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Allow non-power-of-2 signature cache sizes #9533

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merged 1 commit into from Apr 3, 2017
Merged

Allow non-power-of-2 signature cache sizes #9533

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29 changes: 11 additions & 18 deletions src/cuckoocache.h
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Expand Up @@ -154,7 +154,7 @@ class bit_packed_atomic_flags
* @tparam Element should be a movable and copyable type
* @tparam Hash should be a function/callable which takes a template parameter
* hash_select and an Element and extracts a hash from it. Should return
* high-entropy hashes for `Hash h; h<0>(e) ... h<7>(e)`.
* high-entropy uint32_t hashes for `Hash h; h<0>(e) ... h<7>(e)`.
*/
template <typename Element, typename Hash>
class cache
Expand Down Expand Up @@ -193,12 +193,6 @@ class cache
*/
uint32_t epoch_size;

/** hash_mask should be set to appropriately mask out a hash such that every
* masked hash is [0,size), eg, if floor(log2(size)) == 20, then hash_mask
* should be (1<<20)-1
*/
uint32_t hash_mask;

/** depth_limit determines how many elements insert should try to replace.
* Should be set to log2(n)*/
uint8_t depth_limit;
Expand All @@ -217,14 +211,14 @@ class cache
*/
inline std::array<uint32_t, 8> compute_hashes(const Element& e) const
{
return {{hash_function.template operator()<0>(e) & hash_mask,
hash_function.template operator()<1>(e) & hash_mask,
hash_function.template operator()<2>(e) & hash_mask,
hash_function.template operator()<3>(e) & hash_mask,
hash_function.template operator()<4>(e) & hash_mask,
hash_function.template operator()<5>(e) & hash_mask,
hash_function.template operator()<6>(e) & hash_mask,
hash_function.template operator()<7>(e) & hash_mask}};
return {{(uint32_t)((hash_function.template operator()<0>(e) * (uint64_t)size) >> 32),
(uint32_t)((hash_function.template operator()<1>(e) * (uint64_t)size) >> 32),
(uint32_t)((hash_function.template operator()<2>(e) * (uint64_t)size) >> 32),
(uint32_t)((hash_function.template operator()<3>(e) * (uint64_t)size) >> 32),
(uint32_t)((hash_function.template operator()<4>(e) * (uint64_t)size) >> 32),
(uint32_t)((hash_function.template operator()<5>(e) * (uint64_t)size) >> 32),
(uint32_t)((hash_function.template operator()<6>(e) * (uint64_t)size) >> 32),
(uint32_t)((hash_function.template operator()<7>(e) * (uint64_t)size) >> 32)}};
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@dcousens dcousens Jan 13, 2017 •
edited

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maybe a small inline function/macro would be easier to read than this?

}

/* end
Expand Down Expand Up @@ -305,7 +299,7 @@ class cache
}

/** setup initializes the container to store no more than new_size
* elements. setup rounds down to a power of two size.
* elements.
*
* setup should only be called once.
*
Expand All @@ -316,8 +310,7 @@ class cache
{
// depth_limit must be at least one otherwise errors can occur.
depth_limit = static_cast<uint8_t>(std::log2(static_cast<float>(std::max((uint32_t)2, new_size))));
size = 1 << depth_limit;
hash_mask = size-1;
size = std::max<uint32_t>(2, new_size);
table.resize(size);
collection_flags.setup(size);
epoch_flags.resize(size);
Expand Down