/* nfkc.c	Unicode normalization utilities.
 * Copyright (C) 2002, 2003  Simon Josefsson
 *
 * This file is part of GNU Libidn.
 *
 * GNU Libidn 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 2.1 of the License, or (at your option) any later version.
 *
 * GNU Libidn 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 GNU Libidn; if not, see <http://www.gnu.org/licenses/>.
 */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <stdlib.h>
#include <string.h>
#include <stdint.h>

#include "stringprep.h"

/* This file contains functions from GLIB, including gutf8.c and
 * gunidecomp.c, all licensed under LGPL and copyright hold by:
 *
 *  Copyright (C) 1999, 2000 Tom Tromey
 *  Copyright 2000 Red Hat, Inc.
 */

/* Hacks to make syncing with GLIB code easier. */
#define gboolean int
#define gchar char
#define guchar unsigned char
#define glong long
#define gint int
#define guint unsigned int
#define gushort unsigned short
#define gint16 int16_t
#define guint16 uint16_t
#define gunichar uint32_t
#define gsize size_t
#define gssize ssize_t
#define g_malloc malloc
#define g_free free
#define GError void
#define g_set_error(a,b,c,d) ((void) 0)
#define g_new(struct_type, n_structs)					\
  ((struct_type *) g_malloc (((gsize) sizeof (struct_type)) * ((gsize) (n_structs))))
#  if defined (__GNUC__) && !defined (__STRICT_ANSI__) && !defined (__cplusplus)
#    define G_STMT_START	(void)(
#    define G_STMT_END		)
#  else
#    if (defined (sun) || defined (__sun__))
#      define G_STMT_START	if (1)
#      define G_STMT_END	else (void)0
#    else
#      define G_STMT_START	do
#      define G_STMT_END	while (0)
#    endif
#  endif
#define g_return_val_if_fail(expr,val)		G_STMT_START{ (void)0; }G_STMT_END
#define G_N_ELEMENTS(arr)		(sizeof (arr) / sizeof ((arr)[0]))
#define TRUE 1
#define FALSE 0

/* Code from GLIB gunicode.h starts here. */

typedef enum
{
  G_NORMALIZE_DEFAULT,
  G_NORMALIZE_NFD = G_NORMALIZE_DEFAULT,
  G_NORMALIZE_DEFAULT_COMPOSE,
  G_NORMALIZE_NFC = G_NORMALIZE_DEFAULT_COMPOSE,
  G_NORMALIZE_ALL,
  G_NORMALIZE_NFKD = G_NORMALIZE_ALL,
  G_NORMALIZE_ALL_COMPOSE,
  G_NORMALIZE_NFKC = G_NORMALIZE_ALL_COMPOSE
}
GNormalizeMode;

/* Code from GLIB gutf8.c starts here. */

#define UTF8_COMPUTE(Char, Mask, Len)		\
  if (Char < 128)				\
    {						\
      Len = 1;					\
      Mask = 0x7f;				\
    }						\
  else if ((Char & 0xe0) == 0xc0)		\
    {						\
      Len = 2;					\
      Mask = 0x1f;				\
    }						\
  else if ((Char & 0xf0) == 0xe0)		\
    {						\
      Len = 3;					\
      Mask = 0x0f;				\
    }						\
  else if ((Char & 0xf8) == 0xf0)		\
    {						\
      Len = 4;					\
      Mask = 0x07;				\
    }						\
  else if ((Char & 0xfc) == 0xf8)		\
    {						\
      Len = 5;					\
      Mask = 0x03;				\
    }						\
  else if ((Char & 0xfe) == 0xfc)		\
    {						\
      Len = 6;					\
      Mask = 0x01;				\
    }						\
  else						\
    Len = -1;

#define UTF8_LENGTH(Char)			\
  ((Char) < 0x80 ? 1 :				\
   ((Char) < 0x800 ? 2 :			\
    ((Char) < 0x10000 ? 3 :			\
     ((Char) < 0x200000 ? 4 :			\
      ((Char) < 0x4000000 ? 5 : 6)))))


#define UTF8_GET(Result, Chars, Count, Mask, Len)	\
  (Result) = (Chars)[0] & (Mask);			\
  for ((Count) = 1; (Count) < (Len); ++(Count))		\
    {							\
      if (((Chars)[(Count)] & 0xc0) != 0x80)		\
	{						\
	  (Result) = -1;				\
	  break;					\
	}						\
      (Result) <<= 6;					\
      (Result) |= ((Chars)[(Count)] & 0x3f);		\
    }

