guniprop.c

/* guniprop.c - Unicode character properties.
 *
 * Copyright (C) 1999 Tom Tromey
 * Copyright (C) 2000 Red Hat, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#include "glib.h"
#include "gunichartables.h"

#include <config.h>

#include <stddef.h>
#include <string.h>
#include <locale.h>

#define ATTTABLE(Page, Char) \
  ((attr_table[Page] == G_UNICODE_MAX_TABLE_INDEX) ? 0 : (attr_data[attr_table[Page]][Char]))

/* We cheat a bit and cast type values to (char *).  We detect these
   using the &0xff trick.  */
#define TTYPE(Page, Char) \
  ((type_table[Page] >= G_UNICODE_MAX_TABLE_INDEX) \
   ? (type_table[Page] - G_UNICODE_MAX_TABLE_INDEX) \
   : (type_data[type_table[Page]][Char]))


#define TYPE(Char) (((Char) > (G_UNICODE_LAST_CHAR)) ? G_UNICODE_UNASSIGNED : TTYPE ((Char) >> 8, (Char) & 0xff))

#define ISDIGIT(Type) ((Type) == G_UNICODE_DECIMAL_NUMBER	\
		       || (Type) == G_UNICODE_LETTER_NUMBER	\
		       || (Type) == G_UNICODE_OTHER_NUMBER)

#define ISALPHA(Type) ((Type) == G_UNICODE_LOWERCASE_LETTER	\
		       || (Type) == G_UNICODE_UPPERCASE_LETTER	\
		       || (Type) == G_UNICODE_TITLECASE_LETTER	\
		       || (Type) == G_UNICODE_MODIFIER_LETTER	\
		       || (Type) == G_UNICODE_OTHER_LETTER)

#define ISMARK(Type) ((Type) == G_UNICODE_NON_SPACING_MARK ||	\
		      (Type) == G_UNICODE_COMBINING_MARK ||	\
		      (Type) == G_UNICODE_ENCLOSING_MARK)
		      

/**
 * g_unichar_isalnum:
 * @c: a Unicode character
 * 
 * Determines whether a character is alphanumeric.
 * Given some UTF-8 text, obtain a character value
 * with g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is an alphanumeric character
 **/
gboolean
g_unichar_isalnum (gunichar c)
{
  int t = TYPE (c);
  return ISDIGIT (t) || ISALPHA (t);
}

/**
 * g_unichar_isalpha:
 * @c: a Unicode character
 * 
 * Determines whether a character is alphabetic (i.e. a letter).
 * Given some UTF-8 text, obtain a character value with
 * g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is an alphabetic character
 **/
gboolean
g_unichar_isalpha (gunichar c)
{
  int t = TYPE (c);
  return ISALPHA (t);
}


/**
 * g_unichar_iscntrl:
 * @c: a Unicode character
 * 
 * Determines whether a character is a control character.
 * Given some UTF-8 text, obtain a character value with
 * g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is a control character
 **/
gboolean
g_unichar_iscntrl (gunichar c)
{
  return TYPE (c) == G_UNICODE_CONTROL;
}

/**
 * g_unichar_isdigit:
 * @c: a Unicode character
 * 
 * Determines whether a character is numeric (i.e. a digit).  This
 * covers ASCII 0-9 and also digits in other languages/scripts.  Given
 * some UTF-8 text, obtain a character value with g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is a digit
 **/
gboolean
g_unichar_isdigit (gunichar c)
{
  return TYPE (c) == G_UNICODE_DECIMAL_NUMBER;
}


/**
 * g_unichar_isgraph:
 * @c: a Unicode character
 * 
 * Determines whether a character is printable and not a space
 * (returns %FALSE for control characters, format characters, and
 * spaces). g_unichar_isprint() is similar, but returns %TRUE for
 * spaces. Given some UTF-8 text, obtain a character value with
 * g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is printable unless it's a space
 **/
gboolean
g_unichar_isgraph (gunichar c)
{
  int t = TYPE (c);
  return (t != G_UNICODE_CONTROL
	  && t != G_UNICODE_FORMAT
	  && t != G_UNICODE_UNASSIGNED
	  && t != G_UNICODE_PRIVATE_USE
	  && t != G_UNICODE_SURROGATE
	  && t != G_UNICODE_SPACE_SEPARATOR);
}

