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Get rid of idxbits

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Use indexSpan instead. This could be a teoretical
slwo down becuae we repalce some shifts by divide
and modulo, but this should not be measurable and
instead the code is more understandable now. This
is a big plus becuase this part of code is complex.
This commit is contained in:
Marco Costalba 2016-05-14 08:08:47 +02:00
parent c0476e12db
commit 04f94b1538
1 changed files with 14 additions and 14 deletions
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28
src/syzygy/tbprobe.cpp
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@ -65,8 +65,8 @@ static_assert(sizeof(SparseEntry) == 6, "SparseEntry must be 6 bytes");
struct PairsData {
int flags;
size_t sizeofBlock; // Block size in bytes
int idxbits; // Every 1 << idxbits index values there is a blockEntryIndex[] entry
size_t sizeofBlock; // Block size in bytes
size_t span; // About every span values there is a SparseIndex[] entry
int real_num_blocks;
int num_blocks;
int max_len;
@ -75,7 +75,7 @@ struct PairsData {
uint8_t* sympat;
uint16_t* blockLenghts; // Number of stored positions (minus one) for each block
SparseEntry* sparseIndex; // Partial indices into blockLenghts[]
int num_indices; // Size of SparseIndex[] table
size_t sparseIndexSize; // Size of SparseIndex[] table
uint8_t* data; // Start of Huffman compressed data
std::vector<uint64_t> base;
std::vector<uint8_t> symlen;
@ -488,10 +488,10 @@ int decompress_pairs(PairsData* d, uint64_t idx)
// that stores the blockLenghts[] index and the offset within that block of the value
// with index N(k), where:
//
// N(k) = k * (1 << d->idxbits) + (1 << (d->idxbits - 1)) (1)
// N(k) = k * d->span + d->span / 2 (1)
// First step is to get the 'k' of the N(k) nearest to our idx, using defintion (1)
uint32_t k = (uint32_t)(idx >> d->idxbits);
uint32_t k = idx / d->span;
// Then we read the corresponding SparseIndex[] entry
uint32_t block = number<uint32_t, LittleEndian>(&d->sparseIndex[k].block);
@ -499,10 +499,10 @@ int decompress_pairs(PairsData* d, uint64_t idx)
// Now compute the difference idx - N(k). From defintion of k we know that
//
// idx = k * (1 << d->idxbits) + (idx & ((1ULL << d->idxbits) - 1)) (2)
// idx = k * d->span + idx % d->span (2)
//
// So, from (2) and (1) we can compute idx - N(K):
int diff = (idx & ((1ULL << d->idxbits) - 1)) - (1 << (d->idxbits - 1));
// So we can compute idx - N(K):
int diff = idx % d->span - d->span / 2;
// Sum to idxOffset to find the offset corresponding to our idx
idxOffset += diff;
@ -919,15 +919,15 @@ uint8_t* set_sizes(PairsData* d, uint8_t* data, uint64_t tb_size)
d->flags = *data++;
if (d->flags & TBFlag::SingleValue) {
d->idxbits = d->real_num_blocks =
d->num_blocks = d->num_indices = 0; // Broken MSVC zero-init
d->real_num_blocks = d->span =
d->num_blocks = d->sparseIndexSize = 0; // Broken MSVC zero-init
d->min_len = *data++;
return data;
}
d->sizeofBlock = 1 << *data++;
d->idxbits = *data++;
d->num_indices = (tb_size + (1ULL << d->idxbits) - 1) >> d->idxbits; // Divide and round upward, like ceil()
d->sizeofBlock = 1ULL << *data++;
d->span = 1ULL << *data++;
d->sparseIndexSize = (tb_size + d->span - 1) / d->span; // Round up
d->num_blocks = number<uint8_t, LittleEndian>(data++);
d->real_num_blocks = number<uint32_t, LittleEndian>(data); data += sizeof(uint32_t);
d->num_blocks += d->real_num_blocks;
@ -1034,7 +1034,7 @@ void do_init(Entry& e, T& p, uint8_t* data)
for (File f = FILE_A; f <= maxFile; ++f)
for (int k = 0; k <= split; k++) {
(d = item(p, k, f).precomp)->sparseIndex = (SparseEntry*)data;
data += d->num_indices * sizeof(SparseEntry) ;
data += d->sparseIndexSize * sizeof(SparseEntry) ;
}
for (File f = FILE_A; f <= maxFile; ++f)