@section Hash Tables
|
@section Hash Tables
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@cindex Hash tables
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@cindex Hash tables
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BFD provides a simple set of hash table functions. Routines
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BFD provides a simple set of hash table functions. Routines
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are provided to initialize a hash table, to free a hash table,
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are provided to initialize a hash table, to free a hash table,
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to look up a string in a hash table and optionally create an
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to look up a string in a hash table and optionally create an
|
entry for it, and to traverse a hash table. There is
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entry for it, and to traverse a hash table. There is
|
currently no routine to delete an string from a hash table.
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currently no routine to delete an string from a hash table.
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|
|
The basic hash table does not permit any data to be stored
|
The basic hash table does not permit any data to be stored
|
with a string. However, a hash table is designed to present a
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with a string. However, a hash table is designed to present a
|
base class from which other types of hash tables may be
|
base class from which other types of hash tables may be
|
derived. These derived types may store additional information
|
derived. These derived types may store additional information
|
with the string. Hash tables were implemented in this way,
|
with the string. Hash tables were implemented in this way,
|
rather than simply providing a data pointer in a hash table
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rather than simply providing a data pointer in a hash table
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entry, because they were designed for use by the linker back
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entry, because they were designed for use by the linker back
|
ends. The linker may create thousands of hash table entries,
|
ends. The linker may create thousands of hash table entries,
|
and the overhead of allocating private data and storing and
|
and the overhead of allocating private data and storing and
|
following pointers becomes noticeable.
|
following pointers becomes noticeable.
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|
|
The basic hash table code is in @code{hash.c}.
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The basic hash table code is in @code{hash.c}.
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|
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@menu
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@menu
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* Creating and Freeing a Hash Table::
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* Creating and Freeing a Hash Table::
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* Looking Up or Entering a String::
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* Looking Up or Entering a String::
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* Traversing a Hash Table::
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* Traversing a Hash Table::
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* Deriving a New Hash Table Type::
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* Deriving a New Hash Table Type::
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@end menu
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@end menu
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|
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@node Creating and Freeing a Hash Table, Looking Up or Entering a String, Hash Tables, Hash Tables
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@node Creating and Freeing a Hash Table, Looking Up or Entering a String, Hash Tables, Hash Tables
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@subsection Creating and freeing a hash table
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@subsection Creating and freeing a hash table
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@findex bfd_hash_table_init
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@findex bfd_hash_table_init
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@findex bfd_hash_table_init_n
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@findex bfd_hash_table_init_n
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To create a hash table, create an instance of a @code{struct
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To create a hash table, create an instance of a @code{struct
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bfd_hash_table} (defined in @code{bfd.h}) and call
|
bfd_hash_table} (defined in @code{bfd.h}) and call
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@code{bfd_hash_table_init} (if you know approximately how many
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@code{bfd_hash_table_init} (if you know approximately how many
|
entries you will need, the function @code{bfd_hash_table_init_n},
|
entries you will need, the function @code{bfd_hash_table_init_n},
|
which takes a @var{size} argument, may be used).
|
which takes a @var{size} argument, may be used).
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@code{bfd_hash_table_init} returns @code{false} if some sort of
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@code{bfd_hash_table_init} returns @code{false} if some sort of
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error occurs.
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error occurs.
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|
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@findex bfd_hash_newfunc
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@findex bfd_hash_newfunc
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The function @code{bfd_hash_table_init} take as an argument a
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The function @code{bfd_hash_table_init} take as an argument a
|
function to use to create new entries. For a basic hash
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function to use to create new entries. For a basic hash
|
table, use the function @code{bfd_hash_newfunc}. @xref{Deriving
|
table, use the function @code{bfd_hash_newfunc}. @xref{Deriving
|
a New Hash Table Type}, for why you would want to use a
|
a New Hash Table Type}, for why you would want to use a
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different value for this argument.
|
different value for this argument.
|
|
|
@findex bfd_hash_allocate
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@findex bfd_hash_allocate
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@code{bfd_hash_table_init} will create an objalloc which will be
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@code{bfd_hash_table_init} will create an objalloc which will be
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used to allocate new entries. You may allocate memory on this
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used to allocate new entries. You may allocate memory on this
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objalloc using @code{bfd_hash_allocate}.
