mariadb/sql/sql_string.cc

/*
   Copyright (c) 2000, 2011, Oracle and/or its affiliates.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301  USA */

/* This file is originally from the mysql distribution. Coded by monty */

#ifdef USE_PRAGMA_IMPLEMENTATION
#pragma implementation				// gcc: Class implementation
#endif

#include <my_global.h>
#include <my_sys.h>
#include <m_string.h>
#include <m_ctype.h>
#include <mysql_com.h>

#include "sql_string.h"

/*****************************************************************************
** String functions
*****************************************************************************/

bool String::real_alloc(uint32 length)
{
  uint32 arg_length= ALIGN_SIZE(length + 1);
  DBUG_ASSERT(arg_length > length);
  if (arg_length <= length)
    return TRUE;                                 /* Overflow */
  str_length=0;
  if (Alloced_length < arg_length)
  {
    free();
    if (!(Ptr=(char*) my_malloc(arg_length,MYF(MY_WME |
                                               (thread_specific ?
                                                MY_THREAD_SPECIFIC : 0)))))
      return TRUE;
    Alloced_length=arg_length;
    alloced=1;
  }
  Ptr[0]=0;
  return FALSE;
}


/**
   Allocates a new buffer on the heap for this String.

   - If the String's internal buffer is privately owned and heap allocated,
     one of the following is performed.

     - If the requested length is greater than what fits in the buffer, a new
       buffer is allocated, data moved and the old buffer freed.

     - If the requested length is less or equal to what fits in the buffer, a
       null character is inserted at the appropriate position.

   - If the String does not keep a private buffer on the heap, such a buffer
     will be allocated and the string copied accoring to its length, as found
     in String::length().
 
   For C compatibility, the new string buffer is null terminated.

   @param alloc_length The requested string size in characters, excluding any
   null terminator.

   @retval false Either the copy operation is complete or, if the size of the
   new buffer is smaller than the currently allocated buffer (if one exists),
   no allocation occured.

   @retval true An error occured when attempting to allocate memory.
*/
bool String::realloc_raw(uint32 alloc_length)
{
  if (Alloced_length <= alloc_length)
  {
    char *new_ptr;
    uint32 len= ALIGN_SIZE(alloc_length+1);
    DBUG_ASSERT(len > alloc_length);
    if (len <= alloc_length)
      return TRUE;                                 /* Overflow */
    if (alloced)
    {
      if (!(new_ptr= (char*) my_realloc(Ptr,len,
                                        MYF(MY_WME |
                                            (thread_specific ?
                                             MY_THREAD_SPECIFIC : 0)))))
        return TRUE;				// Signal error
    }
    else if ((new_ptr= (char*) my_malloc(len,
                                         MYF(MY_WME |
                                             (thread_specific ?
                                              MY_THREAD_SPECIFIC : 0)))))
    {
      if (str_length > len - 1)
        str_length= 0;
      if (str_length)				// Avoid bugs in memcpy on AIX
	memcpy(new_ptr,Ptr,str_length);
      new_ptr[str_length]=0;
      alloced=1;
    }
    else
      return TRUE;			// Signal error
    Ptr= new_ptr;
    Alloced_length= len;
  }
  return FALSE;
}

bool String::set_int(longlong num, bool unsigned_flag, CHARSET_INFO *cs)
{
  uint l=20*cs->mbmaxlen+1;
  int base= unsigned_flag ? 10 : -10;

  if (alloc(l))
    return TRUE;
  str_length=(uint32) (cs->cset->longlong10_to_str)(cs,Ptr,l,base,num);
  str_charset=cs;
  return FALSE;
}

bool String::set_real(double num,uint decimals, CHARSET_INFO *cs)
{
  char buff[FLOATING_POINT_BUFFER];
  uint dummy_errors;
  size_t len;

  str_charset=cs;
  if (decimals >= NOT_FIXED_DEC)
  {
    len= my_gcvt(num, MY_GCVT_ARG_DOUBLE, sizeof(buff) - 1, buff, NULL);
    return copy(buff, len, &my_charset_latin1, cs, &dummy_errors);
  }
  len= my_fcvt(num, decimals, buff, NULL);
  return copy(buff, (uint32) len, &my_charset_latin1, cs,
              &dummy_errors);
}


bool String::copy()
{
  if (!alloced)
  {
    Alloced_length=0;				// Force realloc
    return realloc(str_length);
  }
  return FALSE;
}

/**
   Copies the internal buffer from str. If this String has a private heap
   allocated buffer where new data does not fit, a new buffer is allocated
   before copying and the old buffer freed. Character set information is also
   copied.
   
