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openssl/doc/crypto/lhash.pod

 =pod
 
 =head1 NAME
 
 lh_new, lh_free, lh_insert, lh_delete, lh_retrieve, lh_doall, lh_doall_arg, lh_error - dynamic hash table
 
 =head1 SYNOPSIS
 
  #include <openssl/lhash.h>
 
- LHASH *lh_new(LHASH_HASH_FN_TYPE hash, LHASH_COMP_FN_TYPE compare);
- void lh_free(LHASH *table);
+ DECLARE_LHASH_OF(<type>);
 
- void *lh_insert(LHASH *table, void *data);
- void *lh_delete(LHASH *table, void *data);
- void *lh_retrieve(LHASH *table, void *data);
+ LHASH *lh_<type>_new();
+ void lh_<type>_free(LHASH_OF(<type> *table);
 
- void lh_doall(LHASH *table, LHASH_DOALL_FN_TYPE func);
- void lh_doall_arg(LHASH *table, LHASH_DOALL_ARG_FN_TYPE func,
-          void *arg);
+ <type> *lh_<type>_insert(LHASH_OF(<type> *table, <type> *data);
+ <type> *lh_<type>_delete(LHASH_OF(<type> *table, <type> *data);
+ <type> *lh_retrieve(LHASH_OF<type> *table, <type> *data);
 
- int lh_error(LHASH *table);
+ void lh_<type>_doall(LHASH_OF(<type> *table, LHASH_DOALL_FN_TYPE func);
+ void lh_<type>_doall_arg(LHASH_OF(<type> *table, LHASH_DOALL_ARG_FN_TYPE func,
+          <type2>, <type2> *arg);
+
+ int lh_<type>_error(LHASH_OF(<type> *table);
 
  typedef int (*LHASH_COMP_FN_TYPE)(const void *, const void *);
  typedef unsigned long (*LHASH_HASH_FN_TYPE)(const void *);
  typedef void (*LHASH_DOALL_FN_TYPE)(const void *);
  typedef void (*LHASH_DOALL_ARG_FN_TYPE)(const void *, const void *);
 
 =head1 DESCRIPTION
 
-This library implements dynamic hash tables. The hash table entries
-can be arbitrary structures. Usually they consist of key and value
-fields.
+This library implements type-checked dynamic hash tables. The hash
+table entries can be arbitrary structures. Usually they consist of key
+and value fields.
 
-lh_new() creates a new B<LHASH> structure to store arbitrary data
-entries, and provides the 'hash' and 'compare' callbacks to be used in
-organising the table's entries.  The B<hash> callback takes a pointer
-to a table entry as its argument and returns an unsigned long hash
-value for its key field.  The hash value is normally truncated to a
-power of 2, so make sure that your hash function returns well mixed
-low order bits.  The B<compare> callback takes two arguments (pointers
-to two hash table entries), and returns 0 if their keys are equal,
-non-zero otherwise.  If your hash table will contain items of some
-particular type and the B<hash> and B<compare> callbacks hash/compare
-these types, then the B<DECLARE_LHASH_HASH_FN> and
-B<IMPLEMENT_LHASH_COMP_FN> macros can be used to create callback
-wrappers of the prototypes required by lh_new().  These provide
-per-variable casts before calling the type-specific callbacks written
-by the application author.  These macros, as well as those used for
-the "doall" callbacks, are defined as;
+lh_<type>_new() creates a new B<LHASH_OF(<type>> structure to store
+arbitrary data entries, and provides the 'hash' and 'compare'
+callbacks to be used in organising the table's entries.  The B<hash>
+callback takes a pointer to a table entry as its argument and returns
+an unsigned long hash value for its key field.  The hash value is
+normally truncated to a power of 2, so make sure that your hash
+function returns well mixed low order bits.  The B<compare> callback
+takes two arguments (pointers to two hash table entries), and returns
+0 if their keys are equal, non-zero otherwise.  If your hash table
+will contain items of some particular type and the B<hash> and
+B<compare> callbacks hash/compare these types, then the
+B<DECLARE_LHASH_HASH_FN> and B<IMPLEMENT_LHASH_COMP_FN> macros can be
+used to create callback wrappers of the prototypes required by
+lh_<type>_new().  These provide per-variable casts before calling the
+type-specific callbacks written by the application author.  These
+macros, as well as those used for the "doall" callbacks, are defined
+as;
 