/**
 * g_unichar_islower:
 * @c: a Unicode character
 * 
 * Determines whether a character is a lowercase letter.
 * Given some UTF-8 text, obtain a character value with
 * g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is a lowercase letter
 **/
gboolean
g_unichar_islower (gunichar c)
{
  return TYPE (c) == G_UNICODE_LOWERCASE_LETTER;
}


/**
 * g_unichar_isprint:
 * @c: a Unicode character
 * 
 * Determines whether a character is printable.
 * Unlike g_unichar_isgraph(), returns %TRUE for spaces.
 * Given some UTF-8 text, obtain a character value with
 * g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is printable
 **/
gboolean
g_unichar_isprint (gunichar c)
{
  int t = TYPE (c);
  return (t != G_UNICODE_CONTROL
	  && t != G_UNICODE_FORMAT
	  && t != G_UNICODE_UNASSIGNED
	  && t != G_UNICODE_PRIVATE_USE
	  && t != G_UNICODE_SURROGATE);
}

/**
 * g_unichar_ispunct:
 * @c: a Unicode character
 * 
 * Determines whether a character is punctuation or a symbol.
 * Given some UTF-8 text, obtain a character value with
 * g_utf8_get_char().
 * 
 * Return value: %TRUE if @c is a punctuation or symbol character
 **/
gboolean
g_unichar_ispunct (gunichar c)
{
  int t = TYPE (c);
  return (t == G_UNICODE_CONNECT_PUNCTUATION || t == G_UNICODE_DASH_PUNCTUATION
	  || t == G_UNICODE_CLOSE_PUNCTUATION || t == G_UNICODE_FINAL_PUNCTUATION
	  || t == G_UNICODE_INITIAL_PUNCTUATION || t == G_UNICODE_OTHER_PUNCTUATION
	  || t == G_UNICODE_OPEN_PUNCTUATION || t == G_UNICODE_CURRENCY_SYMBOL
	  || t == G_UNICODE_MODIFIER_SYMBOL || t == G_UNICODE_MATH_SYMBOL
	  || t == G_UNICODE_OTHER_SYMBOL);
}

/**
 * g_unichar_isspace:
 * @c: a Unicode character
 * 
 * Determines whether a character is a space, tab, or line separator
 * (newline, carriage return, etc.).  Given some UTF-8 text, obtain a
 * character value with g_utf8_get_char().
 *
 * (Note: don't use this to do word breaking; you have to use
 * Pango or equivalent to get word breaking right, the algorithm
 * is fairly complex.)
 *  
 * Return value: %TRUE if @c is a punctuation character
 **/
gboolean
g_unichar_isspace (gunichar c)
{
  switch (c)
    {
      /* special-case these since Unicode thinks they are not spaces */
    case '\t':
    case '\n':
    case '\r':
    case '\f':
      return TRUE;
      break;
      
    default:
      {
        int t = TYPE (c);
        return (t == G_UNICODE_SPACE_SEPARATOR || t == G_UNICODE_LINE_SEPARATOR
                || t == G_UNICODE_PARAGRAPH_SEPARATOR);
      }
      break;
    }
}

/**
 * g_unichar_isupper:
 * @c: a Unicode character
 * 
 * Determines if a character is uppercase.
 * 
 * Return value: %TRUE if @c is an uppercase character
 **/
gboolean
g_unichar_isupper (gunichar c)
{
  return TYPE (c) == G_UNICODE_UPPERCASE_LETTER;
}

/**
 * g_unichar_istitle:
 * @c: a Unicode character
 * 
 * Determines if a character is titlecase. Some characters in
 * Unicode which are composites, such as the DZ digraph
 * have three case variants instead of just two. The titlecase
 * form is used at the beginning of a word where only the
 * first letter is capitalized. The titlecase form of the DZ
 * digraph is U+01F2 LATIN CAPITAL LETTTER D WITH SMALL LETTER Z.
 * 
 * Return value: %TRUE if the character is titlecase
 **/
gboolean
g_unichar_istitle (gunichar c)
{
  unsigned int i;
  for (i = 0; i < G_N_ELEMENTS (title_table); ++i)
    if (title_table[i][0] == c)
      return 1;
  return 0;
}