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objalloc using @code{bfd_hash_allocate}.
|
|
|
@findex bfd_hash_table_free
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@findex bfd_hash_table_free
|
Use @code{bfd_hash_table_free} to free up all the memory that has
|
Use @code{bfd_hash_table_free} to free up all the memory that has
|
been allocated for a hash table. This will not free up the
|
been allocated for a hash table. This will not free up the
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@code{struct bfd_hash_table} itself, which you must provide.
|
@code{struct bfd_hash_table} itself, which you must provide.
|
|
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@node Looking Up or Entering a String, Traversing a Hash Table, Creating and Freeing a Hash Table, Hash Tables
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@node Looking Up or Entering a String, Traversing a Hash Table, Creating and Freeing a Hash Table, Hash Tables
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@subsection Looking up or entering a string
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@subsection Looking up or entering a string
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@findex bfd_hash_lookup
|
@findex bfd_hash_lookup
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The function @code{bfd_hash_lookup} is used both to look up a
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The function @code{bfd_hash_lookup} is used both to look up a
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string in the hash table and to create a new entry.
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string in the hash table and to create a new entry.
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|
|
If the @var{create} argument is @code{false}, @code{bfd_hash_lookup}
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If the @var{create} argument is @code{false}, @code{bfd_hash_lookup}
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will look up a string. If the string is found, it will
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will look up a string. If the string is found, it will
|
returns a pointer to a @code{struct bfd_hash_entry}. If the
|
returns a pointer to a @code{struct bfd_hash_entry}. If the
|
string is not found in the table @code{bfd_hash_lookup} will
|
string is not found in the table @code{bfd_hash_lookup} will
|
return @code{NULL}. You should not modify any of the fields in
|
return @code{NULL}. You should not modify any of the fields in
|
the returns @code{struct bfd_hash_entry}.
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the returns @code{struct bfd_hash_entry}.
|
|
|
If the @var{create} argument is @code{true}, the string will be
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If the @var{create} argument is @code{true}, the string will be
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entered into the hash table if it is not already there.
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entered into the hash table if it is not already there.
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Either way a pointer to a @code{struct bfd_hash_entry} will be
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Either way a pointer to a @code{struct bfd_hash_entry} will be
|
returned, either to the existing structure or to a newly
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returned, either to the existing structure or to a newly
|
created one. In this case, a @code{NULL} return means that an
|
created one. In this case, a @code{NULL} return means that an
|
error occurred.
|
error occurred.
|
|
|
If the @var{create} argument is @code{true}, and a new entry is
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If the @var{create} argument is @code{true}, and a new entry is
|
created, the @var{copy} argument is used to decide whether to
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created, the @var{copy} argument is used to decide whether to
|
copy the string onto the hash table objalloc or not. If
|
copy the string onto the hash table objalloc or not. If
|
@var{copy} is passed as @code{false}, you must be careful not to
|
@var{copy} is passed as @code{false}, you must be careful not to
|
deallocate or modify the string as long as the hash table
|
deallocate or modify the string as long as the hash table
|
exists.
|
exists.
|
|
|
@node Traversing a Hash Table, Deriving a New Hash Table Type, Looking Up or Entering a String, Hash Tables
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@node Traversing a Hash Table, Deriving a New Hash Table Type, Looking Up or Entering a String, Hash Tables
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@subsection Traversing a hash table
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@subsection Traversing a hash table
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@findex bfd_hash_traverse
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@findex bfd_hash_traverse
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The function @code{bfd_hash_traverse} may be used to traverse a
|
The function @code{bfd_hash_traverse} may be used to traverse a
|
hash table, calling a function on each element. The traversal
|
hash table, calling a function on each element. The traversal
|
is done in a random order.
|
is done in a random order.