- #define DECLARE_LHASH_HASH_FN(f_name,o_type) \
-         unsigned long f_name##_LHASH_HASH(const void *);
- #define IMPLEMENT_LHASH_HASH_FN(f_name,o_type) \
-         unsigned long f_name##_LHASH_HASH(const void *arg) { \
-                 o_type a = (o_type)arg; \
-                 return f_name(a); }
- #define LHASH_HASH_FN(f_name) f_name##_LHASH_HASH
+ #define DECLARE_LHASH_HASH_FN(name, o_type) \
+         unsigned long name##_LHASH_HASH(const void *);
+ #define IMPLEMENT_LHASH_HASH_FN(name, o_type) \
+         unsigned long name##_LHASH_HASH(const void *arg) { \
+                 const o_type *a = arg; \
+                 return name##_hash(a); }
+ #define LHASH_HASH_FN(name) name##_LHASH_HASH
 
- #define DECLARE_LHASH_COMP_FN(f_name,o_type) \
-         int f_name##_LHASH_COMP(const void *, const void *);
- #define IMPLEMENT_LHASH_COMP_FN(f_name,o_type) \
-         int f_name##_LHASH_COMP(const void *arg1, const void *arg2) { \
-                 o_type a = (o_type)arg1; \
-                 o_type b = (o_type)arg2; \
-                 return f_name(a,b); }
- #define LHASH_COMP_FN(f_name) f_name##_LHASH_COMP
+ #define DECLARE_LHASH_COMP_FN(name, o_type) \
+         int name##_LHASH_COMP(const void *, const void *);
+ #define IMPLEMENT_LHASH_COMP_FN(name, o_type) \
+         int name##_LHASH_COMP(const void *arg1, const void *arg2) { \
+                 const o_type *a = arg1;                    \
+                 const o_type *b = arg2; \
+                 return name##_cmp(a,b); }
+ #define LHASH_COMP_FN(name) name##_LHASH_COMP
 
- #define DECLARE_LHASH_DOALL_FN(f_name,o_type) \
-         void f_name##_LHASH_DOALL(const void *);
- #define IMPLEMENT_LHASH_DOALL_FN(f_name,o_type) \
-         void f_name##_LHASH_DOALL(const void *arg) { \
-                 o_type a = (o_type)arg; \
-                 f_name(a); }
- #define LHASH_DOALL_FN(f_name) f_name##_LHASH_DOALL
+ #define DECLARE_LHASH_DOALL_FN(name, o_type) \
+         void name##_LHASH_DOALL(void *);
+ #define IMPLEMENT_LHASH_DOALL_FN(name, o_type) \
+         void name##_LHASH_DOALL(void *arg) { \
+                 o_type *a = arg; \
+                 name##_doall(a); }
+ #define LHASH_DOALL_FN(name) name##_LHASH_DOALL
 
- #define DECLARE_LHASH_DOALL_ARG_FN(f_name,o_type,a_type) \
-         void f_name##_LHASH_DOALL_ARG(const void *, const void *);
- #define IMPLEMENT_LHASH_DOALL_ARG_FN(f_name,o_type,a_type) \
-         void f_name##_LHASH_DOALL_ARG(const void *arg1, const void *arg2) { \
-                 o_type a = (o_type)arg1; \
-                 a_type b = (a_type)arg2; \
-                 f_name(a,b); }
- #define LHASH_DOALL_ARG_FN(f_name) f_name##_LHASH_DOALL_ARG
+ #define DECLARE_LHASH_DOALL_ARG_FN(name, o_type, a_type) \
+         void name##_LHASH_DOALL_ARG(void *, void *);
+ #define IMPLEMENT_LHASH_DOALL_ARG_FN(name, o_type, a_type) \
+         void name##_LHASH_DOALL_ARG(void *arg1, void *arg2) { \
+                 o_type *a = arg1; \
+                 a_type *b = arg2; \
+                 name##_doall_arg(a, b); }
+ #define LHASH_DOALL_ARG_FN(name) name##_LHASH_DOALL_ARG
 