   @param str The string whose internal buffer is to be copied.
   
   @retval false Success.
   @retval true Memory allocation failed.
*/
bool String::copy(const String &str)
{
  if (alloc(str.str_length))
    return TRUE;
  str_length=str.str_length;
  bmove(Ptr,str.Ptr,str_length);		// May be overlapping
  Ptr[str_length]=0;
  str_charset=str.str_charset;
  return FALSE;
}

bool String::copy(const char *str,uint32 arg_length, CHARSET_INFO *cs)
{
  if (alloc(arg_length))
    return TRUE;
  if ((str_length=arg_length))
    memcpy(Ptr,str,arg_length);
  Ptr[arg_length]=0;
  str_charset=cs;
  return FALSE;
}


/*
  Checks that the source string can be just copied to the destination string
  without conversion.

  SYNPOSIS

  needs_conversion()
  arg_length		Length of string to copy.
  from_cs		Character set to copy from
  to_cs			Character set to copy to
  uint32 *offset	Returns number of unaligned characters.

  RETURN
   0  No conversion needed
   1  Either character set conversion or adding leading  zeros
      (e.g. for UCS-2) must be done

  NOTE
  to_cs may be NULL for "no conversion" if the system variable
  character_set_results is NULL.
*/

bool String::needs_conversion(uint32 arg_length,
			      CHARSET_INFO *from_cs,
			      CHARSET_INFO *to_cs,
			      uint32 *offset)
{
  *offset= 0;
  if (!to_cs ||
      (to_cs == &my_charset_bin) || 
      (to_cs == from_cs) ||
      my_charset_same(from_cs, to_cs) ||
      ((from_cs == &my_charset_bin) &&
       (!(*offset=(arg_length % to_cs->mbminlen)))))
    return FALSE;
  return TRUE;
}


/*
  Copy a multi-byte character sets with adding leading zeros.

  SYNOPSIS

  copy_aligned()
  str			String to copy
  arg_length		Length of string. This should NOT be dividable with
			cs->mbminlen.
  offset		arg_length % cs->mb_minlength
  cs			Character set for 'str'

  NOTES
    For real multi-byte, ascii incompatible charactser sets,
    like UCS-2, add leading zeros if we have an incomplete character.
    Thus, 
      SELECT _ucs2 0xAA 
    will automatically be converted into
      SELECT _ucs2 0x00AA

  RETURN
    0  ok
    1  error
*/

bool String::copy_aligned(const char *str,uint32 arg_length, uint32 offset,
			  CHARSET_INFO *cs)
{
  /* How many bytes are in incomplete character */
  offset= cs->mbminlen - offset; /* How many zeros we should prepend */
  DBUG_ASSERT(offset && offset != cs->mbminlen);

  uint32 aligned_length= arg_length + offset;
  if (alloc(aligned_length))
    return TRUE;
  
  /*
    Note, this is only safe for big-endian UCS-2.
    If we add little-endian UCS-2 sometimes, this code
    will be more complicated. But it's OK for now.
  */
  bzero((char*) Ptr, offset);
  memcpy(Ptr + offset, str, arg_length);
  Ptr[aligned_length]=0;
  /* str_length is always >= 0 as arg_length is != 0 */
  str_length= aligned_length;
  str_charset= cs;
  return FALSE;
}


bool String::set_or_copy_aligned(const char *str,uint32 arg_length,
				 CHARSET_INFO *cs)
{
  /* How many bytes are in incomplete character */
  uint32 offset= (arg_length % cs->mbminlen); 
  
  if (!offset) /* All characters are complete, just copy */
  {
    set(str, arg_length, cs);
    return FALSE;
  }
  return copy_aligned(str, arg_length, offset, cs);
}


/**
   Copies the character data into this String, with optional character set
   conversion.