|
|
|
@code{bfd_hash_traverse} takes as arguments a function and a
|
@code{bfd_hash_traverse} takes as arguments a function and a
|
generic @code{void *} pointer. The function is called with a
|
generic @code{void *} pointer. The function is called with a
|
hash table entry (a @code{struct bfd_hash_entry *}) and the
|
hash table entry (a @code{struct bfd_hash_entry *}) and the
|
generic pointer passed to @code{bfd_hash_traverse}. The function
|
generic pointer passed to @code{bfd_hash_traverse}. The function
|
must return a @code{boolean} value, which indicates whether to
|
must return a @code{boolean} value, which indicates whether to
|
continue traversing the hash table. If the function returns
|
continue traversing the hash table. If the function returns
|
@code{false}, @code{bfd_hash_traverse} will stop the traversal and
|
@code{false}, @code{bfd_hash_traverse} will stop the traversal and
|
return immediately.
|
return immediately.
|
|
|
@node Deriving a New Hash Table Type, , Traversing a Hash Table, Hash Tables
|
@node Deriving a New Hash Table Type, , Traversing a Hash Table, Hash Tables
|
@subsection Deriving a new hash table type
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@subsection Deriving a new hash table type
|
Many uses of hash tables want to store additional information
|
Many uses of hash tables want to store additional information
|
which each entry in the hash table. Some also find it
|
which each entry in the hash table. Some also find it
|
convenient to store additional information with the hash table
|
convenient to store additional information with the hash table
|
itself. This may be done using a derived hash table.
|
itself. This may be done using a derived hash table.
|
|
|
Since C is not an object oriented language, creating a derived
|
Since C is not an object oriented language, creating a derived
|
hash table requires sticking together some boilerplate
|
hash table requires sticking together some boilerplate
|
routines with a few differences specific to the type of hash
|
routines with a few differences specific to the type of hash
|
table you want to create.
|
table you want to create.
|
|
|
An example of a derived hash table is the linker hash table.
|
An example of a derived hash table is the linker hash table.
|
The structures for this are defined in @code{bfdlink.h}. The
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The structures for this are defined in @code{bfdlink.h}. The
|
functions are in @code{linker.c}.
|
functions are in @code{linker.c}.
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|
|
You may also derive a hash table from an already derived hash
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You may also derive a hash table from an already derived hash
|
table. For example, the a.out linker backend code uses a hash
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table. For example, the a.out linker backend code uses a hash
|
table derived from the linker hash table.
|
table derived from the linker hash table.
|
|
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@menu
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@menu
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* Define the Derived Structures::
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* Define the Derived Structures::
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* Write the Derived Creation Routine::
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* Write the Derived Creation Routine::
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* Write Other Derived Routines::
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* Write Other Derived Routines::
|
@end menu
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@end menu
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|
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@node Define the Derived Structures, Write the Derived Creation Routine, Deriving a New Hash Table Type, Deriving a New Hash Table Type
|
@node 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
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@subsubsection Define the derived structures
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You must define a structure for an entry in the hash table,
|
You must define a structure for an entry in the hash table,
|
and a structure for the hash table itself.
|
and a structure for the hash table itself.
|
|
|
The first field in the structure for an entry in the hash
|
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
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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
|
you are deriving from. If you are deriving from a basic hash
|
table this is @code{struct bfd_hash_entry}, which is defined in
|
table this is @code{struct bfd_hash_entry}, which is defined in
|
@code{bfd.h}. The first field in the structure for the hash
|
@code{bfd.h}. The first field in the structure for the hash
|
table itself must be of the type of the hash table you are
|
table itself must be of the type of the hash table you are
|
deriving from itself. If you are deriving from a basic hash
|
deriving from itself. If you are deriving from a basic hash
|
table, this is @code{struct bfd_hash_table}.
|
table, this is @code{struct bfd_hash_table}.
|
|
|
For example, the linker hash table defines @code{struct
|
For example, the linker hash table defines @code{struct
|
bfd_link_hash_entry} (in @code{bfdlink.h}). The first field,
|
bfd_link_hash_entry} (in @code{bfdlink.h}). The first field,
|
@code{root}, is of type @code{struct bfd_hash_entry}. Similarly,
|
@code{root}, is of type @code{struct bfd_hash_entry}. Similarly,
|
the first field in @code{struct bfd_link_hash_table}, @code{table},
|
the first field in @code{struct bfd_link_hash_table}, @code{table},
|
is of type @code{struct bfd_hash_table}.
