ustring.cpp   [plain text]

// -*- c-basic-offset: 2 -*-
/*
 *  This file is part of the KDE libraries
 *  Copyright (C) 1999-2000 Harri Porten (porten@kde.org)
 *  Copyright (C) 2003 Apple Computer, Inc.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Library General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Library General Public License for more details.
 *
 *  You should have received a copy of the GNU Library General Public License
 *  along with this library; see the file COPYING.LIB.  If not, write to
 *  the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 *  Boston, MA 02111-1307, USA.
 *
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_STRINGS_H
#include <strings.h>
#endif

#include "ustring.h"
#include "operations.h"
#include "identifier.h"
#include <math.h>
#include "dtoa.h"

namespace KJS {

extern const double NaN;
extern const double Inf;

CString::CString(const char *c)
{
  length = strlen(c);
  data = new char[length+1];
  memcpy(data, c, length + 1);
}

CString::CString(const char *c, int len)
{
  length = len;
  data = new char[len+1];
  memcpy(data, c, len);
  data[len] = 0;
}

CString::CString(const CString &b)
{
  length = b.length;
  data = new char[length+1];
  memcpy(data, b.data, length + 1);
}

CString::~CString()
{
  delete [] data;
}

CString &CString::append(const CString &t)
{
  char *n;
  n = new char[length+t.length+1];
  if (length)
    memcpy(n, data, length);
  if (t.length)
    memcpy(n+length, t.data, t.length);
  length += t.length;
  n[length] = 0;

  delete [] data;
  data = n;

  return *this;
}

CString &CString::operator=(const char *c)
{
  if (data)
    delete [] data;
  length = strlen(c);
  data = new char[length+1];
  memcpy(data, c, length + 1);

  return *this;
}

CString &CString::operator=(const CString &str)
{
  if (this == &str)
    return *this;

  if (data)
    delete [] data;
  length = str.length;
  data = new char[length + 1];
  memcpy(data, str.data, length + 1);

  return *this;
}

bool KJS::operator==(const KJS::CString& c1, const KJS::CString& c2)
{
  int len = c1.size();
  return len == c2.size() && (len == 0 || memcmp(c1.c_str(), c2.c_str(), len) == 0);
}

UString::Rep UString::Rep::null = { 0, 0, 0, 1, 1 };
UString::Rep UString::Rep::empty = { 0, 0, 0, 1, 1 };
const int normalStatBufferSize = 4096;
static char *statBuffer = 0;
static int statBufferSize = 0;

UChar UChar::toLower() const
{
  // ### properly support unicode tolower
  if (uc >= 256 || islower(uc))
    return *this;

  return (unsigned char)tolower(uc);
}

UChar UChar::toUpper() const
{
  if (uc >= 256 || isupper(uc))
    return *this;

  return (unsigned char)toupper(uc);
}

UCharReference& UCharReference::operator=(UChar c)
{
  str->detach();
  if (offset < str->rep->len)
    *(str->rep->dat + offset) = c;
  /* TODO: lengthen string ? */
  return *this;
}

UChar& UCharReference::ref() const
{
  if (offset < str->rep->len)
    return *(str->rep->dat + offset);
  else {
    static UChar callerBetterNotModifyThis('\0');
    return callerBetterNotModifyThis;
  }
}

UString::Rep *UString::Rep::create(UChar *d, int l)
{
  Rep *r = new Rep;
  r->dat = d;
  r->len = l;
  r->capacity = l;
  r->rc = 1;
  r->_hash = 0;
  return r;
}

void UString::Rep::destroy()
{
  if (capacity == capacityForIdentifier)
    Identifier::remove(this);
  delete [] dat;
  delete this;
}

// Golden ratio - arbitrary start value to avoid mapping all 0's to all 0's
// or anything like that.
const unsigned PHI = 0x9e3779b9U;

