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/*
* nextpnr -- Next Generation Place and Route
*
* Copyright (C) 2021 Symbiflow Authors
*
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
*/
#include "sampler.h"
#include <algorithm>
#include <cmath>
#include <stdexcept>
NEXTPNR_NAMESPACE_BEGIN
static size_t partition_x(std::vector<size_t>::iterator begin, std::vector<size_t>::iterator end,
const std::vector<std::pair<int32_t, int32_t>> &samples)
{
if (std::distance(begin, end) == 0) {
return 0;
}
// Find the median x value.
std::vector<int32_t> xs;
xs.reserve(std::distance(begin, end));
for (auto iter = begin; iter != end; ++iter) {
xs.push_back(samples[*iter].first);
}
std::sort(xs.begin(), xs.end());
xs.erase(std::unique(xs.begin(), xs.end()), xs.end());
// Partion on the median x value (e.g. 50% of samples on one side and
// 50% of samples on the other side).
int32_t x_div = xs[(xs.size() - 1) / 2];
auto split = std::partition(begin, end,
[x_div, &samples](size_t index) -> bool { return samples[index].first <= x_div; });
return std::distance(begin, split);
}
/* Don't both splitting when the partition has less than kMinSplit. */
static constexpr ptrdiff_t kMinSplit = 20;
static size_t partition_y(std::vector<size_t>::iterator begin, std::vector<size_t>::iterator end,
const std::vector<std::pair<int32_t, int32_t>> &samples)
{
if (std::distance(begin, end) == 0) {
return 0;
}
std::vector<int32_t> ys;
ys.reserve(std::distance(begin, end));
for (auto iter = begin; iter != end; ++iter) {
ys.push_back(samples[*iter].second);
}
std::sort(ys.begin(), ys.end());
ys.erase(std::unique(ys.begin(), ys.end()), ys.end());
int32_t y_div = ys[(ys.size() - 1) / 2];
auto split = std::partition(begin, end,
[y_div, &samples](size_t index) -> bool { return samples[index].second <= y_div; });
return std::distance(begin, split);
}
static void add_split(std::vector<size_t> *splits, size_t new_split)
{
if (splits->back() < new_split) {
splits->push_back(new_split);
} else if (splits->back() != new_split) {
throw std::runtime_error("Split is not consectutive!");
}
}
void Sampler::divide_samples(size_t target_sample_count, const std::vector<std::pair<int32_t, int32_t>> &samples)
{
// Initialize indicies lookup and make 1 split with entire sample range.
indicies.resize(samples.size());
for (size_t i = 0; i < samples.size(); ++i) {
indicies[i] = i;
}
splits.reserve(2);
splits.push_back(0);
splits.push_back(samples.size());
size_t divisions = std::ceil(std::sqrt(target_sample_count) / 2.);
if (divisions == 0) {
throw std::runtime_error("Math failure, unreachable!");
}
if (divisions > samples.size()) {
// Handle cases where there are few samples.
return;
}
// Recursively split samples first 50% / 50% in x direction, and then
// 50% / 50% in y direction. Repeat until the bucket is smaller than
// kMinSplit or the samples have been divided `divisions` times.
std::vector<size_t> new_splits;
for (size_t division_count = 0; division_count < divisions; ++division_count) {
new_splits.clear();
new_splits.push_back(0);
for (size_t i = 0; i < splits.size() - 1; ++i) {
size_t split_begin = splits.at(i);
size_t split_end = splits.at(i + 1);
if (split_end > indicies.size()) {
throw std::runtime_error("split_end is not valid!");
}
if (split_begin >= split_end) {
throw std::runtime_error("Invalid split from earlier pass!");
}
std::vector<size_t>::iterator begin = indicies.begin() + split_begin;
std::vector<size_t>::iterator end = indicies.begin() + split_end;
if (std::distance(begin, end) < kMinSplit) {
add_split(&new_splits, split_begin);
continue;
}
// Try to split samples 50/50 in x direction.
size_t split = partition_x(begin, end, samples);
// Try to split samples 50/50 in y direction after the x split.
size_t split_y1 = partition_y(begin, begin + split, samples);
size_t split_y2 = partition_y(begin + split, end, samples);
// Because the y2 split starts at split, add it here.
split_y2 += split;
add_split(&new_splits, split_begin);
add_split(&new_splits, split_begin + split_y1);
add_split(&new_splits, split_begin + split);
add_split(&new_splits, split_begin + split_y2);
}
add_split(&new_splits, samples.size());
if (new_splits.front() != 0) {
throw std::runtime_error("Split must start at 0");
}
if (new_splits.back() != samples.size()) {
throw std::runtime_error("Split must end at last element");
}
for (size_t i = 0; i < new_splits.size() - 1; ++i) {
if (new_splits[i] >= new_splits[i + 1]) {
throw std::runtime_error("Split indicies must be increasing");
}
}
std::swap(splits, new_splits);
}
}
NEXTPNR_NAMESPACE_END
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