mirror of
https://github.com/moses-smt/mosesdecoder.git
synced 2024-12-27 14:05:29 +03:00
96 lines
3.6 KiB
C++
96 lines
3.6 KiB
C++
#include "lm/bhiksha.hh"
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#include "lm/config.hh"
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#include "util/file.hh"
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#include "util/exception.hh"
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#include <limits>
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namespace lm {
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namespace ngram {
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namespace trie {
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DontBhiksha::DontBhiksha(const void * /*base*/, uint64_t /*max_offset*/, uint64_t max_next, const Config &/*config*/) :
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next_(util::BitsMask::ByMax(max_next)) {}
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const uint8_t kArrayBhikshaVersion = 0;
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// TODO: put this in binary file header instead when I change the binary file format again.
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void ArrayBhiksha::UpdateConfigFromBinary(int fd, Config &config) {
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uint8_t version;
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uint8_t configured_bits;
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util::ReadOrThrow(fd, &version, 1);
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util::ReadOrThrow(fd, &configured_bits, 1);
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if (version != kArrayBhikshaVersion) UTIL_THROW(FormatLoadException, "This file has sorted array compression version " << (unsigned) version << " but the code expects version " << (unsigned)kArrayBhikshaVersion);
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config.pointer_bhiksha_bits = configured_bits;
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}
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namespace {
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// Find argmin_{chopped \in [0, RequiredBits(max_next)]} ChoppedDelta(max_offset)
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uint8_t ChopBits(uint64_t max_offset, uint64_t max_next, const Config &config) {
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uint8_t required = util::RequiredBits(max_next);
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uint8_t best_chop = 0;
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int64_t lowest_change = std::numeric_limits<int64_t>::max();
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// There are probably faster ways but I don't care because this is only done once per order at construction time.
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for (uint8_t chop = 0; chop <= std::min(required, config.pointer_bhiksha_bits); ++chop) {
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int64_t change = (max_next >> (required - chop)) * 64 /* table cost in bits */
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- max_offset * static_cast<int64_t>(chop); /* savings in bits*/
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if (change < lowest_change) {
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lowest_change = change;
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best_chop = chop;
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}
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}
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return best_chop;
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}
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std::size_t ArrayCount(uint64_t max_offset, uint64_t max_next, const Config &config) {
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uint8_t required = util::RequiredBits(max_next);
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uint8_t chopping = ChopBits(max_offset, max_next, config);
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return (max_next >> (required - chopping)) + 1 /* we store 0 too */;
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}
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} // namespace
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uint64_t ArrayBhiksha::Size(uint64_t max_offset, uint64_t max_next, const Config &config) {
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return sizeof(uint64_t) * (1 /* header */ + ArrayCount(max_offset, max_next, config)) + 7 /* 8-byte alignment */;
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}
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uint8_t ArrayBhiksha::InlineBits(uint64_t max_offset, uint64_t max_next, const Config &config) {
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return util::RequiredBits(max_next) - ChopBits(max_offset, max_next, config);
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}
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namespace {
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void *AlignTo8(void *from) {
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uint8_t *val = reinterpret_cast<uint8_t*>(from);
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std::size_t remainder = reinterpret_cast<std::size_t>(val) & 7;
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if (!remainder) return val;
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return val + 8 - remainder;
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}
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} // namespace
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ArrayBhiksha::ArrayBhiksha(void *base, uint64_t max_offset, uint64_t max_next, const Config &config)
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: next_inline_(util::BitsMask::ByBits(InlineBits(max_offset, max_next, config))),
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offset_begin_(reinterpret_cast<const uint64_t*>(AlignTo8(base)) + 1 /* 8-byte header */),
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offset_end_(offset_begin_ + ArrayCount(max_offset, max_next, config)),
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write_to_(reinterpret_cast<uint64_t*>(AlignTo8(base)) + 1 /* 8-byte header */ + 1 /* first entry is 0 */),
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original_base_(base) {}
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void ArrayBhiksha::FinishedLoading(const Config &config) {
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// *offset_begin_ = 0 but without a const_cast.
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*(write_to_ - (write_to_ - offset_begin_)) = 0;
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if (write_to_ != offset_end_) UTIL_THROW(util::Exception, "Did not get all the array entries that were expected.");
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uint8_t *head_write = reinterpret_cast<uint8_t*>(original_base_);
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*(head_write++) = kArrayBhikshaVersion;
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*(head_write++) = config.pointer_bhiksha_bits;
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}
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void ArrayBhiksha::LoadedBinary() {
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}
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} // namespace trie
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} // namespace ngram
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} // namespace lm
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