fanlusky
80b1fc42a1
词格原先的整句打分是一份没校准过的启发式 unigram，质量很差。这里内嵌 libime 在用的 kenlm 查询子集，改由它的三元模型 sc.lm 来打路径分。 - engine/ngram 只编 kenlm 的 query / trie-build 路径。不定义 WITH_THREADS， parallel_read.cc 因此退化成串行实现，整个子集零 Boost 依赖。 KENLM_MAX_ORDER=3 必须与建模阶数一致，改它等于读不懂已发布的模型文件。 - ngram::LanguageModel 是唯一 include kenlm 头文件的地方，对外只给出一个纯 std 的头，_HAS_AUTO_PTR_ETC 和 kenlm 的 include 目录都保持 PRIVATE。 - shared_language_model 按资源路径共享一份 mmap。kenlm 的查询是只读的且把 上下文放在调用方的 State 里，所以并发会话不需要额外加锁。 - 模型缺失时 valid() 为假，词格退回原来的启发式打分：整句候选只是变差，不会 停止工作。测试覆盖了缺模型降级与按路径共享。 - 出货的 ARPA 不带 <s>/</s>，所以解码从 null_state() 起算而非 begin_state()。 kenlm 是上游副本，不重排版、不进 clang-format，其 LGPL-2.1+ 与 BSD 例外清单 已补进 THIRD_PARTY_NOTICES.txt。googlepinyinime 那条 Fallback 整句路径不变。
94 lines
3.7 KiB
C++
94 lines
3.7 KiB
C++
/* Quantize into bins of equal size as described in
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* M. Federico and N. Bertoldi. 2006. How many bits are needed
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* to store probabilities for phrase-based translation? In Proc.
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* of the Workshop on Statistical Machine Translation, pages
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* 94–101, New York City, June. Association for Computa-
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* tional Linguistics.
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*/
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#include "quantize.hh"
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#include "binary_format.hh"
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#include "lm_exception.hh"
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#include "../util/file.hh"
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#include <algorithm>
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#include <numeric>
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namespace lm {
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namespace ngram {
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namespace {
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void MakeBins(std::vector<float> &values, float *centers, uint32_t bins) {
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std::sort(values.begin(), values.end());
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std::vector<float>::const_iterator start = values.begin(), finish;
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for (uint32_t i = 0; i < bins; ++i, ++centers, start = finish) {
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finish = values.begin() + ((values.size() * static_cast<uint64_t>(i + 1)) / bins);
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if (finish == start) {
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// zero length bucket.
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*centers = i ? *(centers - 1) : -std::numeric_limits<float>::infinity();
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} else {
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*centers = std::accumulate(start, finish, 0.0) / static_cast<float>(finish - start);
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}
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}
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}
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const char kSeparatelyQuantizeVersion = 2;
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} // namespace
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void SeparatelyQuantize::UpdateConfigFromBinary(const BinaryFormat &file, uint64_t offset, Config &config) {
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unsigned char buffer[3];
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file.ReadForConfig(buffer, 3, offset);
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char version = buffer[0];
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config.prob_bits = buffer[1];
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config.backoff_bits = buffer[2];
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if (version != kSeparatelyQuantizeVersion) UTIL_THROW(FormatLoadException, "This file has quantization version " << (unsigned)version << " but the code expects version " << (unsigned)kSeparatelyQuantizeVersion);
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}
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void SeparatelyQuantize::SetupMemory(void *base, unsigned char order, const Config &config) {
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prob_bits_ = config.prob_bits;
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backoff_bits_ = config.backoff_bits;
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// We need the reserved values.
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if (config.prob_bits == 0) UTIL_THROW(ConfigException, "You can't quantize probability to zero");
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if (config.backoff_bits == 0) UTIL_THROW(ConfigException, "You can't quantize backoff to zero");
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if (config.prob_bits > 25) UTIL_THROW(ConfigException, "For efficiency reasons, quantizing probability supports at most 25 bits. Currently you have requested " << static_cast<unsigned>(config.prob_bits) << " bits.");
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if (config.backoff_bits > 25) UTIL_THROW(ConfigException, "For efficiency reasons, quantizing backoff supports at most 25 bits. Currently you have requested " << static_cast<unsigned>(config.backoff_bits) << " bits.");
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// Reserve 8 byte header for bit counts.
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actual_base_ = static_cast<uint8_t*>(base);
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float *start = reinterpret_cast<float*>(actual_base_ + 8);
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for (unsigned char i = 0; i < order - 2; ++i) {
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tables_[i][0] = Bins(prob_bits_, start);
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start += (1ULL << prob_bits_);
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tables_[i][1] = Bins(backoff_bits_, start);
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start += (1ULL << backoff_bits_);
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}
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longest_ = tables_[order - 2][0] = Bins(prob_bits_, start);
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}
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void SeparatelyQuantize::Train(uint8_t order, std::vector<float> &prob, std::vector<float> &backoff) {
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TrainProb(order, prob);
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// Backoff
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float *centers = tables_[order - 2][1].Populate();
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*(centers++) = kNoExtensionBackoff;
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*(centers++) = kExtensionBackoff;
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MakeBins(backoff, centers, (1ULL << backoff_bits_) - 2);
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}
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void SeparatelyQuantize::TrainProb(uint8_t order, std::vector<float> &prob) {
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float *centers = tables_[order - 2][0].Populate();
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MakeBins(prob, centers, (1ULL << prob_bits_));
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}
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void SeparatelyQuantize::FinishedLoading(const Config &config) {
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uint8_t *actual_base = actual_base_;
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*(actual_base++) = kSeparatelyQuantizeVersion; // version
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*(actual_base++) = config.prob_bits;
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*(actual_base++) = config.backoff_bits;
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}
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} // namespace ngram
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} // namespace lm
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