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Allow non-power-of-2 signature cache sizes

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This commit is contained in:
Pieter Wuille 2017-01-12 10:16:31 -08:00
parent 02e5308c1b
commit 7482781347
1 changed files with 11 additions and 18 deletions
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29
src/cuckoocache.h
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@ -154,7 +154,7 @@ public:
* @tparam Element should be a movable and copyable type * @tparam Element should be a movable and copyable type
* @tparam Hash should be a function/callable which takes a template parameter * @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 * 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> template <typename Element, typename Hash>
class cache class cache
@ -193,12 +193,6 @@ private:
*/ */
uint32_t epoch_size; 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. /** depth_limit determines how many elements insert should try to replace.
* Should be set to log2(n)*/ * Should be set to log2(n)*/
uint8_t depth_limit; uint8_t depth_limit;
@ -217,14 +211,14 @@ private:
*/ */
inline std::array<uint32_t, 8> compute_hashes(const Element& e) const inline std::array<uint32_t, 8> compute_hashes(const Element& e) const
{ {
return {{hash_function.template operator()<0>(e) & hash_mask, return {{(uint32_t)((hash_function.template operator()<0>(e) * (uint64_t)size) >> 32),
hash_function.template operator()<1>(e) & hash_mask, (uint32_t)((hash_function.template operator()<1>(e) * (uint64_t)size) >> 32),
hash_function.template operator()<2>(e) & hash_mask, (uint32_t)((hash_function.template operator()<2>(e) * (uint64_t)size) >> 32),
hash_function.template operator()<3>(e) & hash_mask, (uint32_t)((hash_function.template operator()<3>(e) * (uint64_t)size) >> 32),
hash_function.template operator()<4>(e) & hash_mask, (uint32_t)((hash_function.template operator()<4>(e) * (uint64_t)size) >> 32),
hash_function.template operator()<5>(e) & hash_mask, (uint32_t)((hash_function.template operator()<5>(e) * (uint64_t)size) >> 32),
hash_function.template operator()<6>(e) & hash_mask, (uint32_t)((hash_function.template operator()<6>(e) * (uint64_t)size) >> 32),
hash_function.template operator()<7>(e) & hash_mask}}; (uint32_t)((hash_function.template operator()<7>(e) * (uint64_t)size) >> 32)}};
} }
/* end /* end
@ -305,7 +299,7 @@ public:
} }
/** setup initializes the container to store no more than new_size /** 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. * setup should only be called once.
* *
@ -316,8 +310,7 @@ public:
{ {
// depth_limit must be at least one otherwise errors can occur. // 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)))); depth_limit = static_cast<uint8_t>(std::log2(static_cast<float>(std::max((uint32_t)2, new_size))));
size = 1 << depth_limit; size = std::max<uint32_t>(2, new_size);
hash_mask = size-1;
table.resize(size); table.resize(size);
collection_flags.setup(size); collection_flags.setup(size);
epoch_flags.resize(size); epoch_flags.resize(size);