factor/vm/mark_bits.hpp

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C++
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namespace factor
{
const int block_granularity = 16;
const int forwarding_granularity = 64;
template<typename Block> struct mark_bits {
cell size;
cell start;
cell bits_size;
u64 *marked;
cell *forwarding;
void clear_mark_bits()
{
memset(marked,0,bits_size * sizeof(u64));
}
void clear_forwarding()
{
memset(forwarding,0,bits_size * sizeof(cell));
}
explicit mark_bits(cell size_, cell start_) :
size(size_),
start(start_),
bits_size(size / block_granularity / forwarding_granularity),
marked(new u64[bits_size]),
forwarding(new cell[bits_size])
{
clear_mark_bits();
clear_forwarding();
}
~mark_bits()
{
delete[] marked;
marked = NULL;
delete[] forwarding;
forwarding = NULL;
}
cell block_line(Block *address)
{
return (((cell)address - start) / block_granularity);
}
Block *line_block(cell line)
{
return (Block *)(line * block_granularity + start);
}
std::pair<cell,cell> bitmap_deref(Block *address)
{
cell line_number = block_line(address);
cell word_index = (line_number >> 6);
cell word_shift = (line_number & 63);
return std::make_pair(word_index,word_shift);
}
bool bitmap_elt(u64 *bits, Block *address)
{
std::pair<cell,cell> pair = bitmap_deref(address);
return (bits[pair.first] & ((u64)1 << pair.second)) != 0;
}
Block *next_block_after(Block *block)
{
return (Block *)((cell)block + block->size());
}
void set_bitmap_range(u64 *bits, Block *address)
{
std::pair<cell,cell> start = bitmap_deref(address);
std::pair<cell,cell> end = bitmap_deref(next_block_after(address));
u64 start_mask = ((u64)1 << start.second) - 1;
u64 end_mask = ((u64)1 << end.second) - 1;
if(start.first == end.first)
bits[start.first] |= start_mask ^ end_mask;
else
{
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#ifdef FACTOR_DEBUG
assert(start.first < bits_size);
#endif
bits[start.first] |= ~start_mask;
for(cell index = start.first + 1; index < end.first; index++)
bits[index] = (u64)-1;
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if(end_mask != 0)
{
#ifdef FACTOR_DEBUG
assert(end.first < bits_size);
#endif
bits[end.first] |= end_mask;
}
}
}
bool marked_p(Block *address)
{
return bitmap_elt(marked,address);
}
void set_marked_p(Block *address)
{
set_bitmap_range(marked,address);
}
/* From http://chessprogramming.wikispaces.com/Population+Count */
cell popcount(u64 x)
{
u64 k1 = 0x5555555555555555ll;
u64 k2 = 0x3333333333333333ll;
u64 k4 = 0x0f0f0f0f0f0f0f0fll;
u64 kf = 0x0101010101010101ll;
x = x - ((x >> 1) & k1); // put count of each 2 bits into those 2 bits
x = (x & k2) + ((x >> 2) & k2); // put count of each 4 bits into those 4 bits
x = (x + (x >> 4)) & k4 ; // put count of each 8 bits into those 8 bits
x = (x * kf) >> 56; // returns 8 most significant bits of x + (x<<8) + (x<<16) + (x<<24) + ...
return (cell)x;
}
/* 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 64 entries; look up and compute the rest */
Block *forward_block(Block *original)
{
std::pair<cell,cell> pair = bitmap_deref(original);
cell approx_popcount = forwarding[pair.first];
u64 mask = ((u64)1 << pair.second) - 1;
cell new_line_number = approx_popcount + popcount(marked[pair.first] & mask);
return line_block(new_line_number);
}
};
template<typename Block, typename Iterator> struct heap_compactor {
mark_bits<Block> *state;
char *address;
Iterator &iter;
explicit heap_compactor(mark_bits<Block> *state_, Block *address_, Iterator &iter_) :
state(state_), address((char *)address_), iter(iter_) {}
void operator()(Block *block, cell size)
{
if(this->state->marked_p(block))
{
memmove(address,block,size);
iter((Block *)address,size);
address += size;
}
}
};
}