Program Listing for File unicode_conversions.h¶
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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT license.
// This was extracted from https://github.com/microsoft/cpprestsdk/blob/cdae258bfb22f948c7b768b4dc56f5f4a2d9b2ce/Release/src/utilities/asyncrt_utils.cpp#L305
#include <string>
#include <stdexcept>
typedef std::basic_string<uint16_t> utf16string;
#define LOW_3BITS 0x7
#define LOW_4BITS 0xF
#define LOW_5BITS 0x1F
#define LOW_6BITS 0x3F
#define BIT4 0x8
#define BIT5 0x10
#define BIT6 0x20
#define BIT7 0x40
#define BIT8 0x80
#define L_SURROGATE_START 0xDC00
#define L_SURROGATE_END 0xDFFF
#define H_SURROGATE_START 0xD800
#define H_SURROGATE_END 0xDBFF
#define SURROGATE_PAIR_START 0x10000
// Create a dedicated type for characters to avoid the issue
// of different platforms defaulting char to be either signed
// or unsigned.
using UtilCharInternal_t = signed char;
inline size_t count_utf8_to_utf16(const std::string& s)
{
const size_t sSize = s.size();
auto const sData = reinterpret_cast<const UtilCharInternal_t*>(s.data());
size_t result {sSize};
for (size_t index = 0; index < sSize;)
{
if (sData[index] >= 0)
{
// use fast inner loop to skip single byte code points (which are
// expected to be the most frequent)
while ((++index < sSize) && (sData[index] >= 0))
;
if (index >= sSize) break;
}
// start special handling for multi-byte code points
const UtilCharInternal_t c {sData[index++]};
if ((c & BIT7) == 0)
{
throw std::range_error("UTF-8 string character can never start with 10xxxxxx");
}
else if ((c & BIT6) == 0) // 2 byte character, 0x80 to 0x7FF
{
if (index == sSize)
{
throw std::range_error("UTF-8 string is missing bytes in character");
}
const UtilCharInternal_t c2 {sData[index++]};
if ((c2 & 0xC0) != BIT8)
{
throw std::range_error("UTF-8 continuation byte is missing leading bit mask");
}
// can't require surrogates for 7FF
--result;
}
else if ((c & BIT5) == 0) // 3 byte character, 0x800 to 0xFFFF
{
if (sSize - index < 2)
{
throw std::range_error("UTF-8 string is missing bytes in character");
}
const UtilCharInternal_t c2 {sData[index++]};
const UtilCharInternal_t c3 {sData[index++]};
if (((c2 | c3) & 0xC0) != BIT8)
{
throw std::range_error("UTF-8 continuation byte is missing leading bit mask");
}
result -= 2;
}
else if ((c & BIT4) == 0) // 4 byte character, 0x10000 to 0x10FFFF
{
if (sSize - index < 3)
{
throw std::range_error("UTF-8 string is missing bytes in character");
}
const UtilCharInternal_t c2 {sData[index++]};
const UtilCharInternal_t c3 {sData[index++]};
const UtilCharInternal_t c4 {sData[index++]};
if (((c2 | c3 | c4) & 0xC0) != BIT8)
{
throw std::range_error("UTF-8 continuation byte is missing leading bit mask");
}
const uint32_t codePoint =
((c & LOW_3BITS) << 18) | ((c2 & LOW_6BITS) << 12) | ((c3 & LOW_6BITS) << 6) | (c4 & LOW_6BITS);
result -= (3 - (codePoint >= SURROGATE_PAIR_START));
}
else
{
throw std::range_error("UTF-8 string has invalid Unicode code point");
}
}
return result;
}
utf16string /*__cdecl conversions::*/utf8_to_utf16(const std::string& s)
{
// Save repeated heap allocations, use the length of resulting sequence.
const size_t srcSize = s.size();
auto const srcData = reinterpret_cast<const UtilCharInternal_t*>(s.data());
utf16string dest(count_utf8_to_utf16(s), L'\0');
utf16string::value_type* const destData = &dest[0];
size_t destIndex = 0;
for (size_t index = 0; index < srcSize; ++index)
{
UtilCharInternal_t src = srcData[index];
switch (src & 0xF0)
{
case 0xF0: // 4 byte character, 0x10000 to 0x10FFFF
{
const UtilCharInternal_t c2 {srcData[++index]};
const UtilCharInternal_t c3 {srcData[++index]};
const UtilCharInternal_t c4 {srcData[++index]};
uint32_t codePoint =
((src & LOW_3BITS) << 18) | ((c2 & LOW_6BITS) << 12) | ((c3 & LOW_6BITS) << 6) | (c4 & LOW_6BITS);
if (codePoint >= SURROGATE_PAIR_START)
{
// In UTF-16 U+10000 to U+10FFFF are represented as two 16-bit code units, surrogate pairs.