   @return
   FALSE ok
   TRUE  Could not allocate result buffer

*/

bool String::copy(const char *str, uint32 arg_length,
		  CHARSET_INFO *from_cs, CHARSET_INFO *to_cs, uint *errors)
{
  uint32 offset;

  DBUG_ASSERT(!str || str != Ptr);
  
  if (!needs_conversion(arg_length, from_cs, to_cs, &offset))
  {
    *errors= 0;
    return copy(str, arg_length, to_cs);
  }
  if ((from_cs == &my_charset_bin) && offset)
  {
    *errors= 0;
    return copy_aligned(str, arg_length, offset, to_cs);
  }
  uint32 new_length= to_cs->mbmaxlen*arg_length;
  if (alloc(new_length))
    return TRUE;
  str_length=copy_and_convert((char*) Ptr, new_length, to_cs,
                              str, arg_length, from_cs, errors);
  str_charset=to_cs;
  return FALSE;
}


/*
  Set a string to the value of a latin1-string, keeping the original charset
  
  SYNOPSIS
    copy_or_set()
    str			String of a simple charset (latin1)
    arg_length		Length of string

  IMPLEMENTATION
    If string object is of a simple character set, set it to point to the
    given string.
    If not, make a copy and convert it to the new character set.

  RETURN
    0	ok
    1	Could not allocate result buffer

*/

bool String::set_ascii(const char *str, uint32 arg_length)
{
  if (str_charset->mbminlen == 1)
  {
    set(str, arg_length, str_charset);
    return 0;
  }
  uint dummy_errors;
  return copy(str, arg_length, &my_charset_latin1, str_charset, &dummy_errors);
}


/* This is used by mysql.cc */

bool String::fill(uint32 max_length,char fill_char)
{
  if (str_length > max_length)
    Ptr[str_length=max_length]=0;
  else
  {
    if (realloc(max_length))
      return TRUE;
    bfill(Ptr+str_length,max_length-str_length,fill_char);
    str_length=max_length;
  }
  return FALSE;
}

void String::strip_sp()
{
   while (str_length && my_isspace(str_charset,Ptr[str_length-1]))
    str_length--;
}

bool String::append(const String &s)
{
  if (s.length())
  {
    if (realloc_with_extra_if_needed(str_length+s.length()))
      return TRUE;
    memcpy(Ptr+str_length,s.ptr(),s.length());
    str_length+=s.length();
  }
  return FALSE;
}


/*
  Append an ASCII string to the a string of the current character set
*/

bool String::append(const char *s,uint32 arg_length)
{
  if (!arg_length)
    return FALSE;

  /*
    For an ASCII incompatible string, e.g. UCS-2, we need to convert
  */
  if (str_charset->mbminlen > 1)
  {
    uint32 add_length=arg_length * str_charset->mbmaxlen;
    uint dummy_errors;
    if (realloc_with_extra_if_needed(str_length+ add_length))
      return TRUE;
    str_length+= copy_and_convert(Ptr+str_length, add_length, str_charset,
				  s, arg_length, &my_charset_latin1,
                                  &dummy_errors);
    return FALSE;
  }

  /*
    For an ASCII compatinble string we can just append.
  */
  if (realloc_with_extra_if_needed(str_length+arg_length))
    return TRUE;
  memcpy(Ptr+str_length,s,arg_length);
  str_length+=arg_length;
  return FALSE;
}


/*
  Append a 0-terminated ASCII string
*/

bool String::append(const char *s)
{
  return append(s, (uint) strlen(s));
}



bool String::append_ulonglong(ulonglong val)
{
  if (realloc(str_length+MAX_BIGINT_WIDTH+2))
    return TRUE;
  char *end= (char*) longlong10_to_str(val, (char*) Ptr + str_length, 10);
  str_length= end - Ptr;
  return FALSE;
}

