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template <typename T>
void utf8_to_string(std::basic_string<T> &dst, const unsigned char *buffer, size_t n){
static const unsigned char utf8_lengths[] = {
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 0, 0,
0xFF, 0x1F, 0x0F, 0x07, 0x03, 0x01
};
static const unsigned char bom[] = { 0xEF, 0xBB, 0xBF };
static const unsigned char *masks = utf8_lengths + 0x100;
if (n >= 3 && !memcmp(buffer, bom, 3)){
buffer += 3;
n -= 3;
}
boost::shared_array<T> temp(new T[n]);
T *temp_pointer = temp.get();
size_t writer = 0;
for (size_t i = 0; i != n;){
unsigned char byte = buffer[i++];
unsigned char length = utf8_lengths[byte];
if (length > n - i)
break;
unsigned wc = byte & masks[length];
for (;length; length--){
wc <<= 6;
wc |= (T)(buffer[i++] & 0x3F);
}
temp_pointer[writer++] = wc;
}
dst.assign(temp_pointer, temp_pointer + writer);
}
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