// This hash algorithm comes from:
// http://burtleburtle.net/bob/hash/hashfaq.html
// http://burtleburtle.net/bob/hash/doobs.html
unsigned UString::Rep::computeHash(const UChar *s, int length)
{
    int prefixLength = length < 8 ? length : 8;
    int suffixPosition = length < 16 ? 8 : length - 8;

    unsigned h = PHI;
    h += length;
    h += (h << 10); 
    h ^= (h << 6); 

    for (int i = 0; i < prefixLength; i++) {
        h += s[i].uc; 
	h += (h << 10); 
	h ^= (h << 6); 
    }
    for (int i = suffixPosition; i < length; i++){
        h += s[i].uc; 
	h += (h << 10); 
	h ^= (h << 6); 
    }

    h += (h << 3);
    h ^= (h >> 11);
    h += (h << 15);
 
    if (h == 0)
        h = 0x80000000;

    return h;
}

// This hash algorithm comes from:
// http://burtleburtle.net/bob/hash/hashfaq.html
// http://burtleburtle.net/bob/hash/doobs.html
unsigned UString::Rep::computeHash(const char *s)
{
    int length = strlen(s);
    int prefixLength = length < 8 ? length : 8;
    int suffixPosition = length < 16 ? 8 : length - 8;

    unsigned h = PHI;
    h += length;
    h += (h << 10); 
    h ^= (h << 6); 

    for (int i = 0; i < prefixLength; i++) {
        h += (unsigned char)s[i];
	h += (h << 10); 
	h ^= (h << 6); 
    }
    for (int i = suffixPosition; i < length; i++) {
        h += (unsigned char)s[i];
	h += (h << 10); 
	h ^= (h << 6); 
    }

    h += (h << 3);
    h ^= (h >> 11);
    h += (h << 15);

    if (h == 0)
        h = 0x80000000;

    return h;
}

UString::UString()
{
  attach(&Rep::null);
}

UString::UString(char c)
{
    UChar *d = new UChar[1];
    d[0] = c;
    rep = Rep::create(d, 1);
}

UString::UString(const char *c)
{
  if (!c) {
    attach(&Rep::null);
    return;
  }
  int length = strlen(c);
  if (length == 0) {
    attach(&Rep::empty);
    return;
  }
  UChar *d = new UChar[length];
  for (int i = 0; i < length; i++)
    d[i].uc = c[i];
  rep = Rep::create(d, length);
}

UString::UString(const UChar *c, int length)
{
  if (length == 0) {
    attach(&Rep::empty);
    return;
  }
  UChar *d = new UChar[length];
  memcpy(d, c, length * sizeof(UChar));
  rep = Rep::create(d, length);
}

UString::UString(UChar *c, int length, bool copy)
{
  if (length == 0) {
    attach(&Rep::empty);
    return;
  }
  UChar *d;
  if (copy) {
    d = new UChar[length];
    memcpy(d, c, length * sizeof(UChar));
  } else
    d = c;
  rep = Rep::create(d, length);
}

UString::UString(const UString &a, const UString &b)
{
  int aSize = a.size();
  int bSize = b.size();
  int length = aSize + bSize;
  if (length == 0) {
    attach(&Rep::empty);
    return;
  }
  UChar *d = new UChar[length];
  memcpy(d, a.data(), aSize * sizeof(UChar));
  memcpy(d + aSize, b.data(), bSize * sizeof(UChar));
  rep = Rep::create(d, length);
}

const UString &UString::null()
{
    static UString n;
    return n;
}

UString UString::from(int i)
{
  return from((long)i);
}

UString UString::from(unsigned int u)
{
  UChar buf[20];
  UChar *end = buf + 20;
  UChar *p = end;
  
  if (u == 0) {
    *--p = '0';
  } else {
    while (u) {
      *--p = (unsigned short)((u % 10) + '0');
      u /= 10;
    }
  }
  
  return UString(p, end - p);
}

UString UString::from(long l)
{
  UChar buf[20];
  UChar *end = buf + 20;
  UChar *p = end;
  