#define UNICODE_VALID(Char)			\
  ((Char) < 0x110000 &&				\
   (((Char) & 0xFFFFF800) != 0xD800) &&		\
   ((Char) < 0xFDD0 || (Char) > 0xFDEF) &&	\
   ((Char) & 0xFFFE) != 0xFFFE)


static const gchar utf8_skip_data[256] = {
  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,
  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,
  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,
  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,
  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,
  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, 2, 2, 2, 2, 2, 2, 2, 2, 2,
  2, 2, 2, 2, 2, 2, 2,
  3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 5,
  5, 5, 5, 6, 6, 1, 1
};

const gchar *const g_utf8_skip = utf8_skip_data;

#define g_utf8_next_char(p) (char *)((p) + g_utf8_skip[*(guchar *)(p)])

/*
 * g_utf8_strlen:
 * @p: pointer to the start of a UTF-8 encoded string.
 * @max: the maximum number of bytes to examine. If @max
 *       is less than 0, then the string is assumed to be
 *       nul-terminated. If @max is 0, @p will not be examined and
 *       may be %NULL.
 *
 * Returns the length of the string in characters.
 *
 * Return value: the length of the string in characters
 **/
static glong
g_utf8_strlen (const gchar * p, gssize max)
{
  glong len = 0;
  const gchar *start = p;
  g_return_val_if_fail (p != NULL || max == 0, 0);

  if (max < 0)
    {
      while (*p)
	{
	  p = g_utf8_next_char (p);
	  ++len;
	}
    }
  else
    {
      if (max == 0 || !*p)
	return 0;

      p = g_utf8_next_char (p);

      while (p - start < max && *p)
	{
	  ++len;
	  p = g_utf8_next_char (p);
	}

      /* only do the last len increment if we got a complete
       * char (don't count partial chars)
       */
      if (p - start == max)
	++len;
    }

  return len;
}

/*
 * g_utf8_get_char:
 * @p: a pointer to Unicode character encoded as UTF-8
 *
 * Converts a sequence of bytes encoded as UTF-8 to a Unicode character.
 * If @p does not point to a valid UTF-8 encoded character, results are
 * undefined. If you are not sure that the bytes are complete
 * valid Unicode characters, you should use g_utf8_get_char_validated()
 * instead.
 *
 * Return value: the resulting character
 **/
static gunichar
g_utf8_get_char (const gchar * p)
{
  int i, mask = 0, len;
  gunichar result;
  unsigned char c = (unsigned char) *p;

  UTF8_COMPUTE (c, mask, len);
  if (len == -1)
    return (gunichar) - 1;
  UTF8_GET (result, p, i, mask, len);

  return result;
}

/*
 * g_unichar_to_utf8:
 * @c: a ISO10646 character code
 * @outbuf: output buffer, must have at least 6 bytes of space.
 *       If %NULL, the length will be computed and returned
 *       and nothing will be written to @outbuf.
 *
 * Converts a single character to UTF-8.
 *
 * Return value: number of bytes written
 **/
static int
g_unichar_to_utf8 (gunichar c, gchar * outbuf)
{
  guint len = 0;
  int first;
  int i;

  if (c < 0x80)
    {
      first = 0;
      len = 1;
    }
  else if (c < 0x800)
    {
      first = 0xc0;
      len = 2;
    }
  else if (c < 0x10000)
    {
      first = 0xe0;
      len = 3;
    }
  else if (c < 0x200000)
    {
      first = 0xf0;
      len = 4;
    }
  else if (c < 0x4000000)
    {
      first = 0xf8;
      len = 5;
    }
  else
    {
      first = 0xfc;
      len = 6;
    }

  if (outbuf)
    {
      for (i = len - 1; i > 0; --i)
	{
	  outbuf[i] = (c & 0x3f) | 0x80;
	  c >>= 6;
	}
      outbuf[0] = c | first;
    }

  return len;
}

/*
 * g_utf8_to_ucs4_fast:
 * @str: a UTF-8 encoded string
 * @len: the maximum length of @str to use. If @len < 0, then
 *       the string is nul-terminated.
 * @items_written: location to store the number of characters in the
 *                 result, or %NULL.
 *
 * Convert a string from UTF-8 to a 32-bit fixed width
 * representation as UCS-4, assuming valid UTF-8 input.
 * This function is roughly twice as fast as g_utf8_to_ucs4()
 * but does no error checking on the input.
 *
 * Return value: a pointer to a newly allocated UCS-4 string.
 *               This value must be freed with g_free().
 **/
static gunichar *
g_utf8_to_ucs4_fast (const gchar * str, glong len, glong * items_written)
{
  gint j, charlen;
  gunichar *result;
  gint n_chars, i;
  const gchar *p;

