/*
 * 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"

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) {
    fprintf(stderr, "ConvertUTF16toUTF32 illegal seq 0x%04x,%04x\n", ch, ch2);
    fflush(stderr);
}
#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* targetEnd, ConversionFlags flags)
{
	BYTE* target;
	const WCHAR* source;
	BOOL computeLength;
	ConversionResult result;

	computeLength = (!targetEnd) ? TRUE : FALSE;

	source = *sourceStart;
	target = *targetStart;
	result = conversionOK;

	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. */

		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 = *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;
			}
		}

		/* 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;
		}

		target += bytesToWrite;

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

		if (!computeLength)
		{
			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]);
			}
		}
		else
		{
			switch (bytesToWrite)
			{
				/* note: everything falls through. */

				case 4:
					--target;
					ch >>= 6;

				case 3:
					--target;
					ch >>= 6;

				case 2:
					--target;
					ch >>= 6;

				case 1:
					--target;
			}
		}

		target += bytesToWrite;
	}

	*sourceStart = source;
	*targetStart = target;

	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)
{
	WCHAR* target;
	const BYTE* source;
	BOOL computeLength;
	ConversionResult result;

	computeLength = (!targetEnd) ? TRUE : FALSE;

	result = conversionOK;
	source = *sourceStart;
	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; /* 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 >= targetEnd) && (!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)
						*target++ = UNI_REPLACEMENT_CHAR;
					else
						target++;
				}
			}
			else
			{
				if (!computeLength)
					*target++ = (WCHAR) ch; /* normal case */
				else
					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)
					*target++ = UNI_REPLACEMENT_CHAR;
				else
					target++;
			}
		}
		else
		{
			/* target is a character in range 0xFFFF - 0x10FFFF. */

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

			ch -= halfBase;

			if (!computeLength)
			{
				*target++ = (WCHAR)((ch >> halfShift) + UNI_SUR_HIGH_START);
				*target++ = (WCHAR)((ch & halfMask) + UNI_SUR_LOW_START);
			}
			else
			{
				target++;
				target++;
			}
		}
	}

	*sourceStart = source;
	*targetStart = target;

	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.

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