  if (l == 0) {
    *--p = '0';
  } else if (l == LONG_MIN) {
    char minBuf[20];
    sprintf(minBuf, "%ld", LONG_MIN);
    return UString(minBuf);
  } else {
    bool negative = false;
    if (l < 0) {
      negative = true;
      l = -l;
    }
    while (l) {
      *--p = (unsigned short)((l % 10) + '0');
      l /= 10;
    }
    if (negative) {
      *--p = '-';
    }
  }
  
  return UString(p, end - p);
}

UString UString::from(double d)
{
  char buf[80];
  int decimalPoint;
  int sign;
  
  char *result = kjs_dtoa(d, 0, 0, &decimalPoint, &sign, NULL);
  int length = strlen(result);
  
  int i = 0;
  if (sign) {
    buf[i++] = '-';
  }
  
  if (decimalPoint <= 0 && decimalPoint > -6) {
    buf[i++] = '0';
    buf[i++] = '.';
    for (int j = decimalPoint; j < 0; j++) {
      buf[i++] = '0';
    }
    strcpy(buf + i, result);
  } else if (decimalPoint <= 21 && decimalPoint > 0) {
    if (length <= decimalPoint) {
      strcpy(buf + i, result);
      i += length;
      for (int j = 0; j < decimalPoint - length; j++) {
	buf[i++] = '0';
      }
      buf[i] = '\0';
    } else {
      strncpy(buf + i, result, decimalPoint);
      i += decimalPoint;
      buf[i++] = '.';
      strcpy(buf + i, result + decimalPoint);
    }
  } else if (result[0] < '0' || result[0] > '9') {
    strcpy(buf + i, result);
  } else {
    buf[i++] = result[0];
    if (length > 1) {
      buf[i++] = '.';
      strcpy(buf + i, result + 1);
      i += length - 1;
    }
    
    buf[i++] = 'e';
    buf[i++] = (decimalPoint >= 0) ? '+' : '-';
    // decimalPoint can't be more than 3 digits decimal given the
    // nature of float representation
    int exponential = decimalPoint - 1;
    if (exponential < 0) {
      exponential = exponential * -1;
    }
    if (exponential >= 100) {
      buf[i++] = '0' + exponential / 100;
    }
    if (exponential >= 10) {
      buf[i++] = '0' + (exponential % 100) / 10;
    }
    buf[i++] = '0' + exponential % 10;
    buf[i++] = '\0';
  }
  
  kjs_freedtoa(result);
  
  return UString(buf);
}

UString &UString::append(const UString &t)
{
  int l = size();
  int tLen = t.size();
  int newLen = l + tLen;
  if (rep->rc == 1 && newLen <= rep->capacity) {
    memcpy(rep->dat+l, t.data(), tLen * sizeof(UChar));
    rep->len = newLen;
    rep->_hash = 0;
    return *this;
  }
  
  int newCapacity = (newLen * 3 + 1) / 2;
  UChar *n = new UChar[newCapacity];
  memcpy(n, data(), l * sizeof(UChar));
  memcpy(n+l, t.data(), tLen * sizeof(UChar));
  release();
  rep = Rep::create(n, newLen);
  rep->capacity = newCapacity;

  return *this;
}

UString &UString::append(const char *t)
{
  int l = size();
  int tLen = strlen(t);
  int newLen = l + tLen;
  if (rep->rc == 1 && newLen <= rep->capacity) {
    for (int i = 0; i < tLen; ++i)
      rep->dat[l+i] = t[i];
    rep->len = newLen;
    rep->_hash = 0;
    return *this;
  }
  
  int newCapacity = (newLen * 3 + 1) / 2;
  UChar *n = new UChar[newCapacity];
  memcpy(n, data(), l * sizeof(UChar));
  for (int i = 0; i < tLen; ++i)
    n[l+i] = t[i];
  release();
  rep = Rep::create(n, newLen);
  rep->capacity = newCapacity;

  return *this;
}

UString &UString::append(unsigned short c)
{
  int l = size();
  int newLen = l + 1;
  if (rep->rc == 1 && newLen <= rep->capacity) {
    rep->dat[l] = c;
    rep->len = newLen;
    rep->_hash = 0;
    return *this;
  }
  
