add sha1_array API docs
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@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Jeff King committed
Sep 13, 2011 at 17:57 UTC
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Documentation/technical/api-sha1-array.txt
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+sha1-array API
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+==============
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+
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+The sha1-array API provides storage and manipulation of sets of SHA1
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+identifiers. The emphasis is on storage and processing efficiency,
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+making them suitable for large lists. Note that the ordering of items is
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+not preserved over some operations.
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+
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+Data Structures
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+---------------
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+
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+`struct sha1_array`::
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+
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+ A single array of SHA1 hashes. This should be initialized by
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+ assignment from `SHA1_ARRAY_INIT`. The `sha1` member contains
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+ the actual data. The `nr` member contains the number of items in
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+ the set. The `alloc` and `sorted` members are used internally,
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+ and should not be needed by API callers.
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+
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+Functions
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+---------
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+
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+`sha1_array_append`::
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+ Add an item to the set. The sha1 will be placed at the end of
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+ the array (but note that some operations below may lose this
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+ ordering).
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+
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+`sha1_array_sort`::
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+ Sort the elements in the array.
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+
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+`sha1_array_lookup`::
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+ Perform a binary search of the array for a specific sha1.
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+ If found, returns the offset (in number of elements) of the
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+ sha1. If not found, returns a negative integer. If the array is
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+ not sorted, this function has the side effect of sorting it.
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+
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+`sha1_array_clear`::
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+ Free all memory associated with the array and return it to the
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+ initial, empty state.
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+
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+`sha1_array_for_each_unique`::
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+ Efficiently iterate over each unique element of the list,
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+ executing the callback function for each one. If the array is
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+ not sorted, this function has the side effect of sorting it.
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+
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+Examples
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+--------
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+
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+-----------------------------------------
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+void print_callback(const unsigned char sha1[20],
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+ void *data)
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+{
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+ printf("%s\n", sha1_to_hex(sha1));
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+}
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+
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+void some_func(void)
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+{
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+ struct sha1_array hashes = SHA1_ARRAY_INIT;
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+ unsigned char sha1[20];
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+
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+ /* Read objects into our set */
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+ while (read_object_from_stdin(sha1))
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+ sha1_array_append(&hashes, sha1);
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+
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+ /* Check if some objects are in our set */
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+ while (read_object_from_stdin(sha1)) {
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+ if (sha1_array_lookup(&hashes, sha1) >= 0)
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+ printf("it's in there!\n");
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+
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+ /*
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+ * Print the unique set of objects. We could also have
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+ * avoided adding duplicate objects in the first place,
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+ * but we would end up re-sorting the array repeatedly.
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+ * Instead, this will sort once and then skip duplicates
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+ * in linear time.
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+ */
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+ sha1_array_for_each_unique(&hashes, print_callback, NULL);
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+}
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+-----------------------------------------