freerdp/winpr/libwinpr/crt/utf.c

/*
 * Copyright 2001-2004 Unicode, Inc.
 *
 * Disclaimer
 *
 * This source code is provided as is by Unicode, Inc. No claims are
 * made as to fitness for any particular purpose. No warranties of any
 * kind are expressed or implied. The recipient agrees to determine
 * applicability of information provided. If this file has been
 * purchased on magnetic or optical media from Unicode, Inc., the
 * sole remedy for any claim will be exchange of defective media
 * within 90 days of receipt.
 *
 * Limitations on Rights to Redistribute This Code
 *
 * Unicode, Inc. hereby grants the right to freely use the information
 * supplied in this file in the creation of products supporting the
 * Unicode Standard, and to make copies of this file in any form
 * for internal or external distribution as long as this notice
 * remains attached.
 */

/* ---------------------------------------------------------------------

    Conversions between UTF32, UTF-16, and UTF-8. Source code file.
    Author: Mark E. Davis, 1994.
    Rev History: Rick McGowan, fixes & updates May 2001.
    Sept 2001: fixed const & error conditions per
    mods suggested by S. Parent & A. Lillich.
    June 2002: Tim Dodd added detection and handling of incomplete
    source sequences, enhanced error detection, added casts
    to eliminate compiler warnings.
    July 2003: slight mods to back out aggressive FFFE detection.
    Jan 2004: updated switches in from-UTF8 conversions.
    Oct 2004: updated to use UNI_MAX_LEGAL_UTF32 in UTF-32 conversions.

    See the header file "utf.h" for complete documentation.

------------------------------------------------------------------------ */

#include "utf.h"
#include <winpr/endian.h>

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wimplicit-fallthrough"
static const int halfShift = 10; /* used for shifting by 10 bits */

static const DWORD halfBase = 0x0010000UL;
static const DWORD halfMask = 0x3FFUL;

#define UNI_SUR_HIGH_START (DWORD)0xD800
#define UNI_SUR_HIGH_END (DWORD)0xDBFF
#define UNI_SUR_LOW_START (DWORD)0xDC00
#define UNI_SUR_LOW_END (DWORD)0xDFFF

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF32toUTF16(const DWORD** sourceStart, const DWORD* sourceEnd,
                                     WCHAR** targetStart, WCHAR* targetEnd, ConversionFlags flags)
{
	ConversionResult result = conversionOK;
	const DWORD* source = *sourceStart;
	WCHAR* target = *targetStart;

	while (source < sourceEnd)
	{
		DWORD ch;

		if (target >= targetEnd)
		{
			result = targetExhausted;
			break;
		}

		ch = *source++;

		if (ch <= UNI_MAX_BMP) /* Target is a character <= 0xFFFF */
		{
			/* UTF-16 surrogate values are illegal in UTF-32; 0xffff or 0xfffe are both reserved
			 * values */
			if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
			{
				if (flags == strictConversion)
				{
					--source; /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
				else
				{
					*target++ = UNI_REPLACEMENT_CHAR;
				}
			}
			else
			{
				*target++ = (WCHAR)ch; /* normal case */
			}
		}
		else if (ch > UNI_MAX_LEGAL_UTF32)
		{
			if (flags == strictConversion)
			{
				result = sourceIllegal;
			}
			else
			{
				*target++ = UNI_REPLACEMENT_CHAR;
			}
		}
		else
		{
			/* target is a character in range 0xFFFF - 0x10FFFF. */
			if (target + 1 >= targetEnd)
			{
				--source; /* Back up source pointer! */
				result = targetExhausted;
				break;
			}

			ch -= halfBase;
			*target++ = (WCHAR)((ch >> halfShift) + UNI_SUR_HIGH_START);
			*target++ = (WCHAR)((ch & halfMask) + UNI_SUR_LOW_START);
		}
	}

	*sourceStart = source;
	*targetStart = target;
	return result;
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF16toUTF32(const WCHAR** sourceStart, const WCHAR* sourceEnd,
                                     DWORD** targetStart, DWORD* targetEnd, ConversionFlags flags)
{
	ConversionResult result = conversionOK;
	const WCHAR* source = *sourceStart;
	DWORD* target = *targetStart;
	DWORD ch, ch2;

	while (source < sourceEnd)
	{
		const WCHAR* oldSource =
		    source; /*  In case we have to back up because of target overflow. */
		ch = *source++;