/*
  Append a string in the given charset to the string
  with character set recoding
*/

bool String::append(const char *s,uint32 arg_length, CHARSET_INFO *cs)
{
  uint32 offset;
  
  if (needs_conversion(arg_length, cs, str_charset, &offset))
  {
    uint32 add_length;
    if ((cs == &my_charset_bin) && offset)
    {
      DBUG_ASSERT(str_charset->mbminlen > offset);
      offset= str_charset->mbminlen - offset; // How many characters to pad
      add_length= arg_length + offset;
      if (realloc(str_length + add_length))
        return TRUE;
      bzero((char*) Ptr + str_length, offset);
      memcpy(Ptr + str_length + offset, s, arg_length);
      str_length+= add_length;
      return FALSE;
    }

    add_length= arg_length / cs->mbminlen * str_charset->mbmaxlen;
    uint dummy_errors;
    if (realloc_with_extra_if_needed(str_length + add_length)) 
      return TRUE;
    str_length+= copy_and_convert(Ptr+str_length, add_length, str_charset,
				  s, arg_length, cs, &dummy_errors);
  }
  else
  {
    if (realloc_with_extra_if_needed(str_length + arg_length)) 
      return TRUE;
    memcpy(Ptr + str_length, s, arg_length);
    str_length+= arg_length;
  }
  return FALSE;
}

bool String::append(IO_CACHE* file, uint32 arg_length)
{
  if (realloc_with_extra_if_needed(str_length+arg_length))
    return TRUE;
  if (my_b_read(file, (uchar*) Ptr + str_length, arg_length))
  {
    shrink(str_length);
    return TRUE;
  }
  str_length+=arg_length;
  return FALSE;
}


/**
  Append a parenthesized number to String.
  Used in various pieces of SHOW related code.

  @param nr     Number
  @param radix  Radix, optional parameter, 10 by default.
*/
bool String::append_parenthesized(long nr, int radix)
{
  char buff[64], *end;
  buff[0]= '(';
  end= int10_to_str(nr, buff + 1, radix);
  *end++ = ')';
  return append(buff, (uint) (end - buff));
}


bool String::append_with_prefill(const char *s,uint32 arg_length,
		 uint32 full_length, char fill_char)
{
  int t_length= arg_length > full_length ? arg_length : full_length;

  if (realloc_with_extra_if_needed(str_length + t_length))
    return TRUE;
  t_length= full_length - arg_length;
  if (t_length > 0)
  {
    bfill(Ptr+str_length, t_length, fill_char);
    str_length=str_length + t_length;
  }
  append(s, arg_length);
  return FALSE;
}

uint32 String::numchars()
{
  return str_charset->cset->numchars(str_charset, Ptr, Ptr+str_length);
}

int String::charpos(longlong i,uint32 offset)
{
  if (i <= 0)
    return (int)i;
  return (int)str_charset->cset->charpos(str_charset,Ptr+offset,Ptr+str_length,(size_t)i);
}

int String::strstr(const String &s,uint32 offset)
{
  if (s.length()+offset <= str_length)
  {
    if (!s.length())
      return ((int) offset);	// Empty string is always found

    register const char *str = Ptr+offset;
    register const char *search=s.ptr();
    const char *end=Ptr+str_length-s.length()+1;
    const char *search_end=s.ptr()+s.length();
skip:
    while (str != end)
    {
      if (*str++ == *search)
      {
	register char *i,*j;
	i=(char*) str; j=(char*) search+1;
	while (j != search_end)
	  if (*i++ != *j++) goto skip;
	return (int) (str-Ptr) -1;
      }
    }
  }
  return -1;
}

/*
** Search string from end. Offset is offset to the end of string
*/

int String::strrstr(const String &s,uint32 offset)
{
  if (s.length() <= offset && offset <= str_length)
  {
    if (!s.length())
      return offset;				// Empty string is always found
    register const char *str = Ptr+offset-1;
    register const char *search=s.ptr()+s.length()-1;

    const char *end=Ptr+s.length()-2;
    const char *search_end=s.ptr()-1;
skip:
    while (str != end)
    {
      if (*str-- == *search)
      {
	register char *i,*j;
	i=(char*) str; j=(char*) search-1;
	while (j != search_end)
	  if (*i-- != *j--) goto skip;
	return (int) (i-Ptr) +1;
      }
    }
  }
  return -1;
}

