/***********************************************************************
 * fs_unicode_utf.c
 *
 * Unicode UTF conversion functions
 * Copyright (C) 2007 QUALCOMM Technologies, Inc.
 *
 * This code converts strings between UTF8 and other encoding formats.
 *
 * This file was originally copied from Unicode.org:
 * http://www.unicode.org/Public/PROGRAMS/CVTUTF/
 *
 ***********************************************************************/

/*===========================================================================

                        EDIT HISTORY FOR MODULE

  This section contains comments describing changes made to the module.
  Notice that changes are listed in reverse chronological order.


when         who   what, where, why
----------   ---   ---------------------------------------------------------
2007-03-20   sh    Prefix all function calls to avoid collisions.
2007-03-11   sh    Simpler copyright.
2007-02-07   sh    Cleanup, removed unused code
2007-01-25   sh    Created from Unicode.org source file (ConvertUTF.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 "ConvertUTF.h" for complete documentation.

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


#include "fs_convert_utf.h"

static const int halfShift = 10;        /* used for shifting by 10 bits */

static const UTF32 halfBase = 0x0010000UL;
static const UTF32 halfMask = 0x3FFUL;

#define UNI_SUR_HIGH_START  (UTF32)0xD800
#define UNI_SUR_HIGH_END    (UTF32)0xDBFF
#define UNI_SUR_LOW_START   (UTF32)0xDC00
#define UNI_SUR_LOW_END     (UTF32)0xDFFF

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

ConversionResult
fs_ConvertUTF32toUTF16 (const UTF32 ** sourceStart, const UTF32 * sourceEnd,
                        UTF16 ** targetStart, UTF16 * targetEnd,
                        ConversionFlags flags)
{
  ConversionResult result = conversionOK;
  const UTF32 *source = *sourceStart;
  UTF16 *target = *targetStart;
  while (source < sourceEnd)
  {
    UTF32 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++ = (UTF16) 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++ = (UTF16) ((ch >> halfShift) + UNI_SUR_HIGH_START);
      *target++ = (UTF16) ((ch & halfMask) + UNI_SUR_LOW_START);
    }
  }
  *sourceStart = source;
  *targetStart = target;
  return result;
}

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

ConversionResult
fs_ConvertUTF16toUTF32 (const UTF16 ** sourceStart, const UTF16 * sourceEnd,
                        UTF32 ** targetStart, UTF32 * targetEnd,
                        ConversionFlags flags)
{
  ConversionResult result = conversionOK;
  const UTF16 *source = *sourceStart;
  UTF32 *target = *targetStart;
  UTF32 ch, ch2;
  while (source < sourceEnd)
  {
    /* In case we have to back up because of target overflow. */
    const UTF16 *oldSource = 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)
      {
        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;
  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 UTF32 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 UTF8 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 "fs_isLegalUTF8" call can be turned
 * into an inline function.
 */

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

ConversionResult
fs_ConvertUTF16toUTF8 (const UTF16 ** sourceStart, const UTF16 * sourceEnd,
                       UTF8 ** targetStart, UTF8 * targetEnd,
                       ConversionFlags flags)
{
  ConversionResult result = conversionOK;
  const UTF16 *source = *sourceStart;
  UTF8 *target = *targetStart;
  while (source < sourceEnd)
  {
    UTF32 ch;
    unsigned short bytesToWrite = 0;
    const UTF32 byteMask = 0xBF;
    const UTF32 byteMark = 0x80;
    /* In case we have to back up because of target overflow. */
    const UTF16 *oldSource = 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)
      {
        UTF32 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 < (UTF32) 0x80)
    {
      bytesToWrite = 1;
    }
    else if (ch < (UTF32) 0x800)
    {
      bytesToWrite = 2;
    }
    else if (ch < (UTF32) 0x10000)
    {
      bytesToWrite = 3;
    }
    else if (ch < (UTF32) 0x110000)
    {
      bytesToWrite = 4;
    }
    else
    {
      bytesToWrite = 3;
      ch = UNI_REPLACEMENT_CHAR;
    }

    target += bytesToWrite;
    if (target > targetEnd)
    {
      source = oldSource;       /* Back up source pointer! */
      target -= bytesToWrite;
      result = targetExhausted;
      break;
    }
    switch (bytesToWrite)
    {                           /* note: everything falls through. */
      case 4:
        *--target = (UTF8) ((ch | byteMark) & byteMask);
        ch >>= 6;
        //lint -fallthrough
      case 3:
        *--target = (UTF8) ((ch | byteMark) & byteMask);
        ch >>= 6;
        //lint -fallthrough
      case 2:
        *--target = (UTF8) ((ch | byteMark) & byteMask);
        ch >>= 6;
        //lint -fallthrough
      case 1:
        *--target = (UTF8) (ch | firstByteMark[bytesToWrite]);
    }
    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 0.  The Unicode
 * definition of UTF-8 goes up to 4-byte sequences.
 */