		/* If we have a surrogate pair, convert to UTF32 first. */
		if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END)
		{
			/* If the 16 bits following the high surrogate are in the source buffer... */
			if (source < sourceEnd)
			{
				ch2 = *source;

				/* If it's a low surrogate, convert to UTF32. */
				if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END)
				{
					ch = ((ch - UNI_SUR_HIGH_START) << halfShift) + (ch2 - UNI_SUR_LOW_START) +
					     halfBase;
					++source;
				}
				else if (flags == strictConversion) /* it's an unpaired high surrogate */
				{
					--source; /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
			}
			else /* We don't have the 16 bits following the high surrogate. */
			{
				--source; /* return to the high surrogate */
				result = sourceExhausted;
				break;
			}
		}
		else if (flags == strictConversion)
		{
			/* UTF-16 surrogate values are illegal in UTF-32 */
			if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END)
			{
				--source; /* return to the illegal value itself */
				result = sourceIllegal;
				break;
			}
		}

		if (target >= targetEnd)
		{
			source = oldSource; /* Back up source pointer! */
			result = targetExhausted;
			break;
		}

		*target++ = ch;
	}

	*sourceStart = source;
	*targetStart = target;
#ifdef CVTUTF_DEBUG

	if (result == sourceIllegal)
	{
		WLOG_WARN(TAG, "ConvertUTF16toUTF32 illegal seq 0x%04x,%04x", ch, ch2);
	}

#endif
	return result;
}

/* --------------------------------------------------------------------- */

/*
 * Index into the table below with the first byte of a UTF-8 sequence to
 * get the number of trailing bytes that are supposed to follow it.
 * Note that *legal* UTF-8 values can't have 4 or 5-bytes. The table is
 * left as-is for anyone who may want to do such conversion, which was
 * allowed in earlier algorithms.
 */
static const char trailingBytesForUTF8[256] = {
	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, 5, 5
};

/*
 * Magic values subtracted from a buffer value during UTF8 conversion.
 * This table contains as many values as there might be trailing bytes
 * in a UTF-8 sequence.
 */
static const DWORD offsetsFromUTF8[6] = { 0x00000000UL, 0x00003080UL, 0x000E2080UL,
	                                      0x03C82080UL, 0xFA082080UL, 0x82082080UL };

/*
 * Once the bits are split out into bytes of UTF-8, this is a mask OR-ed
 * into the first byte, depending on how many bytes follow.  There are
 * as many entries in this table as there are UTF-8 sequence types.
 * (I.e., one byte sequence, two byte... etc.). Remember that sequencs
 * for *legal* UTF-8 will be 4 or fewer bytes total.
 */
static const BYTE firstByteMark[7] = { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };

/* --------------------------------------------------------------------- */

/* The interface converts a whole buffer to avoid function-call overhead.
 * Constants have been gathered. Loops & conditionals have been removed as
 * much as possible for efficiency, in favor of drop-through switches.
 * (See "Note A" at the bottom of the file for equivalent code.)
 * If your compiler supports it, the "isLegalUTF8" call can be turned
 * into an inline function.
 */

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF16toUTF8(const WCHAR** sourceStart, const WCHAR* sourceEnd,
                                    BYTE** targetStart, BYTE* te, ConversionFlags flags)
{
	size_t pos = 0;
	size_t end = 0;
	const WCHAR* source;
	const BOOL computeLength = (!te) ? TRUE : FALSE;
	ConversionResult result = conversionOK;

	if (targetStart && te)
	{
		const size_t s = (size_t)*targetStart;
		const size_t e = (size_t)te;
		if (s > e)
			return sourceIllegal;
		end = e - s;
	}

	source = *sourceStart;

	while (source < sourceEnd)
	{
		DWORD ch;
		unsigned short bytesToWrite = 0;
		const DWORD byteMask = 0xBF;
		const DWORD byteMark = 0x80;
		const WCHAR* oldSource =
		    source; /* In case we have to back up because of target overflow. */
		Data_Read_UINT16(source, ch);
		source++;

		/* If we have a surrogate pair, convert to UTF32 first. */
		if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END)
		{
			/* If the 16 bits following the high surrogate are in the source buffer... */
			if (source < sourceEnd)
			{
				DWORD ch2;
				Data_Read_UINT16(source, ch2);

