This API was introduced in 902bb36, but never documented.
Let's be nice to future users of the code.
Signed-off-by: Jeff King <peff@xxxxxxxx>
---
Documentation/technical/api-sha1-array.txt | 79 ++++++++++++++++++++++++++++
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+sha1-array API
+==============
+
+The sha1-array API provides storage and manipulation of sets of SHA1
+identifiers. The emphasis is on storage and processing efficiency,
+making them suitable for large lists. Note that the ordering of items is
+not preserved over some operations.
+
+Data Structures
+---------------
+
+`struct sha1_array`::
+
+ A single array of SHA1 hashes. This should be initialized by
+ assignment from `SHA1_ARRAY_INIT`. The `sha1` member contains
+ the actual data. The `nr` member contains the number of items in
+ the set. The `alloc` and `sorted` members are used internally,
+ and should not be needed by API callers.
+
+Functions
+---------
+
+`sha1_array_append`::
+ Add an item to the set. The sha1 will be placed at the end of
+ the array (but note that some operations below may lose this
+ ordering).
+
+`sha1_array_sort`::
+ Sort the elements in the array.
+
+`sha1_array_lookup`::
+ Perform a binary search of the array for a specific sha1.
+ If found, returns the offset (in number of elements) of the
+ sha1. If not found, returns a negative integer. If the array is
+ not sorted, this function has the side effect of sorting it.
+
+`sha1_array_clear`::
+ Free all memory associated with the array and return it to the
+ initial, empty state.
+
+`sha1_array_for_each_unique`::
+ Efficiently iterate over each unique element of the list,
+ executing the callback function for each one. If the array is
+ not sorted, this function has the side effect of sorting it.
+
+Examples
+--------
+
+-----------------------------------------
+void print_callback(const unsigned char sha1[20],
+ void *data)
+{
+ printf("%s\n", sha1_to_hex(sha1));
+}
+
+void some_func(void)
+{
+ struct sha1_array hashes = SHA1_ARRAY_INIT;
+ unsigned char sha1[20];
+
+ /* Read objects into our set */
+ while (read_object_from_stdin(sha1))
+ sha1_array_append(&hashes, sha1);
+
+ /* Check if some objects are in our set */
+ while (read_object_from_stdin(sha1)) {
+ if (sha1_array_lookup(&hashes, sha1) >= 0)
+ printf("it's in there!\n");
+
+ /*
+ * Print the unique set of objects. We could also have
+ * avoided adding duplicate objects in the first place,
+ * but we would end up re-sorting the array repeatedly.
+ * Instead, this will sort once and then skip duplicates
+ * in linear time.
+ */
+ sha1_array_for_each_unique(&hashes, print_callback, NULL);
+}
+-----------------------------------------
--
1.7.7.rc1.2.gb2409
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