thin-provisioning-tools/base/sequence_generator.cc

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#include "base/run_set.h"
#include "base/sequence_generator.h"
#include <chrono>
#include <random>
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#include <stdexcept>
//----------------------------------------------------------------
namespace {
// - The maximum generated value is not greater than (begin+size)
// - The generated values are not aligned to the step, if the begin
// value is not aligned.
class forward_sequence_generator: public base::sequence_generator {
public:
forward_sequence_generator(uint64_t begin,
uint64_t size,
uint64_t step)
: begin_(begin),
step_(step),
current_(begin),
rounds_(0)
{
verify_parameters(size, step);
end_ = begin + (size / step) * step;
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}
forward_sequence_generator()
: begin_(0), end_(1), step_(1),
current_(0), rounds_(0) {
}
uint64_t next() {
uint64_t r = current_;
current_ += step_;
if (current_ >= end_) {
current_ = begin_;
++rounds_;
}
return r;
}
void reset(uint64_t begin, uint64_t size, uint64_t step = 1) {
verify_parameters(size, step);
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begin_ = begin;
end_ = begin + (size / step) * step;
step_ = step;
current_ = begin;
rounds_ = 0;
}
static void verify_parameters(uint64_t size, uint64_t step) {
if (!size || !step)
throw std::runtime_error("size or step must be non-zero");
if (size < step)
throw std::runtime_error("size must be greater than the step");
}
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uint64_t get_rounds() {
return rounds_;
}
private:
uint64_t begin_;
uint64_t end_;
uint64_t step_;
uint64_t current_;
uint64_t rounds_;
};
// - The maximum generated value is not greater than (begin+size)
// - The generated values are not aligned to the step, if the begin
// value is not aligned.
class random_sequence_generator: public base::sequence_generator {
public:
// TODO: load random seeds
random_sequence_generator(uint64_t begin,
uint64_t size,
uint64_t step,
unsigned seq_nr = 1)
: begin_(begin),
step_(step),
max_forward_steps_(seq_nr),
rand_seed_(std::chrono::high_resolution_clock::now().time_since_epoch().count()),
results_engine_(rand_seed_),
steps_engine_(rand_seed_),
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nr_generated_(0)
{
if (!size || !step || !seq_nr)
throw std::runtime_error("size, step, or forward steps must be non-zero");
if (size < step)
throw std::runtime_error("size must be greater than the step");
nr_steps_ = size / step;
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if (!max_forward_steps_ || max_forward_steps_ > nr_steps_)
throw std::runtime_error("invalid number of forward steps");
results_distr_ = std::uniform_int_distribution<uint64_t>(0,
nr_steps_ - 1);
if (max_forward_steps_ > 1) {
steps_distr_ = std::uniform_int_distribution<uint64_t>(1,
max_forward_steps_);
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reset_forward_generator();
}
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}
uint64_t next() {
// FIXME: eliminate if-else
uint64_t step_idx = (max_forward_steps_ > 1) ?
next_forward_step() : next_random_step();
return begin_ + step_idx * step_;
}
private:
void reset_forward_generator() {
uint64_t begin = peek_random_step();
unsigned seq_nr = steps_distr_(steps_engine_);
base::run_set<uint64_t>::const_iterator it = rand_map_.upper_bound(begin);
if (it != rand_map_.end())
seq_nr = std::min<uint64_t>(seq_nr, *it->begin_ - begin);
else
seq_nr = std::min<uint64_t>(seq_nr, nr_steps_ - begin);
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forward_gen_.reset(begin, seq_nr);
}
uint64_t next_forward_step() {
uint64_t step_idx = forward_gen_.next();
consume_random_map(step_idx);
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if (forward_gen_.get_rounds())
reset_forward_generator();
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return step_idx;
}
uint64_t next_random_step() {
uint64_t step_idx = peek_random_step();
consume_random_map(step_idx);
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return step_idx;
}
void consume_random_map(uint64_t step_idx) {
rand_map_.add(step_idx);
++nr_generated_;
// wrap-around
if (nr_generated_ == nr_steps_) {
rand_map_.clear();
nr_generated_ = 0;
}
}
// TODO: improve the complexity of generating unique sequence
uint64_t peek_random_step() {
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uint64_t step_idx;
bool found = true;
while (found) {
step_idx = results_distr_(results_engine_);
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found = rand_map_.member(step_idx);
}
return step_idx;
}
uint64_t begin_;
uint64_t nr_steps_;
uint64_t step_;
unsigned max_forward_steps_;
uint64_t rand_seed_;
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std::mt19937_64 results_engine_;
std::mt19937_64 steps_engine_;
std::uniform_int_distribution<uint64_t> results_distr_;
std::uniform_int_distribution<uint64_t> steps_distr_;
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base::run_set<uint64_t> rand_map_;
uint64_t nr_generated_;
forward_sequence_generator forward_gen_;
};
}
//----------------------------------------------------------------
base::sequence_generator::ptr
base::create_forward_sequence_generator(uint64_t begin,
uint64_t size,
uint64_t step)
{
return sequence_generator::ptr(
new forward_sequence_generator(begin, size, step));
}
base::sequence_generator::ptr
base::create_random_sequence_generator(uint64_t begin,
uint64_t size,
uint64_t step,
unsigned seq_nr)
{
return sequence_generator::ptr(
new random_sequence_generator(begin, size, step, seq_nr));
}
//----------------------------------------------------------------