/*
  Replace substring with string
  If wrong parameter or not enough memory, do nothing
*/

bool String::replace(uint32 offset,uint32 arg_length,const String &to)
{
  return replace(offset,arg_length,to.ptr(),to.length());
}

bool String::replace(uint32 offset,uint32 arg_length,
                     const char *to, uint32 to_length)
{
  long diff = (long) to_length-(long) arg_length;
  if (offset+arg_length <= str_length)
  {
    if (diff < 0)
    {
      if (to_length)
	memcpy(Ptr+offset,to,to_length);
      bmove(Ptr+offset+to_length,Ptr+offset+arg_length,
	    str_length-offset-arg_length);
    }
    else
    {
      if (diff)
      {
	if (realloc_with_extra_if_needed(str_length+(uint32) diff))
	  return TRUE;
	bmove_upp((uchar*) Ptr+str_length+diff, (uchar*) Ptr+str_length,
		  str_length-offset-arg_length);
      }
      if (to_length)
	memcpy(Ptr+offset,to,to_length);
    }
    str_length+=(uint32) diff;
  }
  return FALSE;
}


// added by Holyfoot for "geometry" needs
int String::reserve(uint32 space_needed, uint32 grow_by)
{
  if (Alloced_length < str_length + space_needed)
  {
    if (realloc(Alloced_length + max(space_needed, grow_by) - 1))
      return TRUE;
  }
  return FALSE;
}

void String::qs_append(const char *str, uint32 len)
{
  memcpy(Ptr + str_length, str, len + 1);
  str_length += len;
}

void String::qs_append(double d)
{
  char *buff = Ptr + str_length;
  str_length+= my_gcvt(d, MY_GCVT_ARG_DOUBLE, FLOATING_POINT_BUFFER - 1, buff,
                       NULL);
}

void String::qs_append(double *d)
{
  double ld;
  float8get(ld, (char*) d);
  qs_append(ld);
}

void String::qs_append(int i)
{
  char *buff= Ptr + str_length;
  char *end= int10_to_str(i, buff, -10);
  str_length+= (int) (end-buff);
}

void String::qs_append(ulonglong i)
{
  char *buff= Ptr + str_length;
  char *end= longlong10_to_str(i, buff,10);
  str_length+= (int) (end-buff);
}

/*
  Compare strings according to collation, without end space.

  SYNOPSIS
    sortcmp()
    s		First string
    t		Second string
    cs		Collation

  NOTE:
    Normally this is case sensitive comparison

  RETURN
  < 0	s < t
  0	s == t
  > 0	s > t
*/


int sortcmp(const String *s,const String *t, CHARSET_INFO *cs)
{
 return cs->coll->strnncollsp(cs,
                              (uchar *) s->ptr(),s->length(),
                              (uchar *) t->ptr(),t->length(), 0);
}


/*
  Compare strings byte by byte. End spaces are also compared.

  SYNOPSIS
    stringcmp()
    s		First string
    t		Second string

  NOTE:
    Strings are compared as a stream of uchars

  RETURN
  < 0	s < t
  0	s == t
  > 0	s > t
*/


int stringcmp(const String *s,const String *t)
{
  uint32 s_len=s->length(),t_len=t->length(),len=min(s_len,t_len);
  int cmp= memcmp(s->ptr(), t->ptr(), len);
  return (cmp) ? cmp : (int) (s_len - t_len);
}


String *copy_if_not_alloced(String *to,String *from,uint32 from_length)
{
  if (from->Alloced_length >= from_length)
    return from;
  if (from->alloced || !to || from == to)
  {
    (void) from->realloc(from_length);
    return from;
  }
  if (to->realloc(from_length))
    return from;				// Actually an error
  if ((to->str_length=min(from->str_length,from_length)))
    memcpy(to->Ptr,from->Ptr,to->str_length);
  to->str_charset=from->str_charset;
  return to;
}


/****************************************************************************
  Help functions
****************************************************************************/