  g_return_val_if_fail (str != NULL, NULL);

  p = str;
  n_chars = 0;
  if (len < 0)
    {
      while (*p)
	{
	  p = g_utf8_next_char (p);
	  ++n_chars;
	}
    }
  else
    {
      while (p < str + len && *p)
	{
	  p = g_utf8_next_char (p);
	  ++n_chars;
	}
    }

  result = g_new (gunichar, n_chars + 1);
  if (!result)
    return NULL;

  p = str;
  for (i = 0; i < n_chars; i++)
    {
      gunichar wc = ((unsigned char *) p)[0];

      if (wc < 0x80)
	{
	  result[i] = wc;
	  p++;
	}
      else
	{
	  if (wc < 0xe0)
	    {
	      charlen = 2;
	      wc &= 0x1f;
	    }
	  else if (wc < 0xf0)
	    {
	      charlen = 3;
	      wc &= 0x0f;
	    }
	  else if (wc < 0xf8)
	    {
	      charlen = 4;
	      wc &= 0x07;
	    }
	  else if (wc < 0xfc)
	    {
	      charlen = 5;
	      wc &= 0x03;
	    }
	  else
	    {
	      charlen = 6;
	      wc &= 0x01;
	    }

	  for (j = 1; j < charlen; j++)
	    {
	      wc <<= 6;
	      wc |= ((unsigned char *) p)[j] & 0x3f;
	    }

	  result[i] = wc;
	  p += charlen;
	}
    }
  result[i] = 0;

  if (items_written)
    *items_written = i;

  return result;
}

/*
 * g_ucs4_to_utf8:
 * @str: a UCS-4 encoded string
 * @len: the maximum length of @str to use. If @len < 0, then
 *       the string is terminated with a 0 character.
 * @items_read: location to store number of characters read read, or %NULL.
 * @items_written: location to store number of bytes written or %NULL.
 *                 The value here stored does not include the trailing 0
 *                 byte.
 * @error: location to store the error occuring, or %NULL to ignore
 *         errors. Any of the errors in #GConvertError other than
 *         %G_CONVERT_ERROR_NO_CONVERSION may occur.
 *
 * Convert a string from a 32-bit fixed width representation as UCS-4.
 * to UTF-8. The result will be terminated with a 0 byte.
 *
 * Return value: a pointer to a newly allocated UTF-8 string.
 *               This value must be freed with g_free(). If an
 *               error occurs, %NULL will be returned and
 *               @error set.
 **/
static gchar *
g_ucs4_to_utf8 (const gunichar * str,
		glong len,
		glong * items_read, glong * items_written, GError ** error)
{
  gint result_length;
  gchar *result = NULL;
  gchar *p;
  gint i;

  result_length = 0;
  for (i = 0; len < 0 || i < len; i++)
    {
      if (!str[i])
	break;

      if (str[i] >= 0x80000000)
	{
	  if (items_read)
	    *items_read = i;

	  g_set_error (error, G_CONVERT_ERROR,
		       G_CONVERT_ERROR_ILLEGAL_SEQUENCE,
		       _("Character out of range for UTF-8"));
	  goto err_out;
	}

      result_length += UTF8_LENGTH (str[i]);
    }

  result = g_malloc (result_length + 1);
  if (!result)
    return NULL;
  p = result;

  i = 0;
  while (p < result + result_length)
    p += g_unichar_to_utf8 (str[i++], p);

  *p = '\0';

  if (items_written)
    *items_written = p - result;

err_out:
  if (items_read)
    *items_read = i;

  return result;
}

/* Code from GLIB gunidecomp.c starts here. */

#include "gunidecomp.h"
#include "gunicomp.h"

#define CC_PART1(Page, Char) \
  ((combining_class_table_part1[Page] >= G_UNICODE_MAX_TABLE_INDEX) \
   ? (combining_class_table_part1[Page] - G_UNICODE_MAX_TABLE_INDEX) \
   : (cclass_data[combining_class_table_part1[Page]][Char]))

#define CC_PART2(Page, Char) \
  ((combining_class_table_part2[Page] >= G_UNICODE_MAX_TABLE_INDEX) \
   ? (combining_class_table_part2[Page] - G_UNICODE_MAX_TABLE_INDEX) \
   : (cclass_data[combining_class_table_part2[Page]][Char]))

