unicharcompress.cpp

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// File:        unicharcompress.cpp
// Description: Unicode re-encoding using a sequence of smaller numbers in
//              place of a single large code for CJK, similarly for Indic,
//              and dissection of ligatures for other scripts.
// Author:      Ray Smith
// Created:     Wed Mar 04 14:45:01 PST 2015
//
// (C) Copyright 2015, Google Inc.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

#include "unicharcompress.h"
#include "tprintf.h"

namespace tesseract {

// String used to represent the null_id in direct_set.
const char* kNullChar = "<nul>";

// Local struct used only for processing the radical-stroke table.
struct RadicalStroke {
  RadicalStroke() : num_strokes(0) {}
  RadicalStroke(const STRING& r, int s) : radical(r), num_strokes(s) {}

  bool operator==(const RadicalStroke& other) const {
    return radical == other.radical && num_strokes == other.num_strokes;
  }

  // The radical is encoded as a string because its format is of an int with
  // an optional ' mark to indicate a simplified shape. To treat these as
  // distinct, we use a string and a UNICHARSET to do the integer mapping.
  STRING radical;
  // The number of strokes we treat as dense and just take the face value from
  // the table.
  int num_strokes;
};

// Hash functor for RadicalStroke.
struct RadicalStrokedHash {
  size_t operator()(const RadicalStroke& rs) const {
    size_t result = rs.num_strokes;
    for (int i = 0; i < rs.radical.length(); ++i) {
      result ^= rs.radical[i] << (6 * i + 8);
    }
    return result;
  }
};

// A hash map to convert unicodes to radical,stroke pair.
typedef std::unordered_map<int, RadicalStroke> RSMap;
// A hash map to count occurrences of each radical,stroke pair.
typedef std::unordered_map<RadicalStroke, int, RadicalStrokedHash> RSCounts;

// Helper function builds the RSMap from the radical-stroke file, which has
// already been read into a STRING. Returns false on error.
// The radical_stroke_table is non-const because it gets split and the caller
// is unlikely to want to use it again.
static bool DecodeRadicalStrokeTable(STRING* radical_stroke_table,
                                     RSMap* radical_map) {
  GenericVector<STRING> lines;
  radical_stroke_table->split('\n', &lines);
  for (int i = 0; i < lines.size(); ++i) {
    if (lines[i].length() == 0 || lines[i][0] == '#') continue;
    int unicode, radical, strokes;
    STRING str_radical;
    if (sscanf(lines[i].string(), "%x\t%d.%d", &unicode, &radical, &strokes) ==
        3) {
      str_radical.add_str_int("", radical);
    } else if (sscanf(lines[i].string(), "%x\t%d'.%d", &unicode, &radical,
                      &strokes) == 3) {
      str_radical.add_str_int("'", radical);
    } else {
      tprintf("Invalid format in radical stroke table at line %d: %s\n", i,
              lines[i].string());
      return false;
    }
    (*radical_map)[unicode] = RadicalStroke(str_radical, strokes);
  }
  return true;
}

UnicharCompress::UnicharCompress() : code_range_(0) {}
UnicharCompress::UnicharCompress(const UnicharCompress& src) { *this = src; }
UnicharCompress::~UnicharCompress() { Cleanup(); }
UnicharCompress& UnicharCompress::operator=(const UnicharCompress& src) {
  Cleanup();
  encoder_ = src.encoder_;
  code_range_ = src.code_range_;
  SetupDecoder();
  return *this;
}