  int newCapacity = (newLen * 3 + 1) / 2;
  UChar *n = new UChar[newCapacity];
  memcpy(n, data(), l * sizeof(UChar));
  n[l] = c;
  release();
  rep = Rep::create(n, newLen);
  rep->capacity = newCapacity;

  return *this;
}

CString UString::cstring() const
{
  return ascii();
}

char *UString::ascii() const
{
  // Never make the buffer smaller than normalStatBufferSize.
  // Thus we almost never need to reallocate.
  int length = size();
  int neededSize = length + 1;
  if (neededSize < normalStatBufferSize) {
    neededSize = normalStatBufferSize;
  }
  if (neededSize != statBufferSize) {
    delete [] statBuffer;
    statBuffer = new char [neededSize];
    statBufferSize = neededSize;
  }
  
  const UChar *p = data();
  char *q = statBuffer;
  const UChar *limit = p + length;
  while (p != limit) {
    *q = p->uc;
    ++p;
    ++q;
  }
  *q = '\0';

  return statBuffer;
}

#ifdef KJS_DEBUG_MEM
void UString::globalClear()
{
  delete [] statBuffer;
  statBuffer = 0;
  statBufferSize = 0;
}
#endif

UString &UString::operator=(const char *c)
{
  int l = c ? strlen(c) : 0;
  UChar *d;
  if (rep->rc == 1 && l <= rep->capacity) {
    d = rep->dat;
    rep->_hash = 0;
  } else {
    release();
    d = new UChar[l];
    rep = Rep::create(d, l);
  }
  for (int i = 0; i < l; i++)
    d[i].uc = c[i];

  return *this;
}

UString &UString::operator=(const UString &str)
{
  str.rep->ref();
  release();
  rep = str.rep;

  return *this;
}

bool UString::is8Bit() const
{
  const UChar *u = data();
  const UChar *limit = u + size();
  while (u < limit) {
    if (u->uc > 0xFF)
      return false;
    ++u;
  }

  return true;
}

UChar UString::operator[](int pos) const
{
  if (pos >= size())
    return '\0';
  return data()[pos];
}

UCharReference UString::operator[](int pos)
{
  /* TODO: boundary check */
  return UCharReference(this, pos);
}

double UString::toDouble(bool tolerateTrailingJunk, bool tolerateEmptyString) const
{
  double d;

  // FIXME: If tolerateTrailingJunk is true, then we want to tolerate non-8-bit junk
  // after the number, so is8Bit is too strict a check.
  if (!is8Bit())
    return NaN;

  const char *c = ascii();

  // skip leading white space
  while (isspace(*c))
    c++;

  // empty string ?
  if (*c == '\0')
    return tolerateEmptyString ? 0.0 : NaN;

  // hex number ?
  if (*c == '0' && (*(c+1) == 'x' || *(c+1) == 'X')) {
    c++;
    d = 0.0;
    while (*(++c)) {
      if (*c >= '0' && *c <= '9')
	d = d * 16.0 + *c - '0';
      else if ((*c >= 'A' && *c <= 'F') || (*c >= 'a' && *c <= 'f'))
	d = d * 16.0 + (*c & 0xdf) - 'A' + 10.0;
      else
	break;
    }
  } else {
    // regular number ?
    char *end;
    d = kjs_strtod(c, &end);
    if ((d != 0.0 || end != c) && d != HUGE_VAL && d != -HUGE_VAL) {
      c = end;
    } else {
      // infinity ?
      d = 1.0;
      if (*c == '+')
	c++;
      else if (*c == '-') {
	d = -1.0;
	c++;
      }
      if (strncmp(c, "Infinity", 8) != 0)
	return NaN;
      d = d * Inf;
      c += 8;
    }
  }