-An example of a hash table storing (pointers to) structures of type 'STUFF'
-could be defined as follows;
+ An example of a hash table storing (pointers to) structures of type 'STUFF'
+ could be defined as follows;
 
  /* Calculates the hash value of 'tohash' (implemented elsewhere) */
  unsigned long STUFF_hash(const STUFF *tohash);
  /* Orders 'arg1' and 'arg2' (implemented elsewhere) */
- int STUFF_cmp(const STUFF *arg1, const STUFF *arg2);
+ int stuff_cmp(const STUFF *arg1, const STUFF *arg2);
  /* Create the type-safe wrapper functions for use in the LHASH internals */
- static IMPLEMENT_LHASH_HASH_FN(STUFF_hash, const STUFF *)
- static IMPLEMENT_LHASH_COMP_FN(STUFF_cmp, const STUFF *);
+ static IMPLEMENT_LHASH_HASH_FN(stuff, STUFF);
+ static IMPLEMENT_LHASH_COMP_FN(stuff, STUFF);
  /* ... */
  int main(int argc, char *argv[]) {
          /* Create the new hash table using the hash/compare wrappers */
-         LHASH *hashtable = lh_new(LHASH_HASH_FN(STUFF_hash),
+         LHASH_OF(STUFF) *hashtable = lh_STUFF_new(LHASH_HASH_FN(STUFF_hash),
                                    LHASH_COMP_FN(STUFF_cmp));
          /* ... */
  }
 
-lh_free() frees the B<LHASH> structure B<table>. Allocated hash table
-entries will not be freed; consider using lh_doall() to deallocate any
-remaining entries in the hash table (see below).
+lh_<type>_free() frees the B<LHASH_OF(<type>> structure
+B<table>. Allocated hash table entries will not be freed; consider
+using lh_<type>_doall() to deallocate any remaining entries in the
+hash table (see below).
 
-lh_insert() inserts the structure pointed to by B<data> into B<table>.
-If there already is an entry with the same key, the old value is
-replaced. Note that lh_insert() stores pointers, the data are not
-copied.
+lh_<type>_insert() inserts the structure pointed to by B<data> into
+B<table>.  If there already is an entry with the same key, the old
+value is replaced. Note that lh_<type>_insert() stores pointers, the
+data are not copied.
 
-lh_delete() deletes an entry from B<table>.
+lh_<type>_delete() deletes an entry from B<table>.
 
-lh_retrieve() looks up an entry in B<table>. Normally, B<data> is
-a structure with the key field(s) set; the function will return a
+lh_<type>_retrieve() looks up an entry in B<table>. Normally, B<data>
+is a structure with the key field(s) set; the function will return a
 pointer to a fully populated structure.
 
-lh_doall() will, for every entry in the hash table, call B<func> with
-the data item as its parameter.  For lh_doall() and lh_doall_arg(),
-function pointer casting should be avoided in the callbacks (see
-B<NOTE>) - instead, either declare the callbacks to match the
-prototype required in lh_new() or use the declare/implement macros to
-create type-safe wrappers that cast variables prior to calling your
-type-specific callbacks.  An example of this is illustrated here where
-the callback is used to cleanup resources for items in the hash table
-prior to the hashtable itself being deallocated:
+lh_<type>_doall() will, for every entry in the hash table, call
+B<func> with the data item as its parameter.  For lh_<type>_doall()
+and lh_<type>_doall_arg(), function pointer casting should be avoided
+in the callbacks (see B<NOTE>) - instead use the declare/implement
+macros to create type-checked wrappers that cast variables prior to
+calling your type-specific callbacks.  An example of this is
+illustrated here where the callback is used to cleanup resources for
+items in the hash table prior to the hashtable itself being
+deallocated:
 
