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/* SPDX-License-Identifier: GPL-2.0-or-later
* Copyright 2021 Blender Foundation.
*/
/** \file
* \ingroup eevee
*
* Allocators that may be moved to BLI at some point.
*/
#pragma once
#include "BLI_math_bits.h"
#include "BLI_vector.hh"
namespace blender::eevee {
/**
* Allow allocation and deletion of elements without reordering.
* Useful to keed valid indices to items inside this allocator.
* Type T need to implement the free_resources() method.
*/
template<typename T> class IndexedAllocator {
private:
Vector<T> items_;
/** Bitmap of used items. Make search of unused slot faster. */
Vector<uint32_t> unused_;
/** First unused batch of items in the vector for fast reallocating. */
int64_t unused_first_ = LONG_MAX;
/** Unused item count in the vector for fast reallocating. */
int64_t unused_count_ = 0;
public:
int64_t alloc(T &&value)
{
if (unused_count_ > 0) {
/* Reclaim unused slot. */
int64_t index = unused_first_;
items_[index] = std::move(value);
set_slot_used(index);
unused_count_ -= 1;
unused_first_ = first_unused_slot_get();
return index;
}
/* Not enough place, grow the vector. */
int64_t index = items_.append_and_get_index(value);
int64_t size_needed = (index + 32) / 32;
int64_t size_old = unused_.size();
unused_.resize(size_needed);
if (size_old < size_needed) {
for (auto i : IndexRange(size_old, size_needed - size_old)) {
/* Used by default. */
unused_[i] = 0;
}
}
set_slot_used(index);
return index;
}
void free(int64_t index)
{
unused_count_ += 1;
if (index < unused_first_) {
unused_first_ = index;
}
set_slot_unused(index);
is_slot_unused(index);
items_[index].free_resources();
}
/* Pruned unused shadows at the end of the vector. */
void resize()
{
while (items_.size() > 0 && is_slot_unused(items_.size() - 1)) {
set_slot_used(items_.size() - 1);
items_.remove_last();
unused_count_--;
}
if (unused_first_ >= items_.size()) {
/* First unused has been pruned. */
unused_first_ = first_unused_slot_get();
}
}
int64_t size() const
{
return items_.size() - unused_count_;
}
class Iterator {
public:
using iterator_category = std::forward_iterator_tag;
using value_type = T;
using pointer = const T *;
using reference = const T &;
using difference_type = std::ptrdiff_t;
private:
IndexedAllocator &allocator_;
int64_t current_;
public:
constexpr explicit Iterator(IndexedAllocator &allocator, int64_t current)
: allocator_(allocator), current_(current)
{
}
constexpr Iterator &operator++()
{
current_++;
while ((current_ < allocator_.items_.size()) && allocator_.is_slot_unused(current_)) {
current_++;
}
return *this;
}
constexpr Iterator operator++(int) const
{
Iterator iterator = *this;
++*this;
return iterator;
}
constexpr friend bool operator!=(const Iterator &a, const Iterator &b)
{
return a.current_ != b.current_;
}
T &operator*()
{
BLI_assert(allocator_.is_slot_unused(current_) == false);
return allocator_[current_];
}
};
constexpr Iterator begin()
{
int64_t first_used = first_used_slot_get();
if (first_used == LONG_MAX) {
/* Will produce no iteration. */
first_used = items_.size();
}
return Iterator(*this, first_used);
}
constexpr Iterator end()
{
return Iterator(*this, items_.size());
}
const T &operator[](int64_t index) const
{
BLI_assert(is_slot_unused(index) == false);
return items_[index];
}
T &operator[](int64_t index)
{
BLI_assert(is_slot_unused(index) == false);
return items_[index];
}
private:
int64_t first_unused_slot_get(void) const
{
if (unused_count_ > 0) {
for (auto i : IndexRange(unused_.size())) {
if (unused_[i] != 0) {
return i * 32 + bitscan_forward_uint(unused_[i]);
}
}
}
return LONG_MAX;
}
int64_t first_used_slot_get(void) const
{
if (unused_count_ < items_.size()) {
for (auto i : IndexRange(unused_.size())) {
if (~unused_[i] != 0) {
return i * 32 + bitscan_forward_uint(~unused_[i]);
}
}
}
return LONG_MAX;
}
bool is_slot_unused(int64_t index) const
{
return (unused_[index / 32] & (1u << uint32_t(index % 32))) != 0;
}
void set_slot_unused(int64_t index)
{
SET_FLAG_FROM_TEST(unused_[index / 32], true, (1u << uint32_t(index % 32)));
}
void set_slot_used(int64_t index)
{
SET_FLAG_FROM_TEST(unused_[index / 32], false, (1u << uint32_t(index % 32)));
}
};
} // namespace blender::eevee
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