				/* If it's a low surrogate, convert to UTF32. */
				if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END)
				{
					ch = ((ch - UNI_SUR_HIGH_START) << halfShift) + (ch2 - UNI_SUR_LOW_START) +
					     halfBase;
					++source;
				}
				else if (flags == strictConversion)
				{
					/* it's an unpaired high surrogate */
					--source; /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
			}
			else
			{
				/* We don't have the 16 bits following the high surrogate. */
				--source; /* return to the high surrogate */
				result = sourceExhausted;
				break;
			}
		}
		else if (flags == strictConversion)
		{
			/* UTF-16 surrogate values are illegal in UTF-32 */
			if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END)
			{
				--source; /* return to the illegal value itself */
				result = sourceIllegal;
				break;
			}
		}

		/* Figure out how many bytes the result will require */
		if (ch < (DWORD)0x80)
		{
			bytesToWrite = 1;
		}
		else if (ch < (DWORD)0x800)
		{
			bytesToWrite = 2;
		}
		else if (ch < (DWORD)0x10000)
		{
			bytesToWrite = 3;
		}
		else if (ch < (DWORD)0x110000)
		{
			bytesToWrite = 4;
		}
		else
		{
			bytesToWrite = 3;
			ch = UNI_REPLACEMENT_CHAR;
		}

		pos += bytesToWrite;

		if ((pos > end) && (!computeLength))
		{
			source = oldSource; /* Back up source pointer! */
			pos -= bytesToWrite;
			result = targetExhausted;
			break;
		}

		if (!computeLength)
		{
			switch (bytesToWrite)
			{
				/* note: everything falls through. */
				case 4:
					(*targetStart)[--pos] = (BYTE)((ch | byteMark) & byteMask);
					ch >>= 6;

				case 3:
					(*targetStart)[--pos] = (BYTE)((ch | byteMark) & byteMask);
					ch >>= 6;

				case 2:
					(*targetStart)[--pos] = (BYTE)((ch | byteMark) & byteMask);
					ch >>= 6;

				case 1:
					(*targetStart)[--pos] = (BYTE)(ch | firstByteMark[bytesToWrite]);
			}
		}
		else
		{
			switch (bytesToWrite)
			{
				/* note: everything falls through. */
				case 4:
					--pos;

				case 3:
					--pos;

				case 2:
					--pos;

				case 1:
					--pos;
			}
		}

		pos += bytesToWrite;
	}

	*sourceStart = source;
	if (targetStart && *targetStart)
		*targetStart = &(*targetStart)[pos];
	else if (targetStart)
		*targetStart = (BYTE*)pos;
	return result;
}

/* --------------------------------------------------------------------- */

/*
 * Utility routine to tell whether a sequence of bytes is legal UTF-8.
 * This must be called with the length pre-determined by the first byte.
 * If not calling this from ConvertUTF8to*, then the length can be set by:
 *  length = trailingBytesForUTF8[*source]+1;
 * and the sequence is illegal right away if there aren't that many bytes
 * available.
 * If presented with a length > 4, this returns FALSE.  The Unicode
 * definition of UTF-8 goes up to 4-byte sequences.
 */

static BOOL isLegalUTF8(const BYTE* source, int length)
{
	BYTE a;
	const BYTE* srcptr = source + length;

	switch (length)
	{
		default:
			return FALSE;

		/* Everything else falls through when "TRUE"... */
		case 4:
			if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
				return FALSE;

		case 3:
			if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
				return FALSE;

		case 2:
			if ((a = (*--srcptr)) > 0xBF)
				return FALSE;

			switch (*source)
			{
				/* no fall-through in this inner switch */
				case 0xE0:
					if (a < 0xA0)
						return FALSE;

					break;

				case 0xED:
					if (a > 0x9F)
						return FALSE;

					break;

				case 0xF0:
					if (a < 0x90)
						return FALSE;

					break;

				case 0xF4:
					if (a > 0x8F)
						return FALSE;

					break;

				default:
					if (a < 0x80)
						return FALSE;
			}

		case 1:
			if (*source >= 0x80 && *source < 0xC2)
				return FALSE;
	}

	if (*source > 0xF4)
		return FALSE;

	return TRUE;
}

/* --------------------------------------------------------------------- */

/*
 * Exported function to return whether a UTF-8 sequence is legal or not.
 * This is not used here; it's just exported.
 */
BOOL isLegalUTF8Sequence(const BYTE* source, const BYTE* sourceEnd)
{
	int length = trailingBytesForUTF8[*source] + 1;

	if (source + length > sourceEnd)
		return FALSE;