|
is of type @code{struct bfd_hash_table}.
|
|
|
@node Write the Derived Creation Routine, Write Other Derived Routines, Define the Derived Structures, Deriving a New Hash Table Type
|
@node 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
|
@subsubsection Write the derived creation routine
|
You must write a routine which will create and initialize an
|
You must write a routine which will create and initialize an
|
entry in the hash table. This routine is passed as the
|
entry in the hash table. This routine is passed as the
|
function argument to @code{bfd_hash_table_init}.
|
function argument to @code{bfd_hash_table_init}.
|
|
|
In order to permit other hash tables to be derived from the
|
In order to permit other hash tables to be derived from the
|
hash table you are creating, this routine must be written in a
|
hash table you are creating, this routine must be written in a
|
standard way.
|
standard way.
|
|
|
The first argument to the creation routine is a pointer to a
|
The first argument to the creation routine is a pointer to a
|
hash table entry. This may be @code{NULL}, in which case the
|
hash table entry. This may be @code{NULL}, in which case the
|
routine should allocate the right amount of space. Otherwise
|
routine should allocate the right amount of space. Otherwise
|
the space has already been allocated by a hash table type
|
the space has already been allocated by a hash table type
|
derived from this one.
|
derived from this one.
|
|
|
After allocating space, the creation routine must call the
|
After allocating space, the creation routine must call the
|
creation routine of the hash table type it is derived from,
|
creation routine of the hash table type it is derived from,
|
passing in a pointer to the space it just allocated. This
|
passing in a pointer to the space it just allocated. This
|
will initialize any fields used by the base hash table.
|
will initialize any fields used by the base hash table.
|
|
|
Finally the creation routine must initialize any local fields
|
Finally the creation routine must initialize any local fields
|
for the new hash table type.
|
for the new hash table type.
|
|
|
Here is a boilerplate example of a creation routine.
|
Here is a boilerplate example of a creation routine.
|
@var{function_name} is the name of the routine.
|
@var{function_name} is the name of the routine.
|
@var{entry_type} is the type of an entry in the hash table you
|
@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
|
are creating. @var{base_newfunc} is the name of the creation
|
routine of the hash table type your hash table is derived
|
routine of the hash table type your hash table is derived
|
from.
|
from.
|
|
|
|
|
@example
|
@example
|
struct bfd_hash_entry *
|
struct bfd_hash_entry *
|
@var{function_name} (entry, table, string)
|
@var{function_name} (entry, table, string)
|
struct bfd_hash_entry *entry;
|
struct bfd_hash_entry *entry;
|
struct bfd_hash_table *table;
|
struct bfd_hash_table *table;
|
const char *string;
|
const char *string;
|
@{
|
@{
|
struct @var{entry_type} *ret = (@var{entry_type} *) entry;
|
struct @var{entry_type} *ret = (@var{entry_type} *) entry;
|
|
|
/* Allocate the structure if it has not already been allocated by a
|
/* Allocate the structure if it has not already been allocated by a
|
derived class. */
|
derived class. */
|
if (ret == (@var{entry_type} *) NULL)
|
if (ret == (@var{entry_type} *) NULL)
|
@{
|
@{
|
ret = ((@var{entry_type} *)
|
ret = ((@var{entry_type} *)
|
bfd_hash_allocate (table, sizeof (@var{entry_type})));
|
bfd_hash_allocate (table, sizeof (@var{entry_type})));
|
if (ret == (@var{entry_type} *) NULL)
|
if (ret == (@var{entry_type} *) NULL)
|
return NULL;
|
return NULL;
|
@}
|
@}
|
|
|
/* Call the allocation method of the base class. */
|
/* Call the allocation method of the base class. */
|
ret = ((@var{entry_type} *)
|
ret = ((@var{entry_type} *)
|
@var{base_newfunc} ((struct bfd_hash_entry *) ret, table, string));
|
@var{base_newfunc} ((struct bfd_hash_entry *) ret, table, string));
|
|
|
/* Initialize the local fields here. */
|
/* Initialize the local fields here. */
|
|
|
return (struct bfd_hash_entry *) ret;
|
return (struct bfd_hash_entry *) ret;
|
@}
|
@}
|
@end example
|
@end example
|
@strong{Description}@*
|
@strong{Description}@*
|
The creation routine for the linker hash table, which is in
|
The creation routine for the linker hash table, which is in
|
@code{linker.c}, looks just like this example.