  // allow trailing white space
  while (isspace(*c))
    c++;
  // don't allow anything after - unless tolerant=true
  if (!tolerateTrailingJunk && *c != '\0')
    d = NaN;

  return d;
}

double UString::toDouble(bool tolerateTrailingJunk) const
{
  return toDouble(tolerateTrailingJunk, true);
}

double UString::toDouble() const
{
  return toDouble(false, true);
}

unsigned long UString::toULong(bool *ok, bool tolerateEmptyString) const
{
  double d = toDouble(false, tolerateEmptyString);
  bool b = true;

  if (isNaN(d) || d != static_cast<unsigned long>(d)) {
    b = false;
    d = 0;
  }

  if (ok)
    *ok = b;

  return static_cast<unsigned long>(d);
}

unsigned long UString::toULong(bool *ok) const
{
  return toULong(ok, true);
}

uint32_t UString::toUInt32(bool *ok) const
{
  double d = toDouble();
  bool b = true;

  if (isNaN(d) || d != static_cast<uint32_t>(d)) {
    b = false;
    d = 0;
  }

  if (ok)
    *ok = b;

  return static_cast<uint32_t>(d);
}

uint32_t UString::toStrictUInt32(bool *ok) const
{
  if (ok)
    *ok = false;

  // Empty string is not OK.
  int len = rep->len;
  if (len == 0)
    return 0;
  const UChar *p = rep->dat;
  unsigned short c = p->unicode();

  // If the first digit is 0, only 0 itself is OK.
  if (c == '0') {
    if (len == 1 && ok)
      *ok = true;
    return 0;
  }
  
  // Convert to UInt32, checking for overflow.
  uint32_t i = 0;
  while (1) {
    // Process character, turning it into a digit.
    if (c < '0' || c > '9')
      return 0;
    const unsigned d = c - '0';
    
    // Multiply by 10, checking for overflow out of 32 bits.
    if (i > 0xFFFFFFFFU / 10)
      return 0;
    i *= 10;
    
    // Add in the digit, checking for overflow out of 32 bits.
    const unsigned max = 0xFFFFFFFFU - d;
    if (i > max)
        return 0;
    i += d;
    
    // Handle end of string.
    if (--len == 0) {
      if (ok)
        *ok = true;
      return i;
    }
    
    // Get next character.
    c = (++p)->unicode();
  }
}

// Rule from ECMA 15.2 about what an array index is.
// Must exactly match string form of an unsigned integer, and be less than 2^32 - 1.
unsigned UString::toArrayIndex(bool *ok) const
{
  unsigned i = toStrictUInt32(ok);
  if (i >= 0xFFFFFFFFU && ok)
    *ok = false;
  return i;
}

int UString::find(const UString &f, int pos) const
{
  int sz = size();
  int fsz = f.size();
  if (sz < fsz)
    return -1;
  if (pos < 0)
    pos = 0;
  if (fsz == 0)
    return pos;
  const UChar *end = data() + sz - fsz;
  long fsizeminusone = (fsz - 1) * sizeof(UChar);
  const UChar *fdata = f.data();
  for (const UChar *c = data() + pos; c <= end; c++)
    if (*c == *fdata && !memcmp(c + 1, fdata + 1, fsizeminusone))
      return (c-data());

  return -1;
}

int UString::find(UChar ch, int pos) const
{
  if (pos < 0)
    pos = 0;
  const UChar *end = data() + size();
  for (const UChar *c = data() + pos; c < end; c++)
    if (*c == ch)
      return (c-data());

  return -1;
}

int UString::rfind(const UString &f, int pos) const
{
  int sz = size();
  int fsz = f.size();
  if (sz < fsz)
    return -1;
  if (pos < 0)
    pos = 0;
  if (pos > sz - fsz)
    pos = sz - fsz;
  if (fsz == 0)
    return pos;
  long fsizeminusone = (fsz - 1) * sizeof(UChar);
  const UChar *fdata = f.data();
  for (const UChar *c = data() + pos; c >= data(); c--) {
    if (*c == *fdata && !memcmp(c + 1, fdata + 1, fsizeminusone))
      return (c-data());
  }

  return -1;
}

int UString::rfind(UChar ch, int pos) const
{
  if (isEmpty())
    return -1;
  if (pos + 1 >= size())
    pos = size() - 1;
  for (const UChar *c = data() + pos; c >= data(); c--) {
    if (*c == ch)
      return (c-data());
  }

  return -1;
}

UString UString::substr(int pos, int len) const
{
  if (pos < 0)
    pos = 0;
  else if (pos >= (int) size())
    pos = size();
  if (len < 0)
    len = size();
  if (pos + len >= (int) size())
    len = size() - pos;

