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76 lines
2.2 KiB
76 lines
2.2 KiB
sha1-array API |
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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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Data Structures |
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--------------- |
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`struct sha1_array`:: |
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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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Functions |
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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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`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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`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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`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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Examples |
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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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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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/* 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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/* 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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* 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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-----------------------------------------
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