|
@code{linker.c}, looks just like this example.
|
@var{function_name} is @code{_bfd_link_hash_newfunc}.
|
@var{function_name} is @code{_bfd_link_hash_newfunc}.
|
@var{entry_type} is @code{struct bfd_link_hash_entry}.
|
@var{entry_type} is @code{struct bfd_link_hash_entry}.
|
@var{base_newfunc} is @code{bfd_hash_newfunc}, the creation
|
@var{base_newfunc} is @code{bfd_hash_newfunc}, the creation
|
routine for a basic hash table.
|
routine for a basic hash table.
|
|
|
@code{_bfd_link_hash_newfunc} also initializes the local fields
|
@code{_bfd_link_hash_newfunc} also initializes the local fields
|
in a linker hash table entry: @code{type}, @code{written} and
|
in a linker hash table entry: @code{type}, @code{written} and
|
@code{next}.
|
@code{next}.
|
|
|
@node Write Other Derived Routines, , Write the Derived Creation Routine, Deriving a New Hash Table Type
|
@node Write Other Derived Routines, , Write the Derived Creation Routine, Deriving a New Hash Table Type
|
@subsubsection Write other derived routines
|
@subsubsection Write other derived routines
|
You will want to write other routines for your new hash table,
|
You will want to write other routines for your new hash table,
|
as well.
|
as well.
|
|
|
You will want an initialization routine which calls the
|
You will want an initialization routine which calls the
|
initialization routine of the hash table you are deriving from
|
initialization routine of the hash table you are deriving from
|
and initializes any other local fields. For the linker hash
|
and initializes any other local fields. For the linker hash
|
table, this is @code{_bfd_link_hash_table_init} in @code{linker.c}.
|
table, this is @code{_bfd_link_hash_table_init} in @code{linker.c}.
|
|
|
You will want a lookup routine which calls the lookup routine
|
You will want a lookup routine which calls the lookup routine
|
of the hash table you are deriving from and casts the result.
|
of the hash table you are deriving from and casts the result.
|
The linker hash table uses @code{bfd_link_hash_lookup} in
|
The linker hash table uses @code{bfd_link_hash_lookup} in
|
@code{linker.c} (this actually takes an additional argument which
|
@code{linker.c} (this actually takes an additional argument which
|
it uses to decide how to return the looked up value).
|
it uses to decide how to return the looked up value).
|
|
|
You may want a traversal routine. This should just call the
|
You may want a traversal routine. This should just call the
|
traversal routine of the hash table you are deriving from with
|
traversal routine of the hash table you are deriving from with
|
appropriate casts. The linker hash table uses
|
appropriate casts. The linker hash table uses
|
@code{bfd_link_hash_traverse} in @code{linker.c}.
|
@code{bfd_link_hash_traverse} in @code{linker.c}.
|
|
|
These routines may simply be defined as macros. For example,
|
These routines may simply be defined as macros. For example,
|
the a.out backend linker hash table, which is derived from the
|
the a.out backend linker hash table, which is derived from the
|
linker hash table, uses macros for the lookup and traversal
|
linker hash table, uses macros for the lookup and traversal
|
routines. These are @code{aout_link_hash_lookup} and
|
routines. These are @code{aout_link_hash_lookup} and
|
@code{aout_link_hash_traverse} in aoutx.h.
|
@code{aout_link_hash_traverse} in aoutx.h.
|
|
|
|
|