/**
 * g_unichar_isxdigit:
 * @c: a Unicode character.
 * 
 * Determines if a character is a hexidecimal digit.
 * 
 * Return value: %TRUE if the character is a hexadecimal digit
 **/
gboolean
g_unichar_isxdigit (gunichar c)
{
  int t = TYPE (c);
  return ((c >= 'a' && c <= 'f')
	  || (c >= 'A' && c <= 'F')
	  || ISDIGIT (t));
}

/**
 * g_unichar_isdefined:
 * @c: a Unicode character
 * 
 * Determines if a given character is assigned in the Unicode
 * standard.
 *
 * Return value: %TRUE if the character has an assigned value
 **/
gboolean
g_unichar_isdefined (gunichar c)
{
  int t = TYPE (c);
  return t != G_UNICODE_UNASSIGNED;
}

/**
 * g_unichar_iswide:
 * @c: a Unicode character
 * 
 * Determines if a character is typically rendered in a double-width
 * cell.
 * 
 * Return value: %TRUE if the character is wide
 **/
/* This function stolen from Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk>.  */
gboolean
g_unichar_iswide (gunichar c)
{
  if (c < 0x1100)
    return 0;

  return ((c >= 0x1100 && c <= 0x115f)	   /* Hangul Jamo */
	  || (c >= 0x2e80 && c <= 0xa4cf && (c & ~0x0011) != 0x300a &&
	      c != 0x303f)		   /* CJK ... Yi */
	  || (c >= 0xac00 && c <= 0xd7a3)  /* Hangul Syllables */
	  || (c >= 0xf900 && c <= 0xfaff)  /* CJK Compatibility Ideographs */
	  || (c >= 0xfe30 && c <= 0xfe6f)  /* CJK Compatibility Forms */
	  || (c >= 0xff00 && c <= 0xff5f)  /* Fullwidth Forms */
	  || (c >= 0xffe0 && c <= 0xffe6));
}

/**
 * g_unichar_toupper:
 * @c: a Unicode character
 * 
 * Converts a character to uppercase.
 * 
 * Return value: the result of converting @c to uppercase.
 *               If @c is not an lowercase or titlecase character,
 *               @c is returned unchanged.
 **/
gunichar
g_unichar_toupper (gunichar c)
{
  int t = TYPE (c);
  if (t == G_UNICODE_LOWERCASE_LETTER)
    {
      gunichar val = ATTTABLE (c >> 8, c & 0xff);
      if (val >= 0xd800 && val < 0xdc00)
	{
	  const guchar *p = special_case_table[val - 0xd800];
	  return p[0] * 256 + p[1];
	}
      else
	return val;
    }
  else if (t == G_UNICODE_TITLECASE_LETTER)
    {
      unsigned int i;
      for (i = 0; i < G_N_ELEMENTS (title_table); ++i)
	{
	  if (title_table[i][0] == c)
	    return title_table[i][1];
	}
    }
  return c;
}

/**
 * g_unichar_tolower:
 * @c: a Unicode character.
 * 
 * Converts a character to lower case.
 * 
 * Return value: the result of converting @c to lower case.
 *               If @c is not an upperlower or titlecase character,
 *               @c is returned unchanged.
 **/
gunichar
g_unichar_tolower (gunichar c)
{
  int t = TYPE (c);
  if (t == G_UNICODE_UPPERCASE_LETTER)
    {
      gunichar val = ATTTABLE (c >> 8, c & 0xff);
      if (val >= 0xd800 && val < 0xdc00)
	{
	  const guchar *p = special_case_table[val - 0xd800];
	  return p[0] * 256 + p[1];
	}
      else
	return val;
    }
  else if (t == G_UNICODE_TITLECASE_LETTER)
    {
      unsigned int i;
      for (i = 0; i < G_N_ELEMENTS (title_table); ++i)
	{
	  if (title_table[i][0] == c)
	    return title_table[i][2];
	}
    }
  return c;
}

/**
 * g_unichar_totitle:
 * @c: a Unicode character
 * 
 * Converts a character to the titlecase.
 * 
 * Return value: the result of converting @c to titlecase.
 *               If @c is not an uppercase or lowercase character,
 *               @c is returned unchanged.
 **/
gunichar
g_unichar_totitle (gunichar c)
{
  unsigned int i;
  for (i = 0; i < G_N_ELEMENTS (title_table); ++i)
    {
      if (title_table[i][0] == c || title_table[i][1] == c
	  || title_table[i][2] == c)
	return title_table[i][0];
    }
  return (TYPE (c) == G_UNICODE_LOWERCASE_LETTER
	  ? ATTTABLE (c >> 8, c & 0xff)
	  : c);
}