// Computes the encoding for the given unicharset. It is a requirement that
// the file training/langdata/radical-stroke.txt have been read into the
// input string radical_stroke_table.
// Returns false if the encoding cannot be constructed.
bool UnicharCompress::ComputeEncoding(const UNICHARSET& unicharset, int null_id,
                                      STRING* radical_stroke_table) {
  RSMap radical_map;
  if (!DecodeRadicalStrokeTable(radical_stroke_table, &radical_map))
    return false;
  encoder_.clear();
  UNICHARSET direct_set;
  UNICHARSET radicals;
  // To avoid unused codes, clear the special codes from the unicharsets.
  direct_set.clear();
  radicals.clear();
  // Always keep space as 0;
  direct_set.unichar_insert(" ");
  // Null char is next if we have one.
  if (null_id >= 0) {
    direct_set.unichar_insert(kNullChar);
  }
  RSCounts radical_counts;
  // In the initial map, codes [0, unicharset.size()) are
  // reserved for non-han/hangul sequences of 1 or more unicodes.
  int hangul_offset = unicharset.size();
  // Hangul takes the next range [hangul_offset, hangul_offset + kTotalJamos).
  const int kTotalJamos = kLCount + kVCount + kTCount;
  // Han takes the codes beyond hangul_offset + kTotalJamos. Since it is hard
  // to measure the number of radicals and strokes, initially we use the same
  // code range for all 3 Han code positions, and fix them after.
  int han_offset = hangul_offset + kTotalJamos;
  int max_num_strokes = -1;
  for (int u = 0; u <= unicharset.size(); ++u) {
    bool self_normalized = false;
    // We special-case allow null_id to be equal to unicharset.size() in case
    // there is no space in unicharset for it.
    if (u == unicharset.size()) {
      if (u == null_id) {
        self_normalized = true;
      } else {
        break;  // Finished.
      }
    } else {
      self_normalized = strcmp(unicharset.id_to_unichar(u),
                               unicharset.get_normed_unichar(u)) == 0;
    }
    RecodedCharID code;
    // Convert to unicodes.
    GenericVector<int> unicodes;
    if (u < unicharset.size() &&
        UNICHAR::UTF8ToUnicode(unicharset.get_normed_unichar(u), &unicodes) &&
        unicodes.size() == 1) {
      // Check single unicodes for Hangul/Han and encode if so.
      int unicode = unicodes[0];
      int leading, vowel, trailing;
      auto it = radical_map.find(unicode);
      if (it != radical_map.end()) {
        // This is Han. Convert to radical, stroke, index.
        if (!radicals.contains_unichar(it->second.radical.string())) {
          radicals.unichar_insert(it->second.radical.string());
        }
        int radical = radicals.unichar_to_id(it->second.radical.string());
        int num_strokes = it->second.num_strokes;
        int num_samples = radical_counts[it->second]++;
        if (num_strokes > max_num_strokes) max_num_strokes = num_strokes;
        code.Set3(radical + han_offset, num_strokes + han_offset,
                  num_samples + han_offset);
      } else if (DecomposeHangul(unicode, &leading, &vowel, &trailing)) {
        // This is Hangul. Since we know the exact size of each part at compile
        // time, it gets the bottom set of codes.
        code.Set3(leading + hangul_offset, vowel + kLCount + hangul_offset,
                  trailing + kLCount + kVCount + hangul_offset);
      }
    }
    // If the code is still empty, it wasn't Han or Hangul.
    if (code.length() == 0) {
      // Special cases.
      if (u == UNICHAR_SPACE) {
        code.Set(0, 0);  // Space.
      } else if (u == null_id || (unicharset.has_special_codes() &&
                                  u < SPECIAL_UNICHAR_CODES_COUNT)) {
        code.Set(0, direct_set.unichar_to_id(kNullChar));
      } else {
        // Add the direct_set unichar-ids of the unicodes in sequence to the
        // code.
        for (int i = 0; i < unicodes.size(); ++i) {
          int position = code.length();
          if (position >= RecodedCharID::kMaxCodeLen) {
            tprintf("Unichar %d=%s->%s is too long to encode!!\n", u,
                    unicharset.id_to_unichar(u),
                    unicharset.get_normed_unichar(u));
            return false;
          }
          int uni = unicodes[i];
          UNICHAR unichar(uni);
          char* utf8 = unichar.utf8_str();
          if (!direct_set.contains_unichar(utf8))
            direct_set.unichar_insert(utf8);
          code.Set(position, direct_set.unichar_to_id(utf8));
          delete[] utf8;
          if (direct_set.size() > unicharset.size()) {
            // Code space got bigger!
            tprintf("Code space expanded from original unicharset!!\n");
            return false;
          }
        }
      }
    }
    code.set_self_normalized(self_normalized);
    encoder_.push_back(code);
  }
  // Now renumber Han to make all codes unique. We already added han_offset to
  // all Han. Now separate out the radical, stroke, and count codes for Han.
  // In the uniqued Han encoding, the 1st code uses the next radical_map.size()
  // values, the 2nd code uses the next max_num_strokes+1 values, and the 3rd
  // code uses the rest for the max number of duplicated radical/stroke combos.
  int num_radicals = radicals.size();
  for (int u = 0; u < unicharset.size(); ++u) {
    RecodedCharID* code = &encoder_[u];
    if ((*code)(0) >= han_offset) {
      code->Set(1, (*code)(1) + num_radicals);
      code->Set(2, (*code)(2) + num_radicals + max_num_strokes + 1);
    }
  }
  DefragmentCodeValues(null_id >= 0 ? 1 : -1);
  SetupDecoder();
  return true;
}

