab_init ();
  if (ret != NULL)
    ret->xcoff = true;
  return ret;
}

/* Free a strtab.  */

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

/* 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.  */

bfd_size_type
_bfd_stringtab_add (tab, str, hash, copy)
     struct bfd_strtab_hash *tab;
     const char *str;
     boolean hash;
     boolean copy;
{
  register 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 (struct strtab_hash_entry)));
      if (entry == NULL)
        return (bfd_size_type) -1;
      if (! copy)
        entry->root.string = str;
      else
        {
          char *n;

          n = (char *) bfd_hash_allocate (&tab->table, strlen (str) + 1);
          if (n == NULL)
            return (bfd_size_type) -1;
          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;
      if (tab->xcoff)
        {
          entry->index += 2;
          tab->size += 2;
        }
      if (tab->first == NULL)
        tab->first = entry;
      else
        tab->last->next = entry;
      tab->last = entry;
    }

  return entry->index;
}

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

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

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

boolean
_bfd_stringtab_emit (abfd, tab)
     register bfd *abfd;
     struct bfd_strtab_hash *tab;
{
  register boolean xcoff;
  register struct strtab_hash_entry *entry;

  xcoff = tab->xcoff;

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

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

      if (xcoff)
        {
          bfd_byte buf[2];

          /* The output length includes the null byte.  */
          bfd_put_16 (abfd, len, buf);
          if (bfd_write ((PTR) buf, 1, 2, abfd) != 2)
            return false;
        }

      if (bfd_write ((PTR) str, 1, len, abfd) != len)
        return false;
    }

  return true;
}