/**
 * g_unichar_digit_value:
 * @c: a Unicode character
 *
 * Determines the numeric value of a character as a decimal
 * digit.
 *
 * Return value: If @c is a decimal digit (according to
 * g_unichar_isdigit()), its numeric value. Otherwise, -1.
 **/
int
g_unichar_digit_value (gunichar c)
{
  if (TYPE (c) == G_UNICODE_DECIMAL_NUMBER)
    return ATTTABLE (c >> 8, c & 0xff);
  return -1;
}

/**
 * g_unichar_xdigit_value:
 * @c: a Unicode character
 *
 * Determines the numeric value of a character as a hexidecimal
 * digit.
 *
 * Return value: If @c is a hex digit (according to
 * g_unichar_isxdigit()), its numeric value. Otherwise, -1.
 **/
int
g_unichar_xdigit_value (gunichar c)
{
  if (c >= 'A' && c <= 'F')
    return c - 'A' + 10;
  if (c >= 'a' && c <= 'f')
    return c - 'a' + 10;
  if (TYPE (c) == G_UNICODE_DECIMAL_NUMBER)
    return ATTTABLE (c >> 8, c & 0xff);
  return -1;
}

/**
 * g_unichar_type:
 * @c: a Unicode character
 * 
 * Classifies a Unicode character by type.
 * 
 * Return value: the type of the character.
 **/
GUnicodeType
g_unichar_type (gunichar c)
{
  return TYPE (c);
}

/*
 * Case mapping functions
 */

typedef enum {
  LOCALE_NORMAL,
  LOCALE_TURKIC,
  LOCALE_LITHUANIAN
} LocaleType;

static LocaleType
get_locale_type (void)
{
  const char *locale = setlocale (LC_CTYPE, NULL);

  switch (locale[0])
    {
   case 'a':
      if (locale[1] == 'z')
	return LOCALE_TURKIC;
      break;
    case 'l':
      if (locale[1] == 't')
	return LOCALE_LITHUANIAN;
      break;
    case 't':
      if (locale[1] == 'r')
	return LOCALE_TURKIC;
      break;
    }

  return LOCALE_NORMAL;
}

static int
output_marks (const char **p_inout,
	      char        *out_buffer,
	      int          len,
	      gboolean     remove_dot)
{
  const char *p = *p_inout;
  
  while (*p)
    {
      gunichar c = g_utf8_get_char (p);
      int t = TYPE(c);
      
      if (ISMARK(t))
	{
	  if (!remove_dot || c != 0x307 /* COMBINING DOT ABOVE */)
	    len += g_unichar_to_utf8 (c, out_buffer ? out_buffer + len : NULL);
	  p = g_utf8_next_char (p);
	}
      else
	break;
    }

  *p_inout = p;
  return len;
}

static gsize
output_special_case (gchar *out_buffer,
		     gsize  len,
		     int    index,
		     int    type,
		     int    which)
{
  const guchar *p = special_case_table[index];

  if (type != G_UNICODE_TITLECASE_LETTER)
    p += 2; /* +2 to skip over "best single match" */

  if (which == 1)
    {
      while (p[0] && p[1])
	p += 2;
      p += 2;
    }

  while (TRUE)
    {
      gunichar ch = p[0] * 256 + p[1];
      if (!ch)
	break;

      len += g_unichar_to_utf8 (ch, out_buffer ? out_buffer + len : NULL);
      p += 2;
    }

  return len;
}

static gsize
real_toupper (const gchar *str,
	      gssize       max_len,
	      gchar       *out_buffer,
	      LocaleType   locale_type)
{
  const gchar *p = str;
  const char *last = NULL;
  gsize len = 0;
  gboolean last_was_i = FALSE;

  while ((max_len < 0 || p < str + max_len) && *p)
    {
      gunichar c = g_utf8_get_char (p);
      int t = TYPE (c);
      gunichar val;

      last = p;
      p = g_utf8_next_char (p);

      if (locale_type == LOCALE_LITHUANIAN)
	{
	  if (c == 'i')
	    last_was_i = TRUE;
	  else 
	    {
	      if (last_was_i)
		{
		  /* Nasty, need to remove any dot above. Though
		   * I think only E WITH DOT ABOVE occurs in practice
		   * which could simplify this considerably.
		   */
		  gsize decomp_len, i;
		  gunichar *decomp;