	return isLegalUTF8(source, length);
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF8toUTF16(const BYTE** sourceStart, const BYTE* sourceEnd,
                                    WCHAR** targetStart, WCHAR* targetEnd, ConversionFlags flags)
{
	size_t target = 0;
	size_t end = 0;
	const BYTE* source;
	BOOL computeLength;
	ConversionResult result;
	computeLength = (!targetEnd) ? TRUE : FALSE;
	result = conversionOK;
	source = *sourceStart;

	if (targetStart && targetEnd)
	{
		const size_t s = (size_t)*targetStart;
		const size_t e = (size_t)targetEnd;
		if (s > e)
			return sourceIllegal;

		end = ((size_t)(targetEnd)) - ((size_t)(*targetStart));
	}

	while (source < sourceEnd)
	{
		DWORD ch = 0;
		unsigned short extraBytesToRead = trailingBytesForUTF8[*source];

		if ((source + extraBytesToRead) >= sourceEnd)
		{
			result = sourceExhausted;
			break;
		}

		/* Do this check whether lenient or strict */
		if (!isLegalUTF8(source, extraBytesToRead + 1))
		{
			result = sourceIllegal;
			break;
		}

		/*
		 * The cases all fall through. See "Note A" below.
		 */
		switch (extraBytesToRead)
		{
			case 5:
				ch += *source++;
				ch <<= 6; /* remember, illegal UTF-8 */

			case 4:
				ch += *source++;
				ch <<= 6; /* remember, illegal UTF-8 */

			case 3:
				ch += *source++;
				ch <<= 6;

			case 2:
				ch += *source++;
				ch <<= 6;

			case 1:
				ch += *source++;
				ch <<= 6;

			case 0:
				ch += *source++;
		}

		ch -= offsetsFromUTF8[extraBytesToRead];

		if ((target * sizeof(WCHAR) >= end) && (!computeLength))
		{
			source -= (extraBytesToRead + 1); /* Back up source pointer! */
			result = targetExhausted;
			break;
		}

		if (ch <= UNI_MAX_BMP)
		{
			/* Target is a character <= 0xFFFF */
			/* UTF-16 surrogate values are illegal in UTF-32 */
			if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
			{
				if (flags == strictConversion)
				{
					source -= (extraBytesToRead + 1); /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
				else
				{
					if (!computeLength)
						Data_Write_UINT16(&(*targetStart)[target], UNI_REPLACEMENT_CHAR);
					target++;
				}
			}
			else
			{
				if (!computeLength)
					Data_Write_UINT16(&(*targetStart)[target], ch); /* normal case */
				target++;
			}
		}
		else if (ch > UNI_MAX_UTF16)
		{
			if (flags == strictConversion)
			{
				result = sourceIllegal;
				source -= (extraBytesToRead + 1); /* return to the start */
				break;                            /* Bail out; shouldn't continue */
			}
			else
			{
				if (!computeLength)
					Data_Write_UINT16(&(*targetStart)[target], UNI_REPLACEMENT_CHAR);
				target++;
			}
		}
		else
		{
			/* target is a character in range 0xFFFF - 0x10FFFF. */
			if (((target + 1) * sizeof(WCHAR) >= end) && (!computeLength))
			{
				source -= (extraBytesToRead + 1); /* Back up source pointer! */
				result = targetExhausted;
				break;
			}

			ch -= halfBase;

			if (!computeLength)
			{
				WCHAR wchar;
				wchar = (ch >> halfShift) + UNI_SUR_HIGH_START;
				Data_Write_UINT16(&(*targetStart)[target++], wchar);
				wchar = (ch & halfMask) + UNI_SUR_LOW_START;
				Data_Write_UINT16(&(*targetStart)[target++], wchar);
			}
			else
			{
				target++;
				target++;
			}
		}
	}

	*sourceStart = source;
	if (targetStart && (*targetStart))
		*targetStart = &(*targetStart)[target];
	else if (targetStart)
		*targetStart = (WCHAR*)(target * sizeof(WCHAR));
	return result;
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF32toUTF8(const DWORD** sourceStart, const DWORD* sourceEnd,
                                    BYTE** targetStart, BYTE* targetEnd, ConversionFlags flags)
{
	ConversionResult result = conversionOK;
	const DWORD* source = *sourceStart;
	BYTE* target = *targetStart;

	while (source < sourceEnd)
	{
		DWORD ch;
		unsigned short bytesToWrite = 0;
		const DWORD byteMask = 0xBF;
		const DWORD byteMark = 0x80;
		ch = *source++;

		if (flags == strictConversion)
		{
			/* UTF-16 surrogate values are illegal in UTF-32 */
			if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
			{
				--source; /* return to the illegal value itself */
				result = sourceIllegal;
				break;
			}
		}