/*
  Optimized for quick copying of ASCII characters in the range 0x00..0x7F.
*/
uint32
copy_and_convert(char *to, uint32 to_length, CHARSET_INFO *to_cs, 
                 const char *from, uint32 from_length, CHARSET_INFO *from_cs,
                 uint *errors)
{
  /*
    If any of the character sets is not ASCII compatible,
    immediately switch to slow mb_wc->wc_mb method.
  */
  if ((to_cs->state | from_cs->state) & MY_CS_NONASCII)
    return copy_and_convert_extended(to, to_length, to_cs,
                                     from, from_length, from_cs, errors);

  uint32 length= min(to_length, from_length), length2= length;

#if defined(__i386__)
  /*
    Special loop for i386, it allows to refer to a
    non-aligned memory block as UINT32, which makes
    it possible to copy four bytes at once. This
    gives about 10% performance improvement comparing
    to byte-by-byte loop.
  */
  for ( ; length >= 4; length-= 4, from+= 4, to+= 4)
  {
    if ((*(uint32*)from) & 0x80808080)
      break;
    *((uint32*) to)= *((const uint32*) from);
  }
#endif

  for (; ; *to++= *from++, length--)
  {
    if (!length)
    {
      *errors= 0;
      return length2;
    }
    if (*((unsigned char*) from) > 0x7F) /* A non-ASCII character */
    {
      uint32 copied_length= length2 - length;
      to_length-= copied_length;
      from_length-= copied_length;
      return copied_length + copy_and_convert_extended(to, to_length,
                                                       to_cs,
                                                       from, from_length,
                                                       from_cs,
                                                       errors);
    }
  }

  DBUG_ASSERT(FALSE); // Should never get to here
  return 0;           // Make compiler happy
}


/**
  Copy string with HEX-encoding of "bad" characters.

  @details This functions copies the string pointed by "src"
  to the string pointed by "dst". Not more than "srclen" bytes
  are read from "src". Any sequences of bytes representing
  a not-well-formed substring (according to cs) are hex-encoded,
  and all well-formed substrings (according to cs) are copied as is.
  Not more than "dstlen" bytes are written to "dst". The number 
  of bytes written to "dst" is returned.
  
   @param      cs       character set pointer of the destination string
   @param[out] dst      destination string
   @param      dstlen   size of dst
   @param      src      source string
   @param      srclen   length of src

   @retval     result length
*/

size_t
my_copy_with_hex_escaping(CHARSET_INFO *cs,
                          char *dst, size_t dstlen,
                          const char *src, size_t srclen)
{
  const char *srcend= src + srclen;
  char *dst0= dst;

  for ( ; src < srcend ; )
  {
    size_t chlen;
    if ((chlen= my_ismbchar(cs, src, srcend)))
    {
      if (dstlen < chlen)
        break; /* purecov: inspected */
      memcpy(dst, src, chlen);
      src+= chlen;
      dst+= chlen;
      dstlen-= chlen;
    }
    else if (*src & 0x80)
    {
      if (dstlen < 4)
        break; /* purecov: inspected */
      *dst++= '\\';
      *dst++= 'x';
      *dst++= _dig_vec_upper[((unsigned char) *src) >> 4];
      *dst++= _dig_vec_upper[((unsigned char) *src) & 15];
      src++;
      dstlen-= 4;
    }
    else
    {
      if (dstlen < 1)
        break; /* purecov: inspected */
      *dst++= *src++;
      dstlen--;
    }
  }
  return dst - dst0;
}


/*
  copy a string,
  with optional character set conversion,
  with optional left padding (for binary -> UCS2 conversion)
  
  SYNOPSIS
    well_formed_copy_nchars()
    to			     Store result here
    to_length                Maxinum length of "to" string
    to_cs		     Character set of "to" string
    from		     Copy from here
    from_length		     Length of from string
    from_cs		     From character set
    nchars                   Copy not more that nchars characters
    well_formed_error_pos    Return position when "from" is not well formed
                             or NULL otherwise.
    cannot_convert_error_pos Return position where a not convertable
                             character met, or NULL otherwise.
    from_end_pos             Return position where scanning of "from"
                             string stopped.
  NOTES

