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/* Simple implementation of
* @inproceedings{bhikshacompression,
* author={Bhiksha Raj and Ed Whittaker},
* year={2003},
* title={Lossless Compression of Language Model Structure and Word Identifiers},
* booktitle={Proceedings of IEEE International Conference on Acoustics, Speech and Signal Processing},
* pages={388--391},
* }
*
* Currently only used for next pointers.
*/
#ifndef LM_BHIKSHA__
#define LM_BHIKSHA__
#include <stdint.h>
#include <assert.h>
#include "lm/model_type.hh"
#include "lm/trie.hh"
#include "util/bit_packing.hh"
#include "util/sorted_uniform.hh"
namespace lm {
namespace ngram {
struct Config;
namespace trie {
class DontBhiksha {
public:
static const ModelType kModelTypeAdd = static_cast<ModelType>(0);
static void UpdateConfigFromBinary(int /*fd*/, Config &/*config*/) {}
static std::size_t Size(uint64_t /*max_offset*/, uint64_t /*max_next*/, const Config &/*config*/) { return 0; }
static uint8_t InlineBits(uint64_t /*max_offset*/, uint64_t max_next, const Config &/*config*/) {
return util::RequiredBits(max_next);
}
DontBhiksha(const void *base, uint64_t max_offset, uint64_t max_next, const Config &config);
void ReadNext(const void *base, uint64_t bit_offset, uint64_t /*index*/, uint8_t total_bits, NodeRange &out) const {
out.begin = util::ReadInt57(base, bit_offset, next_.bits, next_.mask);
out.end = util::ReadInt57(base, bit_offset + total_bits, next_.bits, next_.mask);
//assert(out.end >= out.begin);
}
void WriteNext(void *base, uint64_t bit_offset, uint64_t /*index*/, uint64_t value) {
util::WriteInt57(base, bit_offset, next_.bits, value);
}
void FinishedLoading(const Config &/*config*/) {}
void LoadedBinary() {}
uint8_t InlineBits() const { return next_.bits; }
private:
util::BitsMask next_;
};
class ArrayBhiksha {
public:
static const ModelType kModelTypeAdd = kArrayAdd;
static void UpdateConfigFromBinary(int fd, Config &config);
static std::size_t Size(uint64_t max_offset, uint64_t max_next, const Config &config);
static uint8_t InlineBits(uint64_t max_offset, uint64_t max_next, const Config &config);
ArrayBhiksha(void *base, uint64_t max_offset, uint64_t max_value, const Config &config);
void ReadNext(const void *base, uint64_t bit_offset, uint64_t index, uint8_t total_bits, NodeRange &out) const {
const uint64_t *begin_it = util::BinaryBelow(util::IdentityAccessor<uint64_t>(), offset_begin_, offset_end_, index);
const uint64_t *end_it;
for (end_it = begin_it; (end_it < offset_end_) && (*end_it <= index + 1); ++end_it) {}
--end_it;
out.begin = ((begin_it - offset_begin_) << next_inline_.bits) |
util::ReadInt57(base, bit_offset, next_inline_.bits, next_inline_.mask);
out.end = ((end_it - offset_begin_) << next_inline_.bits) |
util::ReadInt57(base, bit_offset + total_bits, next_inline_.bits, next_inline_.mask);
//assert(out.end >= out.begin);
}
void WriteNext(void *base, uint64_t bit_offset, uint64_t index, uint64_t value) {
uint64_t encode = value >> next_inline_.bits;
for (; write_to_ <= offset_begin_ + encode; ++write_to_) *write_to_ = index;
util::WriteInt57(base, bit_offset, next_inline_.bits, value & next_inline_.mask);
}
void FinishedLoading(const Config &config);
void LoadedBinary();
uint8_t InlineBits() const { return next_inline_.bits; }
private:
const util::BitsMask next_inline_;
const uint64_t *const offset_begin_;
const uint64_t *const offset_end_;
uint64_t *write_to_;
void *original_base_;
};
} // namespace trie
} // namespace ngram
} // namespace lm
#endif // LM_BHIKSHA__
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