		/*
		 * Figure out how many bytes the result will require. Turn any
		 * illegally large UTF32 things (> Plane 17) into replacement chars.
		 */
		if (ch < (DWORD)0x80)
		{
			bytesToWrite = 1;
		}
		else if (ch < (DWORD)0x800)
		{
			bytesToWrite = 2;
		}
		else if (ch < (DWORD)0x10000)
		{
			bytesToWrite = 3;
		}
		else if (ch <= UNI_MAX_LEGAL_UTF32)
		{
			bytesToWrite = 4;
		}
		else
		{
			bytesToWrite = 3;
			ch = UNI_REPLACEMENT_CHAR;
			result = sourceIllegal;
		}

		target += bytesToWrite;

		if (target > targetEnd)
		{
			--source; /* Back up source pointer! */
			target -= bytesToWrite;
			result = targetExhausted;
			break;
		}

		switch (bytesToWrite) /* note: everything falls through. */
		{
			case 4:
				*--target = (BYTE)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 3:
				*--target = (BYTE)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 2:
				*--target = (BYTE)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 1:
				*--target = (BYTE)(ch | firstByteMark[bytesToWrite]);
		}

		target += bytesToWrite;
	}

	*sourceStart = source;
	*targetStart = target;
	return result;
}

/* --------------------------------------------------------------------- */

ConversionResult ConvertUTF8toUTF32(const BYTE** sourceStart, const BYTE* sourceEnd,
                                    DWORD** targetStart, DWORD* targetEnd, ConversionFlags flags)
{
	ConversionResult result = conversionOK;
	const BYTE* source = *sourceStart;
	DWORD* target = *targetStart;

	while (source < sourceEnd)
	{
		DWORD ch = 0;
		unsigned short extraBytesToRead = trailingBytesForUTF8[*source];

		if (source + extraBytesToRead >= sourceEnd)
		{
			result = sourceExhausted;
			break;
		}

		/* Do this check whether lenient or strict */
		if (!isLegalUTF8(source, extraBytesToRead + 1))
		{
			result = sourceIllegal;
			break;
		}

		/*
		 * The cases all fall through. See "Note A" below.
		 */
		switch (extraBytesToRead)
		{
			case 5:
				ch += *source++;
				ch <<= 6;

			case 4:
				ch += *source++;
				ch <<= 6;

			case 3:
				ch += *source++;
				ch <<= 6;

			case 2:
				ch += *source++;
				ch <<= 6;

			case 1:
				ch += *source++;
				ch <<= 6;

			case 0:
				ch += *source++;
		}

		ch -= offsetsFromUTF8[extraBytesToRead];

		if (target >= targetEnd)
		{
			source -= (extraBytesToRead + 1); /* Back up the source pointer! */
			result = targetExhausted;
			break;
		}

		if (ch <= UNI_MAX_LEGAL_UTF32)
		{
			/*
			 * UTF-16 surrogate values are illegal in UTF-32, and anything
			 * over Plane 17 (> 0x10FFFF) is illegal.
			 */
			if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
			{
				if (flags == strictConversion)
				{
					source -= (extraBytesToRead + 1); /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
				else
				{
					*target++ = UNI_REPLACEMENT_CHAR;
				}
			}
			else
			{
				*target++ = ch;
			}
		}
		else /* i.e., ch > UNI_MAX_LEGAL_UTF32 */
		{
			result = sourceIllegal;
			*target++ = UNI_REPLACEMENT_CHAR;
		}
	}

	*sourceStart = source;
	*targetStart = target;
	return result;
}

/* ---------------------------------------------------------------------

    Note A.
    The fall-through switches in UTF-8 reading code save a
    temp variable, some decrements & conditionals.  The switches
    are equivalent to the following loop:
    {
        int tmpBytesToRead = extraBytesToRead+1;
        do {
        ch += *source++;
        --tmpBytesToRead;
        if (tmpBytesToRead) ch <<= 6;
        } while (tmpBytesToRead > 0);
    }
    In UTF-8 writing code, the switches on "bytesToWrite" are
    similarly unrolled loops.

   --------------------------------------------------------------------- */
#pragma GCC diagnostic pop