  UChar *tmp = new UChar[len];
  memcpy(tmp, data()+pos, len * sizeof(UChar));
  UString result(tmp, len);
  delete [] tmp;

  return result;
}

void UString::attach(Rep *r)
{
  rep = r;
  rep->ref();
}

void UString::detach()
{
  if (rep->rc > 1) {
    int l = size();
    UChar *n = new UChar[l];
    memcpy(n, data(), l * sizeof(UChar));
    release();
    rep = Rep::create(n, l);
  }
}

void UString::release()
{
  rep->deref();
}

bool KJS::operator==(const UString& s1, const UString& s2)
{
  if (s1.rep->len != s2.rep->len)
    return false;

  return (memcmp(s1.rep->dat, s2.rep->dat,
		 s1.rep->len * sizeof(UChar)) == 0);
}

bool KJS::operator==(const UString& s1, const char *s2)
{
  if (s2 == 0) {
    return s1.isEmpty();
  }

  const UChar *u = s1.data();
  const UChar *uend = u + s1.size();
  while (u != uend && *s2) {
    if (u->uc != (unsigned char)*s2)
      return false;
    s2++;
    u++;
  }

  return u == uend && *s2 == 0;
}

bool KJS::operator<(const UString& s1, const UString& s2)
{
  const int l1 = s1.size();
  const int l2 = s2.size();
  const int lmin = l1 < l2 ? l1 : l2;
  const UChar *c1 = s1.data();
  const UChar *c2 = s2.data();
  int l = 0;
  while (l < lmin && *c1 == *c2) {
    c1++;
    c2++;
    l++;
  }
  if (l < lmin)
    return (c1->uc < c2->uc);

  return (l1 < l2);
}

int KJS::compare(const UString& s1, const UString& s2)
{
  const int l1 = s1.size();
  const int l2 = s2.size();
  const int lmin = l1 < l2 ? l1 : l2;
  const UChar *c1 = s1.data();
  const UChar *c2 = s2.data();
  int l = 0;
  while (l < lmin && *c1 == *c2) {
    c1++;
    c2++;
    l++;
  }
  if (l < lmin)
    return (c1->uc > c2->uc) ? 1 : -1;

  if (l1 == l2) {
    return 0;
  }
  return (l1 < l2) ? 1 : -1;
}

// Given a first byte, gives the length of the UTF-8 sequence it begins.
// Returns 0 for bytes that are not legal starts of UTF-8 sequences.
// Only allows sequences of up to 4 bytes, since that works for all Unicode characters (U-00000000 to U-0010FFFF).
int UTF8SequenceLength(char b0)
{
  if ((b0 & 0x80) == 0)
    return 1;
  if ((b0 & 0xC0) != 0xC0)
    return 0;
  if ((b0 & 0xE0) == 0xC0)
    return 2;
  if ((b0 & 0xF0) == 0xE0)
    return 3;
  if ((b0 & 0xF8) == 0xF0)
    return 4;
  return 0;
}

// Takes a null-terminated C-style string with a UTF-8 sequence in it and converts it to a character.
// Only allows Unicode characters (U-00000000 to U-0010FFFF).
// Returns -1 if the sequence is not valid (including presence of extra bytes).
int decodeUTF8Sequence(const char *sequence)
{
  // Handle 0-byte sequences (never valid).
  const unsigned char b0 = sequence[0];
  const int length = UTF8SequenceLength(b0);
  if (length == 0)
    return -1;

