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diff --git a/bfd/doc/hash.texi b/bfd/doc/hash.texi deleted file mode 100644 index 88d9585cc405..000000000000 --- a/bfd/doc/hash.texi +++ /dev/null @@ -1,247 +0,0 @@ -@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 @code{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 - -@node 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 @code{struct -bfd_hash_table} (defined in @code{bfd.h}) and call -@code{bfd_hash_table_init} (if you know approximately how many -entries you will need, the function @code{bfd_hash_table_init_n}, -which takes a @var{size} argument, may be used). -@code{bfd_hash_table_init} returns @code{FALSE} if some sort of -error occurs. - -@findex bfd_hash_newfunc -The function @code{bfd_hash_table_init} take as an argument a -function to use to create new entries. For a basic hash -table, use the function @code{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 -@code{bfd_hash_table_init} will create an objalloc which will be -used to allocate new entries. You may allocate memory on this -objalloc using @code{bfd_hash_allocate}. - -@findex bfd_hash_table_free -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 -@code{struct bfd_hash_table} itself, which you must provide. - -@findex bfd_hash_set_default_size -Use @code{bfd_hash_set_default_size} to set the default size of -hash table to use. - -@node 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 @code{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 @code{FALSE}, @code{bfd_hash_lookup} -will look up a string. If the string is found, it will -returns a pointer to a @code{struct bfd_hash_entry}. If the -string is not found in the table @code{bfd_hash_lookup} will -return @code{NULL}. You should not modify any of the fields in -the returns @code{struct bfd_hash_entry}. - -If the @var{create} argument is @code{TRUE}, the string will be -entered into the hash table if it is not already there. -Either way a pointer to a @code{struct bfd_hash_entry} will be -returned, either to the existing structure or to a newly -created one. In this case, a @code{NULL} return means that an -error occurred. - -If the @var{create} argument is @code{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 @code{FALSE}, you must be careful not to -deallocate or modify the string as long as the hash table -exists. - -@node 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 @code{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. - -@code{bfd_hash_traverse} takes as arguments a function and a -generic @code{void *} pointer. The function is called with a -hash table entry (a @code{struct bfd_hash_entry *}) and the -generic pointer passed to @code{bfd_hash_traverse}. The function -must return a @code{boolean} value, which indicates whether to -continue traversing the hash table. If the function returns -@code{FALSE}, @code{bfd_hash_traverse} will stop the traversal and -return immediately. - -@node 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 @code{bfdlink.h}. The -functions are in @code{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 - -@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 -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 @code{struct bfd_hash_entry}, which is defined in -@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 -deriving from itself. If you are deriving from a basic hash -table, this is @code{struct bfd_hash_table}. - -For example, the linker hash table defines @code{struct -bfd_link_hash_entry} (in @code{bfdlink.h}). The first field, -@code{root}, is of type @code{struct bfd_hash_entry}. Similarly, -the first field in @code{struct bfd_link_hash_table}, @code{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 -@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 @code{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 @code{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; -@} -@end example -@strong{Description}@* -The creation routine for the linker hash table, which is in -@code{linker.c}, looks just like this example. -@var{function_name} is @code{_bfd_link_hash_newfunc}. -@var{entry_type} is @code{struct bfd_link_hash_entry}. -@var{base_newfunc} is @code{bfd_hash_newfunc}, the creation -routine for a basic hash table. - -@code{_bfd_link_hash_newfunc} also initializes the local fields -in a linker hash table entry: @code{type}, @code{written} and -@code{next}. - -@node 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 @code{_bfd_link_hash_table_init} in @code{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 @code{bfd_link_hash_lookup} in -@code{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 -@code{bfd_link_hash_traverse} in @code{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 @code{aout_link_hash_lookup} and -@code{aout_link_hash_traverse} in aoutx.h. - |