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use memset for group array initialization only when permissible

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This commit is contained in:
joaquintides
2023-03-31 19:36:31 +02:00
parent b86dee9a18
commit d22787c218
1 changed files with 26 additions and 9 deletions
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35
include/boost/unordered/detail/foa/core.hpp
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@ -163,11 +163,12 @@ static constexpr std::size_t default_bucket_count=0;
* "logical" 128-bit word, and so forth. With this layout, match can be
* implemented with 4 ANDs, 3 shifts, 2 XORs, 1 OR and 1 NOT.
*
* TODO: Explain IntegralWrapper.
*
* group15 has no user-defined ctor so that it's a trivial type and can be
* initialized via memset etc. Where needed, group15::initialize sets the
* metadata to all zeros.
* IntegralWrapper<Integral> is used to implement group15's underlying
* metadata: it behaves as a plain integral for foa::table or introduces
* atomic ops for foa::concurrent_table. If IntegralWrapper<...> is trivially
* constructible, so is group15, in which case it can be initialized via memset
* etc. Where needed, group15::initialize resets the metadata to the all
* zeros (default state).
*/
#if defined(BOOST_UNORDERED_SSE2)
@ -937,10 +938,10 @@ struct table_arrays
reinterpret_cast<uintptr_t>(p))%sizeof(group_type);
arrays.groups=reinterpret_cast<group_type*>(p);
/* memset is faster/not slower than initializing groups individually.
* This assumes all zeros is group_type's default layout.
*/
std::memset(arrays.groups,0,sizeof(group_type)*groups_size);
initialize_groups(
arrays.groups,groups_size,
std::integral_constant<
bool,std::is_trivially_constructible<group_type>::value>{});
arrays.groups[groups_size-1].set_sentinel();
}
return arrays;
@ -976,6 +977,22 @@ struct table_arrays
return (buffer_bytes+sizeof(value_type)-1)/sizeof(value_type);
}
static void initialize_groups(
group_type* groups_,std::size_t size,std::true_type /* memset */)
{
/* Faster/not slower than manual, assumes all zeros is group_type's
* default layout.
*/
std::memset(groups_,0,sizeof(group_type)*size);
}
static void initialize_groups(
group_type* groups_,std::size_t size,std::false_type /* manual */)
{
while(size--!=0)::new (groups_++) group_type();
}
std::size_t groups_size_index;
std::size_t groups_size_mask;
group_type *groups;