  // Handle 1-byte sequences (plain ASCII).
  const unsigned char b1 = sequence[1];
  if (length == 1) {
    if (b1)
      return -1;
    return b0;
  }

  // Handle 2-byte sequences.
  if ((b1 & 0xC0) != 0x80)
    return -1;
  const unsigned char b2 = sequence[2];
  if (length == 2) {
    if (b2)
      return -1;
    const int c = ((b0 & 0x1F) << 6) | (b1 & 0x3F);
    if (c < 0x80)
      return -1;
    return c;
  }

  // Handle 3-byte sequences.
  if ((b2 & 0xC0) != 0x80)
    return -1;
  const unsigned char b3 = sequence[3];
  if (length == 3) {
    if (b3)
      return -1;
    const int c = ((b0 & 0xF) << 12) | ((b1 & 0x3F) << 6) | (b2 & 0x3F);
    if (c < 0x800)
      return -1;
    // UTF-16 surrogates should never appear in UTF-8 data.
    if (c >= 0xD800 && c <= 0xDFFF)
      return -1;
    // Backwards BOM and U+FFFF should never appear in UTF-8 data.
    if (c == 0xFFFE || c == 0xFFFF)
      return -1;
    return c;
  }

  // Handle 4-byte sequences.
  if ((b3 & 0xC0) != 0x80)
    return -1;
  const unsigned char b4 = sequence[4];
  if (length == 4) {
    if (b4)
      return -1;
    const int c = ((b0 & 0x7) << 18) | ((b1 & 0x3F) << 12) | ((b2 & 0x3F) << 6) | (b3 & 0x3F);
    if (c < 0x10000 || c > 0x10FFFF)
      return -1;
    return c;
  }

  return -1;
}

CString UString::UTF8String() const
{
  // Allocate a buffer big enough to hold all the characters.
  const int length = size();
  const unsigned bufferSize = length * 3;
  char fixedSizeBuffer[1024];
  char *buffer;
  if (bufferSize > sizeof(fixedSizeBuffer)) {
    buffer = new char [bufferSize];
  } else {
    buffer = fixedSizeBuffer;
  }

  // Convert to runs of 8-bit characters.
  char *p = buffer;
  const UChar *d = data();
  for (int i = 0; i != length; ++i) {
    unsigned short c = d[i].unicode();
    if (c < 0x80) {
      *p++ = (char)c;
    } else if (c < 0x800) {
      *p++ = (char)((c >> 6) | 0xC0); // C0 is the 2-byte flag for UTF-8
      *p++ = (char)((c | 0x80) & 0xBF); // next 6 bits, with high bit set
    } else if (c >= 0xD800 && c <= 0xDBFF && i < length && d[i+1].uc >= 0xDC00 && d[i+2].uc <= 0xDFFF) {
      unsigned sc = 0x10000 + (((c & 0x3FF) << 10) | (d[i+1].uc & 0x3FF));
      *p++ = (char)((sc >> 18) | 0xF0); // F0 is the 4-byte flag for UTF-8
      *p++ = (char)(((sc >> 12) | 0x80) & 0xBF); // next 6 bits, with high bit set
      *p++ = (char)(((sc >> 6) | 0x80) & 0xBF); // next 6 bits, with high bit set
      *p++ = (char)((sc | 0x80) & 0xBF); // next 6 bits, with high bit set
      ++i;
    } else {
      *p++ = (char)((c >> 12) | 0xE0); // E0 is the 3-byte flag for UTF-8
      *p++ = (char)(((c >> 6) | 0x80) & 0xBF); // next 6 bits, with high bit set
      *p++ = (char)((c | 0x80) & 0xBF); // next 6 bits, with high bit set
    }
  }