  /* Cleans up resources belonging to 'a' (this is implemented elsewhere) */
- void STUFF_cleanup(STUFF *a);
+ void STUFF_cleanup_doall(STUFF *a);
  /* Implement a prototype-compatible wrapper for "STUFF_cleanup" */
- IMPLEMENT_LHASH_DOALL_FN(STUFF_cleanup, STUFF *)
+ IMPLEMENT_LHASH_DOALL_FN(STUFF_cleanup, STUFF)
          /* ... then later in the code ... */
  /* So to run "STUFF_cleanup" against all items in a hash table ... */
- lh_doall(hashtable, LHASH_DOALL_FN(STUFF_cleanup));
+ lh_STUFF_doall(hashtable, LHASH_DOALL_FN(STUFF_cleanup));
  /* Then the hash table itself can be deallocated */
- lh_free(hashtable);
+ lh_STUFF_free(hashtable);
 
 When doing this, be careful if you delete entries from the hash table
 in your callbacks: the table may decrease in size, moving the item
 that you are currently on down lower in the hash table - this could
 cause some entries to be skipped during the iteration.  The second
 best solution to this problem is to set hash-E<gt>down_load=0 before
 you start (which will stop the hash table ever decreasing in size).
 The best solution is probably to avoid deleting items from the hash
 table inside a "doall" callback!
 
-lh_doall_arg() is the same as lh_doall() except that B<func> will be
-called with B<arg> as the second argument and B<func> should be of
-type B<LHASH_DOALL_ARG_FN_TYPE> (a callback prototype that is passed
-both the table entry and an extra argument).  As with lh_doall(), you
-can instead choose to declare your callback with a prototype matching
-the types you are dealing with and use the declare/implement macros to
-create compatible wrappers that cast variables before calling your
-type-specific callbacks.  An example of this is demonstrated here
-(printing all hash table entries to a BIO that is provided by the
-caller):
+lh_<type>_doall_arg() is the same as lh_<type>_doall() except that
+B<func> will be called with B<arg> as the second argument and B<func>
+should be of type B<LHASH_DOALL_ARG_FN_TYPE> (a callback prototype
+that is passed both the table entry and an extra argument).  As with
+lh_doall(), you can instead choose to declare your callback with a
+prototype matching the types you are dealing with and use the
+declare/implement macros to create compatible wrappers that cast
+variables before calling your type-specific callbacks.  An example of
+this is demonstrated here (printing all hash table entries to a BIO
+that is provided by the caller):
 
  /* Prints item 'a' to 'output_bio' (this is implemented elsewhere) */
- void STUFF_print(const STUFF *a, BIO *output_bio);
+ void STUFF_print_doall_arg(const STUFF *a, BIO *output_bio);
  /* Implement a prototype-compatible wrapper for "STUFF_print" */
- static IMPLEMENT_LHASH_DOALL_ARG_FN(STUFF_print, const STUFF *, BIO *)
+ static IMPLEMENT_LHASH_DOALL_ARG_FN(STUFF, const STUFF, BIO)
          /* ... then later in the code ... */
  /* Print out the entire hashtable to a particular BIO */
- lh_doall_arg(hashtable, LHASH_DOALL_ARG_FN(STUFF_print), logging_bio);
+ lh_STUFF_doall_arg(hashtable, LHASH_DOALL_ARG_FN(STUFF_print), BIO,
+                    logging_bio);
  
-lh_error() can be used to determine if an error occurred in the last
-operation. lh_error() is a macro.
+lh_<type>_error() can be used to determine if an error occurred in the last
+operation. lh_<type>_error() is a macro.
 
 =head1 RETURN VALUES
 
-lh_new() returns B<NULL> on error, otherwise a pointer to the new
+lh_<type>_new() returns B<NULL> on error, otherwise a pointer to the new
 B<LHASH> structure.
 