  RETURN
    length of bytes copied to 'to'
*/


uint32
well_formed_copy_nchars(CHARSET_INFO *to_cs,
                        char *to, uint to_length,
                        CHARSET_INFO *from_cs,
                        const char *from, uint from_length,
                        uint nchars,
                        const char **well_formed_error_pos,
                        const char **cannot_convert_error_pos,
                        const char **from_end_pos)
{
  uint res;

  if ((to_cs == &my_charset_bin) || 
      (from_cs == &my_charset_bin) ||
      (to_cs == from_cs) ||
      my_charset_same(from_cs, to_cs))
  {
    if (to_length < to_cs->mbminlen || !nchars)
    {
      *from_end_pos= from;
      *cannot_convert_error_pos= NULL;
      *well_formed_error_pos= NULL;
      return 0;
    }

    if (to_cs == &my_charset_bin)
    {
      res= min(min(nchars, to_length), from_length);
      memmove(to, from, res);
      *from_end_pos= from + res;
      *well_formed_error_pos= NULL;
      *cannot_convert_error_pos= NULL;
    }
    else
    {
      int well_formed_error;
      uint from_offset;

      if ((from_offset= (from_length % to_cs->mbminlen)) &&
          (from_cs == &my_charset_bin))
      {
        /*
          Copying from BINARY to UCS2 needs to prepend zeros sometimes:
          INSERT INTO t1 (ucs2_column) VALUES (0x01);
          0x01 -> 0x0001
        */
        uint pad_length= to_cs->mbminlen - from_offset;
        bzero(to, pad_length);
        memmove(to + pad_length, from, from_offset);
        /*
          In some cases left zero-padding can create an incorrect character.
          For example:
            INSERT INTO t1 (utf32_column) VALUES (0x110000);
          We'll pad the value to 0x00110000, which is a wrong UTF32 sequence!
          The valid characters range is limited to 0x00000000..0x0010FFFF.
          
          Make sure we didn't pad to an incorrect character.
        */
        if (to_cs->cset->well_formed_len(to_cs,
                                         to, to + to_cs->mbminlen, 1,
                                         &well_formed_error) !=
                                         to_cs->mbminlen)
        {
          *from_end_pos= *well_formed_error_pos= from;
          *cannot_convert_error_pos= NULL;
          return 0;
        }
        nchars--;
        from+= from_offset;
        from_length-= from_offset;
        to+= to_cs->mbminlen;
        to_length-= to_cs->mbminlen;
      }

      set_if_smaller(from_length, to_length);
      res= to_cs->cset->well_formed_len(to_cs, from, from + from_length,
                                        nchars, &well_formed_error);
      memmove(to, from, res);
      *from_end_pos= from + res;
      *well_formed_error_pos= well_formed_error ? from + res : NULL;
      *cannot_convert_error_pos= NULL;
      if (from_offset)
        res+= to_cs->mbminlen;
    }
  }
  else
  {
    int cnvres;
    my_wc_t wc;
    my_charset_conv_mb_wc mb_wc= from_cs->cset->mb_wc;
    my_charset_conv_wc_mb wc_mb= to_cs->cset->wc_mb;
    const uchar *from_end= (const uchar*) from + from_length;
    uchar *to_end= (uchar*) to + to_length;
    char *to_start= to;
    *well_formed_error_pos= NULL;
    *cannot_convert_error_pos= NULL;

    for ( ; nchars; nchars--)
    {
      const char *from_prev= from;
      if ((cnvres= (*mb_wc)(from_cs, &wc, (uchar*) from, from_end)) > 0)
        from+= cnvres;
      else if (cnvres == MY_CS_ILSEQ)
      {
        if (!*well_formed_error_pos)
          *well_formed_error_pos= from;
        from++;
        wc= '?';
      }
      else if (cnvres > MY_CS_TOOSMALL)
      {
        /*
          A correct multibyte sequence detected
          But it doesn't have Unicode mapping.
        */
        if (!*cannot_convert_error_pos)
          *cannot_convert_error_pos= from;
        from+= (-cnvres);
        wc= '?';
      }
      else
        break;  // Not enough characters

outp:
      if ((cnvres= (*wc_mb)(to_cs, wc, (uchar*) to, to_end)) > 0)
        to+= cnvres;
      else if (cnvres == MY_CS_ILUNI && wc != '?')
      {
        if (!*cannot_convert_error_pos)
          *cannot_convert_error_pos= from_prev;
        wc= '?';
        goto outp;
      }
      else
      {
        from= from_prev;
        break;
      }
    }
    *from_end_pos= from;
    res= (uint) (to - to_start);
  }
  return (uint32) res;
}