Boolean
fs_isLegalUTF8 (const UTF8 * source, int length)
{
  UTF8 a;
  const UTF8 *srcptr = source + length;
  switch (length)
  {
    default:
      return 0;
      /* Everything else falls through when "true"... */
    case 4:
      if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
        return 0;
      //lint -fallthrough
    case 3:
      if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
        return 0;
      //lint -fallthrough
    case 2:
      if ((a = (*--srcptr)) > 0xBF)
        return 0;

      switch (*source)
      {
        /* no fall-through in this inner switch */
        case 0xE0:
          if (a < 0xA0)
            return 0;
          break;
        case 0xED:
          if (a > 0x9F)
            return 0;
          break;
        case 0xF0:
          if (a < 0x90)
            return 0;
          break;
        case 0xF4:
          if (a > 0x8F)
            return 0;
          break;
        default:
          if (a < 0x80)
            return 0;
      }
      //lint -fallthrough
    case 1:
      if (*source >= 0x80 && *source < 0xC2)
        return 0;
  }
  if (*source > 0xF4)
    return 0;
  return 1;
}

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

ConversionResult
fs_ConvertUTF8toUTF16 (const UTF8 ** sourceStart, const UTF8 * sourceEnd,
                       UTF16 ** targetStart, UTF16 * targetEnd,
                       ConversionFlags flags)
{
  ConversionResult result = conversionOK;
  const UTF8 *source = *sourceStart;
  UTF16 *target = *targetStart;
  while (source < sourceEnd)
  {
    UTF32 ch = 0;
    unsigned short extraBytesToRead = trailingBytesForUTF8[*source];
    if (source + extraBytesToRead >= sourceEnd)
    {
      result = sourceExhausted;
      break;
    }
    /* Do this check whether lenient or strict */
    if (!fs_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 */
      //lint -fallthrough
      case 4:
        ch += *source++;
        ch <<= 6;               /* remember, illegal UTF-8 */
      //lint -fallthrough
      case 3:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      case 2:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      case 1:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      case 0:
        ch += *source++;
    }
    ch -= offsetsFromUTF8[extraBytesToRead];

    if (target >= targetEnd)
    {
      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)
        {
          /* return to the illegal value */
          source -= (extraBytesToRead + 1);
          result = sourceIllegal;
          break;
        }
        else
        {
          *target++ = UNI_REPLACEMENT_CHAR;
        }
      }
      else
      {
        *target++ = (UTF16) ch; /* normal case */
      }
    }
    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
      {
        *target++ = UNI_REPLACEMENT_CHAR;
      }
    }
    else
    {
      /* target is a character in range 0xFFFF - 0x10FFFF. */
      if (target + 1 >= targetEnd)
      {
        source -= (extraBytesToRead + 1);       /* Back up source pointer! */
        result = targetExhausted;
        break;
      }
      ch -= halfBase;
      *target++ = (UTF16) ((ch >> halfShift) + UNI_SUR_HIGH_START);
      *target++ = (UTF16) ((ch & halfMask) + UNI_SUR_LOW_START);
    }
  }
  *sourceStart = source;
  *targetStart = target;
  return result;
}

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

ConversionResult
fs_ConvertUTF32toUTF8 (const UTF32 ** sourceStart, const UTF32 * sourceEnd,
                       UTF8 ** targetStart, UTF8 * targetEnd,
                       ConversionFlags flags)
{
  ConversionResult result = conversionOK;
  const UTF32 *source = *sourceStart;
  UTF8 *target = *targetStart;
  while (source < sourceEnd)
  {
    UTF32 ch;
    unsigned short bytesToWrite = 0;
    const UTF32 byteMask = 0xBF;
    const UTF32 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 < (UTF32) 0x80)
    {
      bytesToWrite = 1;
    }
    else if (ch < (UTF32) 0x800)
    {
      bytesToWrite = 2;
    }
    else if (ch < (UTF32) 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 = (UTF8) ((ch | byteMark) & byteMask);
        ch >>= 6;
      //lint -fallthrough
      case 3:
        *--target = (UTF8) ((ch | byteMark) & byteMask);
        ch >>= 6;
      //lint -fallthrough
      case 2:
        *--target = (UTF8) ((ch | byteMark) & byteMask);
        ch >>= 6;
      //lint -fallthrough
      case 1:
        *--target = (UTF8) (ch | firstByteMark[bytesToWrite]);
    }
    target += bytesToWrite;
  }
  *sourceStart = source;
  *targetStart = target;
  return result;
}

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

ConversionResult
fs_ConvertUTF8toUTF32 (const UTF8 ** sourceStart, const UTF8 * sourceEnd,
                       UTF32 ** targetStart, UTF32 * targetEnd,
                       ConversionFlags flags)
{
  ConversionResult result = conversionOK;
  const UTF8 *source = *sourceStart;
  UTF32 *target = *targetStart;
  while (source < sourceEnd)
  {
    UTF32 ch = 0;
    unsigned short extraBytesToRead = trailingBytesForUTF8[*source];
    if (source + extraBytesToRead >= sourceEnd)
    {
      result = sourceExhausted;
      break;
    }
    /* Do this check whether lenient or strict */
    if (!fs_isLegalUTF8 (source, extraBytesToRead + 1))
    {
      result = sourceIllegal;
      break;
    }
    /*
     * The cases all fall through. See "Note A" below.
     */
    switch (extraBytesToRead)
    {
      case 5:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      case 4:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      case 3:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      case 2:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      case 1:
        ch += *source++;
        ch <<= 6;
      //lint -fallthrough
      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)
        {
          /* return to the illegal value */
          source -= (extraBytesToRead + 1);
          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.

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