-When a hash table entry is replaced, lh_insert() returns the value
+When a hash table entry is replaced, lh_<type>_insert() returns the value
 being replaced. B<NULL> is returned on normal operation and on error.
 
-lh_delete() returns the entry being deleted.  B<NULL> is returned if
+lh_<type>_delete() returns the entry being deleted.  B<NULL> is returned if
 there is no such value in the hash table.
 
-lh_retrieve() returns the hash table entry if it has been found,
+lh_<type>_retrieve() returns the hash table entry if it has been found,
 B<NULL> otherwise.
 
-lh_error() returns 1 if an error occurred in the last operation, 0
+lh_<type>_error() returns 1 if an error occurred in the last operation, 0
 otherwise.
 
-lh_free(), lh_doall() and lh_doall_arg() return no values.
+lh_<type>_free(), lh_<type>_doall() and lh_<type>_doall_arg() return no values.
 
 =head1 NOTE
 
 The various LHASH macros and callback types exist to make it possible
-to write type-safe code without resorting to function-prototype
+to write type-checked code without resorting to function-prototype
 casting - an evil that makes application code much harder to
 audit/verify and also opens the window of opportunity for stack
 corruption and other hard-to-find bugs.  It also, apparently, violates
 ANSI-C.
 
 The LHASH code regards table entries as constant data.  As such, it
 internally represents lh_insert()'d items with a "const void *"
 pointer type.  This is why callbacks such as those used by lh_doall()
 and lh_doall_arg() declare their prototypes with "const", even for the
 parameters that pass back the table items' data pointers - for
@@ skipping 17 matching lines @@
 Callers that only have "const" access to data they're indexing in a
 table, yet declare callbacks without constant types (or cast the
 "const" away themselves), are therefore creating their own risks/bugs
 without being encouraged to do so by the API.  On a related note,
 those auditing code should pay special attention to any instances of
 DECLARE/IMPLEMENT_LHASH_DOALL_[ARG_]_FN macros that provide types
 without any "const" qualifiers.
 
 =head1 BUGS
 
-lh_insert() returns B<NULL> both for success and error.
+lh_<type>_insert() returns B<NULL> both for success and error.
 
 =head1 INTERNALS
 
 The following description is based on the SSLeay documentation:
 
 The B<lhash> library implements a hash table described in the
 I<Communications of the ACM> in 1991.  What makes this hash table
 different is that as the table fills, the hash table is increased (or
 decreased) in size via OPENSSL_realloc().  When a 'resize' is done, instead of
 all hashes being redistributed over twice as many 'buckets', one
@@ skipping 24 matching lines @@
 probably worth changing your hash function if this is the case because
 even if your hash table has 10 items in a 'bucket', it can be searched
 with 10 B<unsigned long> compares and 10 linked list traverses.  This
 will be much less expensive that 10 calls to your compare function.
 
 lh_strhash() is a demo string hashing function:
 
  unsigned long lh_strhash(const char *c);
 
 Since the B<LHASH> routines would normally be passed structures, this
-routine would not normally be passed to lh_new(), rather it would be
-used in the function passed to lh_new().
+routine would not normally be passed to lh_<type>_new(), rather it would be
+used in the function passed to lh_<type>_new().
 
 =head1 SEE ALSO
 
 L<lh_stats(3)|lh_stats(3)>
 
 =head1 HISTORY
 
 The B<lhash> library is available in all versions of SSLeay and OpenSSL.
 lh_error() was added in SSLeay 0.9.1b.
 
 This manpage is derived from the SSLeay documentation.
 
 In OpenSSL 0.9.7, all lhash functions that were passed function pointers
 were changed for better type safety, and the function types LHASH_COMP_FN_TYPE,
 LHASH_HASH_FN_TYPE, LHASH_DOALL_FN_TYPE and LHASH_DOALL_ARG_FN_TYPE 
 became available.
 
+In OpenSSL 1.0.0, the lhash interface was revamped for even better
+type checking.
+
 =cut