factor/vm/mark_bits.hpp

156 lines
4.6 KiB
C++

namespace factor {
const int mark_bits_granularity = sizeof(cell) * 8;
const int mark_bits_mask = sizeof(cell) * 8 - 1;
struct mark_bits {
cell size;
cell start;
cell bits_size;
cell* marked;
cell* forwarding;
void clear_mark_bits() { memset(marked, 0, bits_size * sizeof(cell)); }
void clear_forwarding() { memset(forwarding, 0, bits_size * sizeof(cell)); }
mark_bits(cell size, cell start)
: size(size),
start(start),
bits_size(size / data_alignment / mark_bits_granularity),
marked(new cell[bits_size]),
forwarding(new cell[bits_size]) {
clear_mark_bits();
clear_forwarding();
}
~mark_bits() {
delete[] marked;
marked = nullptr;
delete[] forwarding;
forwarding = nullptr;
}
cell block_line(cell address) {
return (address - start) / data_alignment;
}
cell line_block(cell line) {
return line * data_alignment + start;
}
std::pair<cell, cell> bitmap_deref(const cell address) {
cell line_number = block_line(address);
cell word_index = (line_number / mark_bits_granularity);
cell word_shift = (line_number & mark_bits_mask);
return std::make_pair(word_index, word_shift);
}
bool bitmap_elt(cell* bits, const cell address) {
std::pair<cell, cell> position = bitmap_deref(address);
return (bits[position.first] & ((cell)1 << position.second)) != 0;
}
void set_bitmap_range(cell* bits, const cell address, const cell size) {
std::pair<cell, cell> start = bitmap_deref(address);
std::pair<cell, cell> end = bitmap_deref(address + size);
cell start_mask = ((cell)1 << start.second) - 1;
cell end_mask = ((cell)1 << end.second) - 1;
if (start.first == end.first)
bits[start.first] |= start_mask ^ end_mask;
else {
FACTOR_ASSERT(start.first < bits_size);
bits[start.first] |= ~start_mask;
for (cell index = start.first + 1; index < end.first; index++)
bits[index] = (cell)-1;
if (end_mask != 0) {
FACTOR_ASSERT(end.first < bits_size);
bits[end.first] |= end_mask;
}
}
}
bool marked_p(const cell address) { return bitmap_elt(marked, address); }
void set_marked_p(const cell address, const cell size) {
set_bitmap_range(marked, address, size);
}
// The eventual destination of a block after compaction is just the number
// of marked blocks before it. Live blocks must be marked on entry.
void compute_forwarding() {
cell accum = 0;
for (cell index = 0; index < bits_size; index++) {
forwarding[index] = accum;
accum += popcount(marked[index]);
}
}
// We have the popcount for every mark_bits_granularity entries; look
// up and compute the rest
cell forward_block(const cell original) {
FACTOR_ASSERT(marked_p(original));
std::pair<cell, cell> position = bitmap_deref(original);
cell offset = original & (data_alignment - 1);
cell approx_popcount = forwarding[position.first];
cell mask = ((cell)1 << position.second) - 1;
cell new_line_number =
approx_popcount + popcount(marked[position.first] & mask);
cell new_block = line_block(new_line_number) + offset;
FACTOR_ASSERT(new_block <= original);
return new_block;
}
cell next_unmarked_block_after(const cell original) {
std::pair<cell, cell> position = bitmap_deref(original);
cell bit_index = position.second;
for (cell index = position.first; index < bits_size; index++) {
cell mask = ((fixnum)marked[index] >> bit_index);
if (~mask) {
// Found an unmarked block on this page. Stop, it's hammer time
cell clear_bit = rightmost_clear_bit(mask);
return line_block(index * mark_bits_granularity + bit_index +
clear_bit);
}
// No unmarked blocks on this page. Keep looking
bit_index = 0;
}
// No unmarked blocks were found
return this->start + this->size;
}
cell next_marked_block_after(const cell original) {
std::pair<cell, cell> position = bitmap_deref(original);
cell bit_index = position.second;
for (cell index = position.first; index < bits_size; index++) {
cell mask = (marked[index] >> bit_index);
if (mask) {
// Found an marked block on this page. Stop, it's hammer time
cell set_bit = rightmost_set_bit(mask);
return line_block(index * mark_bits_granularity + bit_index + set_bit);
}
// No marked blocks on this page. Keep looking
bit_index = 0;
}
// No marked blocks were found
return this->start + this->size;
}
cell unmarked_block_size(cell original) {
cell next_marked = next_marked_block_after(original);
return next_marked - original;
}
};
}