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perf: optimize GenerateRandomString() (#66)

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The previous implementation used an std::stringstream to concatenate
the generated random string.

The new one uses a simple preallocated std::string, as the size of the
output is already known - it is the length parameter.

It also uses std::generate_n() instead of an explicit loop, making the
code more concise and potentially faster, as no calls to
std::string::operator+= are needed.

Calling GenerateRandomString(1'000'000) with the std::stringstream-based
implementation allocated 16 times, for a total of 3'173'516 bytes.
The new one cuts this down to 4 allocs, for a total of 1'076'864 bytes.
This commit is contained in:
Andrea Pappacoda 2022-08-26 12:53:42 +02:00 committed by GitHub
parent 723fd8cbef
commit 19a0a3a359
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1 changed files with 10 additions and 8 deletions
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18
src/util/helpers/helpers.cpp
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@ -419,18 +419,20 @@ std::string GenerateRandomString(size_t length)
return GenerateRandomString(length, kCharacters);
}
std::string GenerateRandomString(size_t length, std::string_view characters)
std::string GenerateRandomString(const size_t length, const std::string_view characters)
{
assert(!characters.empty());
std::stringstream result;
std::string result;
result.resize(length);
std::random_device rd;
std::mt19937 gen(rd());
std::uniform_int_distribution<decltype(characters.size())> index_dist(0, characters.size() - 1);
for (uint32_t i = 0; i < length; ++i)
{
result << characters[index_dist(gen)];
}
std::generate_n(
result.begin(),
length,
[&] { return characters[index_dist(gen)]; }
);
return result.str();
}
return result;
}