// Sets up an encoder that doesn't change the unichars at all, so it just
// passes them through unchanged.
void UnicharCompress::SetupPassThrough(const UNICHARSET& unicharset) {
  GenericVector<RecodedCharID> codes;
  for (int u = 0; u < unicharset.size(); ++u) {
    RecodedCharID code;
    code.Set(0, u);
    codes.push_back(code);
  }
  SetupDirect(codes);
}

// Sets up an encoder directly using the given encoding vector, which maps
// unichar_ids to the given codes.
void UnicharCompress::SetupDirect(const GenericVector<RecodedCharID>& codes) {
  encoder_ = codes;
  ComputeCodeRange();
  SetupDecoder();
}

// Renumbers codes to eliminate unused values.
void UnicharCompress::DefragmentCodeValues(int encoded_null) {
  // There may not be any Hangul, but even if there is, it is possible that not
  // all codes are used. Likewise with the Han encoding, it is possible that not
  // all numbers of strokes are used.
  ComputeCodeRange();
  GenericVector<int> offsets;
  offsets.init_to_size(code_range_, 0);
  // Find which codes are used
  for (int c = 0; c < encoder_.size(); ++c) {
    const RecodedCharID& code = encoder_[c];
    for (int i = 0; i < code.length(); ++i) {
      offsets[code(i)] = 1;
    }
  }
  // Compute offsets based on code use.
  int offset = 0;
  for (int i = 0; i < offsets.size(); ++i) {
    // If not used, decrement everything above here.
    // We are moving encoded_null to the end, so it is not "used".
    if (offsets[i] == 0 || i == encoded_null) {
      --offset;
    } else {
      offsets[i] = offset;
    }
  }
  if (encoded_null >= 0) {
    // The encoded_null is moving to the end, for the benefit of TensorFlow,
    // which is offsets.size() + offsets.back().
    offsets[encoded_null] = offsets.size() + offsets.back() - encoded_null;
  }
  // Now apply the offsets.
  for (int c = 0; c < encoder_.size(); ++c) {
    RecodedCharID* code = &encoder_[c];
    for (int i = 0; i < code->length(); ++i) {
      int value = (*code)(i);
      code->Set(i, value + offsets[value]);
    }
  }
  ComputeCodeRange();
}

// Encodes a single unichar_id. Returns the length of the code, or zero if
// invalid input, and the encoding itself
int UnicharCompress::EncodeUnichar(int unichar_id, RecodedCharID* code) const {
  if (unichar_id < 0 || unichar_id >= encoder_.size()) return 0;
  *code = encoder_[unichar_id];
  return code->length();
}

// Decodes code, returning the original unichar-id, or
// INVALID_UNICHAR_ID if the input is invalid.
int UnicharCompress::DecodeUnichar(const RecodedCharID& code) const {
  int len = code.length();
  if (len <= 0 || len > RecodedCharID::kMaxCodeLen) return INVALID_UNICHAR_ID;
  auto it = decoder_.find(code);
  if (it == decoder_.end()) return INVALID_UNICHAR_ID;
  return it->second;
}

// Writes to the given file. Returns false in case of error.
bool UnicharCompress::Serialize(TFile* fp) const {
  return encoder_.SerializeClasses(fp);
}

// Reads from the given file. Returns false in case of error.
bool UnicharCompress::DeSerialize(TFile* fp) {
  if (!encoder_.DeSerializeClasses(fp)) return false;
  ComputeCodeRange();
  SetupDecoder();
  return true;
}