// - 0x10000 is subtracted from the code point
// - high surrogate is 0xD800 added to the top ten bits
// - low surrogate is 0xDC00 added to the low ten bits
codePoint -= SURROGATE_PAIR_START;
destData[destIndex++] = static_cast<utf16string::value_type>((codePoint >> 10) | H_SURROGATE_START);
destData[destIndex++] =
static_cast<utf16string::value_type>((codePoint & 0x3FF) | L_SURROGATE_START);
}
else
{
// In UTF-16 U+0000 to U+D7FF and U+E000 to U+FFFF are represented exactly as the Unicode code point
// value. U+D800 to U+DFFF are not valid characters, for simplicity we assume they are not present
// but will encode them if encountered.
destData[destIndex++] = static_cast<utf16string::value_type>(codePoint);
}
}
break;
case 0xE0: // 3 byte character, 0x800 to 0xFFFF
{
const UtilCharInternal_t c2 {srcData[++index]};
const UtilCharInternal_t c3 {srcData[++index]};
destData[destIndex++] = static_cast<utf16string::value_type>(
((src & LOW_4BITS) << 12) | ((c2 & LOW_6BITS) << 6) | (c3 & LOW_6BITS));
}
break;
case 0xD0: // 2 byte character, 0x80 to 0x7FF
case 0xC0:
{
const UtilCharInternal_t c2 {srcData[++index]};
destData[destIndex++] =
static_cast<utf16string::value_type>(((src & LOW_5BITS) << 6) | (c2 & LOW_6BITS));
}
break;
default: // single byte character, 0x0 to 0x7F
// try to use a fast inner loop for following single byte characters,
// since they are quite probable
do
{
destData[destIndex++] = static_cast<utf16string::value_type>(srcData[index++]);
} while (index < srcSize && srcData[index] > 0);
// adjust index since it will be incremented by the for loop
--index;
}
}
return dest;
}
inline size_t count_utf16_to_utf8(const utf16string& w)
{
const utf16string::value_type* const srcData = &w[0];
const size_t srcSize = w.size();
size_t destSize(srcSize);
for (size_t index = 0; index < srcSize; ++index)
{
const utf16string::value_type ch(srcData[index]);
if (ch <= 0x7FF)
{
if (ch > 0x7F) // 2 bytes needed (11 bits used)
{
++destSize;
}
}
// Check for high surrogate.
else if (ch >= H_SURROGATE_START && ch <= H_SURROGATE_END) // 4 bytes needed (21 bits used)
{
++index;
if (index == srcSize)
{
throw std::range_error("UTF-16 string is missing low surrogate");
}
const auto lowSurrogate = srcData[index];
if (lowSurrogate < L_SURROGATE_START || lowSurrogate > L_SURROGATE_END)
{
throw std::range_error("UTF-16 string has invalid low surrogate");
}
destSize += 2;
}
else // 3 bytes needed (16 bits used)
{
destSize += 2;
}
}
return destSize;
}
std::string /*__cdecl conversions::*/utf16_to_utf8(const utf16string& w)
{
const size_t srcSize = w.size();
const utf16string::value_type* const srcData = &w[0];
std::string dest(count_utf16_to_utf8(w), '\0');
std::string::value_type* const destData = &dest[0];
size_t destIndex(0);
for (size_t index = 0; index < srcSize; ++index)
{
const utf16string::value_type src = srcData[index];
if (src <= 0x7FF)
{
if (src <= 0x7F) // single byte character
{
destData[destIndex++] = static_cast<char>(src);
}
else // 2 bytes needed (11 bits used)
{
destData[destIndex++] = static_cast<char>(char((src >> 6) | 0xC0)); // leading 5 bits
destData[destIndex++] = static_cast<char>(char((src & LOW_6BITS) | BIT8)); // trailing 6 bits
}
}
// Check for high surrogate.
else if (src >= H_SURROGATE_START && src <= H_SURROGATE_END)
{
const auto highSurrogate = src;
const auto lowSurrogate = srcData[++index];
// To get from surrogate pair to Unicode code point:
// - subtract 0xD800 from high surrogate, this forms top ten bits
// - subtract 0xDC00 from low surrogate, this forms low ten bits
// - add 0x10000
// Leaves a code point in U+10000 to U+10FFFF range.
uint32_t codePoint = highSurrogate - H_SURROGATE_START;
codePoint <<= 10;
codePoint |= lowSurrogate - L_SURROGATE_START;
codePoint += SURROGATE_PAIR_START;
// 4 bytes needed (21 bits used)
destData[destIndex++] = static_cast<char>((codePoint >> 18) | 0xF0); // leading 3 bits
destData[destIndex++] = static_cast<char>(((codePoint >> 12) & LOW_6BITS) | BIT8); // next 6 bits
destData[destIndex++] = static_cast<char>(((codePoint >> 6) & LOW_6BITS) | BIT8); // next 6 bits
destData[destIndex++] = static_cast<char>((codePoint & LOW_6BITS) | BIT8); // trailing 6 bits
}
else // 3 bytes needed (16 bits used)
{
destData[destIndex++] = static_cast<char>((src >> 12) | 0xE0); // leading 4 bits
destData[destIndex++] = static_cast<char>(((src >> 6) & LOW_6BITS) | BIT8); // middle 6 bits
destData[destIndex++] = static_cast<char>((src & LOW_6BITS) | BIT8); // trailing 6 bits
}
}
return dest;
}