  // Return the result as a C string.
  CString result(buffer, p - buffer);
  if (buffer != fixedSizeBuffer) {
    delete [] buffer;
  }
  return result;
}

struct StringOffset {
    int offset;
    int locationInOffsetsArray;
};

static int compareStringOffsets(const void *a, const void *b)
{
    const StringOffset *oa = static_cast<const StringOffset *>(a);
    const StringOffset *ob = static_cast<const StringOffset *>(b);
    
    if (oa->offset < ob->offset) {
        return -1;
    }
    if (oa->offset > ob->offset) {
        return +1;
    }
    return 0;
}

const int sortedOffsetsFixedBufferSize = 128;

static StringOffset *createSortedOffsetsArray(const int offsets[], int numOffsets,
    StringOffset sortedOffsetsFixedBuffer[sortedOffsetsFixedBufferSize])
{
    // Allocate the sorted offsets.
    StringOffset *sortedOffsets;
    if (numOffsets <= sortedOffsetsFixedBufferSize) {
        sortedOffsets = sortedOffsetsFixedBuffer;
    } else {
        sortedOffsets = new StringOffset [numOffsets];
    }

    // Copy offsets.
    for (int i = 0; i != numOffsets; ++i) {
        sortedOffsets[i].offset = offsets[i];
        sortedOffsets[i].locationInOffsetsArray = i;
    }

    // Sort them.
    qsort(sortedOffsets, numOffsets, sizeof(StringOffset), compareStringOffsets);

    return sortedOffsets;
}

// Note: This function assumes valid UTF-8.
// It can even go into an infinite loop if the passed in string is not valid UTF-8.
void convertUTF16OffsetsToUTF8Offsets(const char *s, int *offsets, int numOffsets)
{
    // Allocate buffer.
    StringOffset fixedBuffer[sortedOffsetsFixedBufferSize];
    StringOffset *sortedOffsets = createSortedOffsetsArray(offsets, numOffsets, fixedBuffer);

    // Walk through sorted offsets and string, adjusting all the offests.
    // Offsets that are off the ends of the string map to the edges of the string.
    int UTF16Offset = 0;
    const char *p = s;
    for (int oi = 0; oi != numOffsets; ++oi) {
        const int nextOffset = sortedOffsets[oi].offset;
        while (*p && UTF16Offset < nextOffset) {
            // Skip to the next character.
            const int sequenceLength = UTF8SequenceLength(*p);
            assert(sequenceLength >= 1 && sequenceLength <= 4);
            p += sequenceLength;
            // Characters that take a 4 byte sequence in UTF-8 take two bytes in UTF-16.
            UTF16Offset += sequenceLength < 4 ? 1 : 2;
        }
        offsets[sortedOffsets[oi].locationInOffsetsArray] = p - s;
    }

    // Free buffer.
    if (sortedOffsets != fixedBuffer) {
        delete [] sortedOffsets;
    }
}

// Note: This function assumes valid UTF-8.
// It can even go into an infinite loop if the passed in string is not valid UTF-8.
void convertUTF8OffsetsToUTF16Offsets(const char *s, int *offsets, int numOffsets)
{
    // Allocate buffer.
    StringOffset fixedBuffer[sortedOffsetsFixedBufferSize];
    StringOffset *sortedOffsets = createSortedOffsetsArray(offsets, numOffsets, fixedBuffer);

    // Walk through sorted offsets and string, adjusting all the offests.
    // Offsets that are off the end of the string map to the edges of the string.
    int UTF16Offset = 0;
    const char *p = s;
    for (int oi = 0; oi != numOffsets; ++oi) {
        const int nextOffset = sortedOffsets[oi].offset;
        while (*p && (p - s) < nextOffset) {
            // Skip to the next character.
            const int sequenceLength = UTF8SequenceLength(*p);
            assert(sequenceLength >= 1 && sequenceLength <= 4);
            p += sequenceLength;
            // Characters that take a 4 byte sequence in UTF-8 take two bytes in UTF-16.
            UTF16Offset += sequenceLength < 4 ? 1 : 2;
        }
        offsets[sortedOffsets[oi].locationInOffsetsArray] = UTF16Offset;
    }

    // Free buffer.
    if (sortedOffsets != fixedBuffer) {
        delete [] sortedOffsets;
    }
}

} // namespace KJS