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// See www.openfst.org for extensive documentation on this weighted
// finite-state transducer library.
//
// This library implements an unrestricted Thompson/Pike UTF-8 parser and
// serializer. UTF-8 is a restricted subset of this byte stream encoding. See
// http://en.wikipedia.org/wiki/UTF-8 for a good description of the encoding
// details.
#ifndef FST_ICU_H_
#define FST_ICU_H_
#include <sstream>
#include <vector>
#include <fst/log.h>
namespace fst {
// This function writes UTF-8 codepoints into a vector of Labels, truncating if
// necessary. It is possible to use this sensibly with as little as 16 bits of
// Label precision (i.e., when all characters are within the Basic Multilingual
// Plane). With 21 bits, one can encode all UTF-8 codepoints, including those
// from the various Astral Planes. Naturally, it is safe to use this with larger
// Labels (e.g., 64 bits).
template <class Label>
bool UTF8StringToLabels(const string &str, std::vector<Label> *labels) {
const auto *data = str.data();
const auto length = str.size();
for (size_t i = 0; i < length;) {
int c = data[i++] & 0xff;
if ((c & 0x80) == 0) {
labels->push_back(c);
} else {
if ((c & 0xc0) == 0x80) {
LOG(ERROR) << "UTF8StringToLabels: Continuation byte as lead byte";
return false;
}
int count =
(c >= 0xc0) + (c >= 0xe0) + (c >= 0xf0) + (c >= 0xf8) + (c >= 0xfc);
int32 code = c & ((1 << (6 - count)) - 1);
while (count != 0) {
if (i == length) {
LOG(ERROR) << "UTF8StringToLabels: Truncated UTF-8 byte sequence";
return false;
}
char cb = data[i++];
if ((cb & 0xc0) != 0x80) {
LOG(ERROR) << "UTF8StringToLabels: Missing/invalid continuation byte";
return false;
}
code = (code << 6) | (cb & 0x3f);
count--;
}
if (code < 0) {
// Should be unreachable.
LOG(ERROR) << "UTF8StringToLabels: Invalid character found: " << c;
return false;
}
labels->push_back(code);
}
}
return true;
}
template <class Label>
bool LabelsToUTF8String(const std::vector<Label> &labels, string *str) {
std::ostringstream ostr;
for (size_t i = 0; i < labels.size(); ++i) {
int32 code = labels[i];
if (code < 0) {
LOG(ERROR) << "LabelsToUTF8String: Invalid character found: " << code;
return false;
} else if (code < 0x80) {
ostr << static_cast<char>(code);
} else if (code < 0x800) {
ostr << static_cast<char>((code >> 6) | 0xc0);
ostr << static_cast<char>((code & 0x3f) | 0x80);
} else if (code < 0x10000) {
ostr << static_cast<char>((code >> 12) | 0xe0);
ostr << static_cast<char>(((code >> 6) & 0x3f) | 0x80);
ostr << static_cast<char>((code & 0x3f) | 0x80);
} else if (code < 0x200000) {
ostr << static_cast<char>((code >> 18) | 0xf0);
ostr << static_cast<char>(((code >> 12) & 0x3f) | 0x80);
ostr << static_cast<char>(((code >> 6) & 0x3f) | 0x80);
ostr << static_cast<char>((code & 0x3f) | 0x80);
} else if (code < 0x4000000) {
ostr << static_cast<char>((code >> 24) | 0xf8);
ostr << static_cast<char>(((code >> 18) & 0x3f) | 0x80);
ostr << static_cast<char>(((code >> 12) & 0x3f) | 0x80);
ostr << static_cast<char>(((code >> 6) & 0x3f) | 0x80);
ostr << static_cast<char>((code & 0x3f) | 0x80);
} else {
ostr << static_cast<char>((code >> 30) | 0xfc);
ostr << static_cast<char>(((code >> 24) & 0x3f) | 0x80);
ostr << static_cast<char>(((code >> 18) & 0x3f) | 0x80);
ostr << static_cast<char>(((code >> 12) & 0x3f) | 0x80);
ostr << static_cast<char>(((code >> 6) & 0x3f) | 0x80);
ostr << static_cast<char>((code & 0x3f) | 0x80);
}
}
*str = ostr.str();
return true;
}
} // namespace fst
#endif // FST_ICU_H_
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