109 lines
3 KiB
C++
109 lines
3 KiB
C++
/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "lang_id/custom-tokenizer.h"
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#include <ctype.h>
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#include <string>
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#include "util/strings/utf8.h"
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namespace libtextclassifier {
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namespace nlp_core {
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namespace lang_id {
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namespace {
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inline bool IsTokenSeparator(int num_bytes, const char *curr) {
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if (num_bytes != 1) {
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return false;
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}
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return !isalpha(*curr);
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}
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} // namespace
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const char *GetSafeEndOfString(const char *data, size_t size) {
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const char *const hard_end = data + size;
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const char *curr = data;
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while (curr < hard_end) {
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int num_bytes = GetNumBytesForUTF8Char(curr);
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if (num_bytes == 0) {
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break;
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}
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const char *new_curr = curr + num_bytes;
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if (new_curr > hard_end) {
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return curr;
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}
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curr = new_curr;
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}
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return curr;
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}
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void TokenizeTextForLangId(const std::string &text, LightSentence *sentence) {
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const char *const start = text.data();
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const char *curr = start;
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const char *end = GetSafeEndOfString(start, text.size());
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// Corner case: empty safe part of the text.
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if (curr >= end) {
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return;
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}
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// Number of bytes for UTF8 character starting at *curr. Note: the loop below
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// is guaranteed to terminate because in each iteration, we move curr by at
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// least num_bytes, and num_bytes is guaranteed to be > 0.
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int num_bytes = GetNumBytesForNonZeroUTF8Char(curr);
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while (curr < end) {
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// Jump over consecutive token separators.
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while (IsTokenSeparator(num_bytes, curr)) {
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curr += num_bytes;
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if (curr >= end) {
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return;
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}
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num_bytes = GetNumBytesForNonZeroUTF8Char(curr);
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}
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// If control reaches this point, we are at beginning of a non-empty token.
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std::string *word = sentence->add_word();
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// Add special token-start character.
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word->push_back('^');
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// Add UTF8 characters to word, until we hit the end of the safe text or a
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// token separator.
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while (true) {
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word->append(curr, num_bytes);
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curr += num_bytes;
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if (curr >= end) {
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break;
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}
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num_bytes = GetNumBytesForNonZeroUTF8Char(curr);
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if (IsTokenSeparator(num_bytes, curr)) {
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curr += num_bytes;
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num_bytes = GetNumBytesForNonZeroUTF8Char(curr);
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break;
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}
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}
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word->push_back('$');
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// Note: we intentionally do not token.set_start()/end(), as those fields
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// are not used by the langid model.
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}
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}
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} // namespace lang_id
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} // namespace nlp_core
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} // namespace libtextclassifier
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