technical-docs: document hash API
Signed-off-by: Stephen Boyd <bebarino@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/technical/api-hash.txt b/Documentation/technical/api-hash.txt
index c784d3e..e5061e0 100644
--- a/Documentation/technical/api-hash.txt
+++ b/Documentation/technical/api-hash.txt
@@ -1,6 +1,52 @@
hash API
========
-Talk about <hash.h>
+The hash API is a collection of simple hash table functions. Users are expected
+to implement their own hashing.
-(Linus)
+Data Structures
+---------------
+
+`struct hash_table`::
+
+ The hash table structure. The `array` member points to the hash table
+ entries. The `size` member counts the total number of valid and invalid
+ entries in the table. The `nr` member keeps track of the number of
+ valid entries.
+
+`struct hash_table_entry`::
+
+ An opaque structure representing an entry in the hash table. The `hash`
+ member is the entry's hash key and the `ptr` member is the entry's
+ value.
+
+Functions
+---------
+
+`init_hash`::
+
+ Initialize the hash table.
+
+`free_hash`::
+
+ Release memory associated with the hash table.
+
+`insert_hash`::
+
+ Insert a pointer into the hash table. If an entry with that hash
+ already exists, a pointer to the existing entry's value is returned.
+ Otherwise NULL is returned. This allows callers to implement
+ chaining, etc.
+
+`lookup_hash`::
+
+ Lookup an entry in the hash table. If an entry with that hash exists
+ the entry's value is returned. Otherwise NULL is returned.
+
+`for_each_hash`::
+
+ Call a function for each entry in the hash table. The function is
+ expected to take the entry's value as its only argument and return an
+ int. If the function returns a negative int the loop is aborted
+ immediately. Otherwise, the return value is accumulated and the sum
+ returned upon completion of the loop.