		  decomp = g_unicode_canonical_decomposition (c, &decomp_len);
		  for (i=0; i < decomp_len; i++)
		    {
		      if (decomp[i] != 0x307 /* COMBINING DOT ABOVE */)
			len += g_unichar_to_utf8 (g_unichar_toupper (decomp[i]), out_buffer ? out_buffer + len : NULL);
		    }
		  g_free (decomp);
		  
		  len = output_marks (&p, out_buffer, len, TRUE);

		  continue;
		}

	      if (!ISMARK(t))
		last_was_i = FALSE;
	    }
	}
      
      if (locale_type == LOCALE_TURKIC && c == 'i')
	{
	  /* i => LATIN CAPITAL LETTER I WITH DOT ABOVE */
	  len += g_unichar_to_utf8 (0x130, out_buffer ? out_buffer + len : NULL); 
	}
      else if (c == 0x0345)	/* COMBINING GREEK YPOGEGRAMMENI */
	{
	  /* Nasty, need to move it after other combining marks .. this would go away if
	   * we normalized first.
	   */
	  len = output_marks (&p, out_buffer, len, FALSE);

	  /* And output as GREEK CAPITAL LETTER IOTA */
	  len += g_unichar_to_utf8 (0x399, out_buffer ? out_buffer + len : NULL); 	  
	}
      else if (t == G_UNICODE_LOWERCASE_LETTER || t == G_UNICODE_TITLECASE_LETTER)
	{
	  val = ATTTABLE (c >> 8, c & 0xff);

	  if (val >= 0xd800 && val < 0xdc00)
	    {
	      len += output_special_case (out_buffer, len, val - 0xd800, t,
					  t == G_UNICODE_LOWERCASE_LETTER ? 0 : 1);
	    }
	  else
	    {
	      if (t == G_UNICODE_TITLECASE_LETTER)
		{
		  unsigned int i;
		  for (i = 0; i < G_N_ELEMENTS (title_table); ++i)
		    {
		      if (title_table[i][0] == c)
			val = title_table[i][1];
		    }
		}

	      len += g_unichar_to_utf8 (val, out_buffer ? out_buffer + len : NULL);
	    }
	}
      else
	{
	  gsize char_len = g_utf8_skip[*(guchar *)last];

	  if (out_buffer)
	    memcpy (out_buffer + len, last, char_len);

	  len += char_len;
	}

    }

  return len;
}

/**
 * g_utf8_strup:
 * @str: a UTF-8 encoded string
 * @len: length of @str, in bytes, or -1 if @str is nul-terminated.
 * 
 * Converts all Unicode characters in the string that have a case
 * to uppercase. The exact manner that this is done depends
 * on the current locale, and may result in the number of
 * characters in the string increasing. (For instance, the
 * German ess-zet will be changed to SS.)
 * 
 * Return value: a newly allocated string, with all characters
 *    converted to uppercase.  
 **/
gchar *
g_utf8_strup (const gchar *str,
	      gssize       len)
{
  gsize result_len;
  LocaleType locale_type;
  gchar *result;

  g_return_val_if_fail (str != NULL, NULL);

  locale_type = get_locale_type ();
  
  /*
   * We use a two pass approach to keep memory management simple
   */
  result_len = real_toupper (str, len, NULL, locale_type);
  result = g_malloc (result_len + 1);
  real_toupper (str, len, result, locale_type);
  result[result_len] = '\0';

  return result;
}

static gsize
real_tolower (const gchar *str,
	      gssize       max_len,
	      gchar       *out_buffer,
	      LocaleType   locale_type)
{
  const gchar *p = str;
  const char *last = NULL;
  gsize len = 0;

  while ((max_len < 0 || p < str + max_len) && *p)
    {
      gunichar c = g_utf8_get_char (p);
      int t = TYPE (c);
      gunichar val;

      last = p;
      p = g_utf8_next_char (p);

      if (locale_type == LOCALE_TURKIC && c == 'I')
	{
	  /* I => LATIN SMALL LETTER DOTLESS I */
	  len += g_unichar_to_utf8 (0x131, out_buffer ? out_buffer + len : NULL); 
	}
      else if (c == 0x03A3)	/* GREEK CAPITAL LETTER SIGMA */
	{
	  gunichar next_c = g_utf8_get_char (p);
	  int next_t = TYPE(next_c);

