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+/* hash.c -- hash table routines for BFD
+   Copyright (C) 1993, 94 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+#include "bfd.h"
+#include "sysdep.h"
+#include "libbfd.h"
+#include "obstack.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 obstack which will be
+	used to allocate new entries.  You may allocate memory on this
+	obstack 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 obstack 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.
+*/
+
+/* Obstack allocation and deallocation routines.  */
+#define obstack_chunk_alloc malloc
+#define obstack_chunk_free free
+
+/* 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 *);
+  if (!obstack_begin (&table->memory, alloc))
+    {
+      bfd_set_error (bfd_error_no_memory);
+      return false;
+    }
+  table->table = ((struct bfd_hash_entry **)
+		  obstack_alloc (&table->memory, alloc));
+  if (!table->table)
+    {
+      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;
+{
+  obstack_free (&table->memory, (PTR) 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 *) obstack_alloc (&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;
+}
+
+/* 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;
+{
+  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 = obstack_alloc (&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;
+	}
+    }
+}