Replace hash_gid with FNV-1a
#422
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We seem to have many uses of |
clalancette
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Jan 23, 2025
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| // This function implemented FNV-1a 64-bit as the GID is small enough | ||
| // (e.g. as of commit db4d05e of ros2/rmw RMW_GID_STORAGE_SIZE is set to 16) | ||
| // and FNV is known to be efficient in such cases. | ||
| // | ||
| // See https://github.com/ros2/rmw/blob/db4d05e/rmw/include/rmw/types.h#L44 | ||
| // and https://datatracker.ietf.org/doc/html/draft-eastlake-fnv-17.html | ||
| static constexpr uint64_t FNV_OFFSET_BASIS_64 = 0x00000100000001b3; | ||
| static constexpr uint64_t FNV_PRIME_64 = 0xcbf29ce484222325; |
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So we are already using xxhash3 in liveliness_utils to take a string and hash it into a 128-bit quantity. Do we need to hash again? In other words, could we just use the 128-bit GID directly and use that as the key?
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hash_gidis called on Zenoh subscriber callbacks and shows up when profiling as a hot function. The use ofstd::stringstreamseems to be relatively inefficient. A significant portion ofhash_gid's running time is spend allocating & deallocating thestd::stringstream.