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49 lines
1.9 KiB
49 lines
1.9 KiB
/* |
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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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#ifndef LIBTEXTCLASSIFIER_UTIL_STRINGS_UTF8_H_ |
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#define LIBTEXTCLASSIFIER_UTIL_STRINGS_UTF8_H_ |
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namespace libtextclassifier { |
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// Returns the length (number of bytes) of the Unicode code point starting at |
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// src, based on inspecting just that one byte. Preconditions: src != NULL, |
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// *src can be read, and *src is not '\0', and src points to a well-formed UTF-8 |
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// std::string. |
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static inline int GetNumBytesForNonZeroUTF8Char(const char *src) { |
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// On most platforms, char is unsigned by default, but iOS is an exception. |
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// The cast below makes sure we always interpret *src as an unsigned char. |
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return "\1\1\1\1\1\1\1\1\1\1\1\1\2\2\3\4" |
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[(*(reinterpret_cast<const unsigned char *>(src)) & 0xFF) >> 4]; |
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} |
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// Like GetNumBytesForNonZeroUTF8Char, but *src may be '\0'; returns 0 in that |
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// case. |
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static inline int GetNumBytesForUTF8Char(const char *src) { |
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if (*src == '\0') return 0; |
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return GetNumBytesForNonZeroUTF8Char(src); |
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} |
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// Returns true if this byte is a trailing UTF-8 byte (10xx xxxx) |
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static inline bool IsTrailByte(char x) { |
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// return (x & 0xC0) == 0x80; |
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// Since trail bytes are always in [0x80, 0xBF], we can optimize: |
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return static_cast<signed char>(x) < -0x40; |
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} |
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} // namespace libtextclassifier |
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#endif // LIBTEXTCLASSIFIER_UTIL_STRINGS_UTF8_H_
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