// Returns a STRING containing a text file that describes the encoding thus:
// <index>[,<index>]*<tab><UTF8-str><newline>
// In words, a comma-separated list of one or more indices, followed by a tab
// and the UTF-8 string that the code represents per line. Most simple scripts
// will encode a single index to a UTF8-string, but Chinese, Japanese, Korean
// and the Indic scripts will contain a many-to-many mapping.
// See the class comment above for details.
STRING UnicharCompress::GetEncodingAsString(
    const UNICHARSET& unicharset) const {
  STRING encoding;
  for (int c = 0; c < encoder_.size(); ++c) {
    const RecodedCharID& code = encoder_[c];
    if (0 < c && c < SPECIAL_UNICHAR_CODES_COUNT && code == encoder_[c - 1]) {
      // Don't show the duplicate entry.
      continue;
    }
    encoding.add_str_int("", code(0));
    for (int i = 1; i < code.length(); ++i) {
      encoding.add_str_int(",", code(i));
    }
    encoding += "\t";
    if (c >= unicharset.size() || (0 < c && c < SPECIAL_UNICHAR_CODES_COUNT &&
                                   unicharset.has_special_codes())) {
      encoding += kNullChar;
    } else {
      encoding += unicharset.id_to_unichar(c);
    }
    encoding += "\n";
  }
  return encoding;
}

// Helper decomposes a Hangul unicode to 3 parts, leading, vowel, trailing.
// Note that the returned values are 0-based indices, NOT unicode Jamo.
// Returns false if the input is not in the Hangul unicode range.
/* static */
bool UnicharCompress::DecomposeHangul(int unicode, int* leading, int* vowel,
                                      int* trailing) {
  if (unicode < kFirstHangul) return false;
  int offset = unicode - kFirstHangul;
  if (offset >= kNumHangul) return false;
  const int kNCount = kVCount * kTCount;
  *leading = offset / kNCount;
  *vowel = (offset % kNCount) / kTCount;
  *trailing = offset % kTCount;
  return true;
}

// Computes the value of code_range_ from the encoder_.
void UnicharCompress::ComputeCodeRange() {
  code_range_ = -1;
  for (int c = 0; c < encoder_.size(); ++c) {
    const RecodedCharID& code = encoder_[c];
    for (int i = 0; i < code.length(); ++i) {
      if (code(i) > code_range_) code_range_ = code(i);
    }
  }
  ++code_range_;
}

// Initializes the decoding hash_map from the encoding array.
void UnicharCompress::SetupDecoder() {
  Cleanup();
  is_valid_start_.init_to_size(code_range_, false);
  for (int c = 0; c < encoder_.size(); ++c) {
    const RecodedCharID& code = encoder_[c];
    if (code.self_normalized() || decoder_.find(code) == decoder_.end())
      decoder_[code] = c;
    is_valid_start_[code(0)] = true;
    RecodedCharID prefix = code;
    int len = code.length() - 1;
    prefix.Truncate(len);
    auto final_it = final_codes_.find(prefix);
    if (final_it == final_codes_.end()) {
      GenericVectorEqEq<int>* code_list = new GenericVectorEqEq<int>;
      code_list->push_back(code(len));
      final_codes_[prefix] = code_list;
      while (--len >= 0) {
        prefix.Truncate(len);
        auto next_it = next_codes_.find(prefix);
        if (next_it == next_codes_.end()) {
          GenericVectorEqEq<int>* code_list = new GenericVectorEqEq<int>;
          code_list->push_back(code(len));
          next_codes_[prefix] = code_list;
        } else {
          // We still have to search the list as we may get here via multiple
          // lengths of code.
          if (!next_it->second->contains(code(len)))
            next_it->second->push_back(code(len));
          break;  // This prefix has been processed.
        }
      }
    } else {
      if (!final_it->second->contains(code(len)))
        final_it->second->push_back(code(len));
    }
  }
}

// Frees allocated memory.
void UnicharCompress::Cleanup() {
  decoder_.clear();
  is_valid_start_.clear();
  for (auto it = next_codes_.begin(); it != next_codes_.end(); ++it) {
    delete it->second;
  }
  for (auto it = final_codes_.begin(); it != final_codes_.end(); ++it) {
    delete it->second;
  }
  next_codes_.clear();
  final_codes_.clear();
}

}  // namespace tesseract.