/*
  Append characters to a single-quoted string '...', escaping special
  characters as necessary.
  Does not add the enclosing quotes, this is left up to caller.
*/
void String::append_for_single_quote(const char *st, uint len)
{
  const char *end= st+len;
  for (; st < end; st++)
  {
    uchar c= *st;
    switch (c)
    {
    case '\\':
      append(STRING_WITH_LEN("\\\\"));
      break;
    case '\0':
      append(STRING_WITH_LEN("\\0"));
      break;
    case '\'':
      append(STRING_WITH_LEN("\\'"));
      break;
    case '\n':
      append(STRING_WITH_LEN("\\n"));
      break;
    case '\r':
      append(STRING_WITH_LEN("\\r"));
      break;
    case '\032': // Ctrl-Z
      append(STRING_WITH_LEN("\\Z"));
      break;
    default:
      append(c);
    }
  }
}

void String::print(String *str)
{
  str->append_for_single_quote(Ptr, str_length);
}

/*
  Exchange state of this object and argument.

  SYNOPSIS
    String::swap()

  RETURN
    Target string will contain state of this object and vice versa.
*/

void String::swap(String &s)
{
  swap_variables(char *, Ptr, s.Ptr);
  swap_variables(uint32, str_length, s.str_length);
  swap_variables(uint32, Alloced_length, s.Alloced_length);
  swap_variables(bool, alloced, s.alloced);
  swap_variables(CHARSET_INFO*, str_charset, s.str_charset);
}


/**
  Convert string to printable ASCII string

  @details This function converts input string "from" replacing non-ASCII bytes
  with hexadecimal sequences ("\xXX") optionally appending "..." to the end of
  the resulting string.
  This function used in the ER_TRUNCATED_WRONG_VALUE_FOR_FIELD error messages,
  e.g. when a string cannot be converted to a result charset.


  @param    to          output buffer
  @param    to_len      size of the output buffer (8 bytes or greater)
  @param    from        input string
  @param    from_len    size of the input string
  @param    from_cs     input charset
  @param    nbytes      maximal number of bytes to convert (from_len if 0)

  @return   number of bytes in the output string
*/

uint convert_to_printable(char *to, size_t to_len,
                          const char *from, size_t from_len,
                          CHARSET_INFO *from_cs, size_t nbytes /*= 0*/)
{
  /* needs at least 8 bytes for '\xXX...' and zero byte */
  DBUG_ASSERT(to_len >= 8);

  char *t= to;
  char *t_end= to + to_len - 1; // '- 1' is for the '\0' at the end
  const char *f= from;
  const char *f_end= from + (nbytes ? min(from_len, nbytes) : from_len);
  char *dots= to; // last safe place to append '...'

  if (!f || t == t_end)
    return 0;

  for (; t < t_end && f < f_end; f++)
  {
    /*
      If the source string is ASCII compatible (mbminlen==1)
      and the source character is in ASCII printable range (0x20..0x7F),
      then display the character as is.
      
      Otherwise, if the source string is not ASCII compatible (e.g. UCS2),
      or the source character is not in the printable range,
      then print the character using HEX notation.
    */
    if (((unsigned char) *f) >= 0x20 &&
        ((unsigned char) *f) <= 0x7F &&
        from_cs->mbminlen == 1)
    {
      *t++= *f;
    }
    else
    {
      if (t_end - t < 4) // \xXX
        break;
      *t++= '\\';
      *t++= 'x';
      *t++= _dig_vec_upper[((unsigned char) *f) >> 4];
      *t++= _dig_vec_upper[((unsigned char) *f) & 0x0F];
    }
    if (t_end - t >= 3) // '...'
      dots= t;
  }
  if (f < from + from_len)
    memcpy(dots, STRING_WITH_LEN("...\0"));
  else
    *t= '\0';
  return t - to;
}