	  /* SIGMA mapps differently depending on whether it is
	   * final or not. The following simplified test would
	   * fail in the case of combining marks following the
	   * sigma, but I don't think that occurs in real text.
	   * The test here matches that in ICU.
	   */
	  if (ISALPHA(next_t)) /* Lu,Ll,Lt,Lm,Lo */
	    val = 0x3c3;	/* GREEK SMALL SIGMA */
	  else
	    val = 0x3c2;	/* GREEK SMALL FINAL SIGMA */

	  len += g_unichar_to_utf8 (val, out_buffer ? out_buffer + len : NULL);
	}
      else if (t == G_UNICODE_UPPERCASE_LETTER || t == G_UNICODE_TITLECASE_LETTER)
	{
	  val = ATTTABLE (c >> 8, c & 0xff);

	  if (val >= 0xd800 && val < 0xdc00)
	    {
	      len += output_special_case (out_buffer, len, val - 0xd800, t, 0);
	    }
	  else
	    {
	      if (t == G_UNICODE_TITLECASE_LETTER)
		{
		  unsigned int i;
		  for (i = 0; i < G_N_ELEMENTS (title_table); ++i)
		    {
		      if (title_table[i][0] == c)
			val = title_table[i][2];
		    }
		}

	      len += g_unichar_to_utf8 (val, out_buffer ? out_buffer + len : NULL);
	    }
	}
      else
	{
	  gsize char_len = g_utf8_skip[*(guchar *)last];

	  if (out_buffer)
	    memcpy (out_buffer + len, last, char_len);

	  len += char_len;
	}

    }

  return len;
}

/**
 * g_utf8_strdown:
 * @str: a UTF-8 encoded string
 * @len: length of @str, in bytes, or -1 if @str is nul-terminated.
 * 
 * Converts all Unicode characters in the string that have a case
 * to lowercase. The exact manner that this is done depends
 * on the current locale, and may result in the number of
 * characters in the string changing.
 * 
 * Return value: a newly allocated string, with all characters
 *    converted to lowercase.  
 **/
gchar *
g_utf8_strdown (const gchar *str,
		gssize       len)
{
  gsize result_len;
  LocaleType locale_type;
  gchar *result;

  g_return_val_if_fail (str != NULL, NULL);

  locale_type = get_locale_type ();
  
  /*
   * We use a two pass approach to keep memory management simple
   */
  result_len = real_tolower (str, len, NULL, locale_type);
  result = g_malloc (result_len + 1);
  real_tolower (str, len, result, locale_type);
  result[result_len] = '\0';

  return result;
}

/**
 * g_utf8_casefold:
 * @str: a UTF-8 encoded string
 * @len: length of @str, in bytes, or -1 if @str is nul-terminated.
 * 
 * Converts a string into a form that is independent of case. The
 * result will not correspond to any particular case, but can be
 * compared for equality or ordered with the results of calling
 * g_utf8_casefold() on other strings.
 * 
 * Note that calling g_utf8_casefold() followed by g_utf8_collate() is
 * only an approximation to the correct linguistic case insensitive
 * ordering, though it is a fairly good one. Getting this exactly
 * right would require a more sophisticated collation function that
 * takes case sensitivity into account. GLib does not currently
 * provide such a function.
 * 
 * Return value: a newly allocated string, that is a
 *   case independent form of @str.
 **/
gchar *
g_utf8_casefold (const gchar *str,
		 gssize       len)
{
  GString *result = g_string_new (NULL);
  const char *p;

  p = str;
  while ((len < 0 || p < str + len) && *p)
    {
      gunichar ch = g_utf8_get_char (p);

      int start = 0;
      int end = G_N_ELEMENTS (casefold_table);

      if (ch >= casefold_table[start].ch &&
	  ch <= casefold_table[end - 1].ch)
	{
	  while (TRUE)
	    {
	      int half = (start + end) / 2;
	      if (ch == casefold_table[half].ch)
		{
		  g_string_append (result, casefold_table[half].data);
		  goto next;
		}
	      else if (half == start)
		break;
	      else if (ch > casefold_table[half].ch)
		start = half;
	      else
		end = half;
	    }
	}

      g_string_append_unichar (result, g_unichar_tolower (ch));
      
    next:
      p = g_utf8_next_char (p);
    }

  return g_string_free (result, FALSE); 
}