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libstdc++: Optimize std::seed_seq construction

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When std::seed_seq is constructed from random access iterators we can
detect the internal vector size in O(1). Reserving memory for elements
in such cases may avoid multiple memory allocations.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/random.tcc (seed_seq::seed_seq): Reserve capacity
	if distance is O(1).
	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error
	line number.

Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
This commit is contained in:
Antony Polukhin 2021-08-17 13:50:53 +01:00 committed by Jonathan Wakely
parent 897a15f355
commit 174f9257a7
2 changed files with 5 additions and 1 deletions
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4
libstdc++-v3/include/bits/random.tcc
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@ -3240,6 +3240,7 @@ namespace __detail
template<typename _IntType, typename>
seed_seq::seed_seq(std::initializer_list<_IntType> __il)
{
_M_v.reserve(__il.size());
for (auto __iter = __il.begin(); __iter != __il.end(); ++__iter)
_M_v.push_back(__detail::__mod<result_type,
__detail::_Shift<result_type, 32>::__value>(*__iter));
@ -3248,6 +3249,9 @@ namespace __detail
template<typename _InputIterator>
seed_seq::seed_seq(_InputIterator __begin, _InputIterator __end)
{
if _GLIBCXX17_CONSTEXPR (__is_random_access_iter<_InputIterator>::value)
_M_v.reserve(std::distance(__begin, __end));
for (_InputIterator __iter = __begin; __iter != __end; ++__iter)
_M_v.push_back(__detail::__mod<result_type,
__detail::_Shift<result_type, 32>::__value>(*__iter));

2
libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc
View File

@ -12,4 +12,4 @@ auto x = std::generate_canonical<std::size_t,
// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 169 }
// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 3352 }
// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 3356 }