#define COMBINING_CLASS(Char) \
  (((Char) <= G_UNICODE_LAST_CHAR_PART1) \
   ? CC_PART1 ((Char) >> 8, (Char) & 0xff) \
   : (((Char) >= 0xe0000 && (Char) <= G_UNICODE_LAST_CHAR) \
      ? CC_PART2 (((Char) - 0xe0000) >> 8, (Char) & 0xff) \
      : 0))

/* constants for hangul syllable [de]composition */
#define SBase 0xAC00
#define LBase 0x1100
#define VBase 0x1161
#define TBase 0x11A7
#define LCount 19
#define VCount 21
#define TCount 28
#define NCount (VCount * TCount)
#define SCount (LCount * NCount)

/*
 * g_unicode_canonical_ordering:
 * @string: a UCS-4 encoded string.
 * @len: the maximum length of @string to use.
 *
 * Computes the canonical ordering of a string in-place.
 * This rearranges decomposed characters in the string
 * according to their combining classes.  See the Unicode
 * manual for more information.
 **/
static void
g_unicode_canonical_ordering (gunichar * string, gsize len)
{
  gsize i;
  int swap = 1;

  while (swap)
    {
      int last;
      swap = 0;
      last = COMBINING_CLASS (string[0]);
      for (i = 0; i < len - 1; ++i)
	{
	  int next = COMBINING_CLASS (string[i + 1]);
	  if (next != 0 && last > next)
	    {
	      gsize j;
	      /* Percolate item leftward through string.  */
	      for (j = i + 1; j > 0; --j)
		{
		  gunichar t;
		  if (COMBINING_CLASS (string[j - 1]) <= next)
		    break;
		  t = string[j];
		  string[j] = string[j - 1];
		  string[j - 1] = t;
		  swap = 1;
		}
	      /* We're re-entering the loop looking at the old
	         character again.  */
	      next = last;
	    }
	  last = next;
	}
    }
}

/* http://www.unicode.org/unicode/reports/tr15/#Hangul
 * r should be null or have sufficient space. Calling with r == NULL will
 * only calculate the result_len; however, a buffer with space for three
 * characters will always be big enough. */
static void
decompose_hangul (gunichar s, gunichar * r, gsize * result_len)
{
  gint SIndex = s - SBase;

  /* not a hangul syllable */
  if (SIndex < 0 || SIndex >= SCount)
    {
      if (r)
	r[0] = s;
      *result_len = 1;
    }
  else
    {
      gunichar L = LBase + SIndex / NCount;
      gunichar V = VBase + (SIndex % NCount) / TCount;
      gunichar T = TBase + SIndex % TCount;

      if (r)
	{
	  r[0] = L;
	  r[1] = V;
	}

      if (T != TBase)
	{
	  if (r)
	    r[2] = T;
	  *result_len = 3;
	}
      else
	*result_len = 2;
    }
}

/* returns a pointer to a null-terminated UTF-8 string */
static const gchar *
find_decomposition (gunichar ch, gboolean compat)
{
  int start = 0;
  int end = G_N_ELEMENTS (decomp_table);

  if (ch >= decomp_table[start].ch && ch <= decomp_table[end - 1].ch)
    {
      while (TRUE)
	{
	  int half = (start + end) / 2;
	  if (ch == decomp_table[half].ch)
	    {
	      int offset;

	      if (compat)
		{
		  offset = decomp_table[half].compat_offset;
		  if (offset == G_UNICODE_NOT_PRESENT_OFFSET)
		    offset = decomp_table[half].canon_offset;
		}
	      else
		{
		  offset = decomp_table[half].canon_offset;
		  if (offset == G_UNICODE_NOT_PRESENT_OFFSET)
		    return NULL;
		}

	      return &(decomp_expansion_string[offset]);
	    }
	  else if (half == start)
	    break;
	  else if (ch > decomp_table[half].ch)
	    start = half;
	  else
	    end = half;
	}
    }

  return NULL;
}

/* L,V => LV and LV,T => LVT  */
static gboolean
combine_hangul (gunichar a, gunichar b, gunichar * result)
{
  gint LIndex = a - LBase;
  gint SIndex = a - SBase;

  gint VIndex = b - VBase;
  gint TIndex = b - TBase;

  if (0 <= LIndex && LIndex < LCount && 0 <= VIndex && VIndex < VCount)
    {
      *result = SBase + (LIndex * VCount + VIndex) * TCount;
      return TRUE;
    }
  else if (0 <= SIndex && SIndex < SCount && (SIndex % TCount) == 0
	   && 0 <= TIndex && TIndex <= TCount)
    {
      *result = a + TIndex;
      return TRUE;
    }

  return FALSE;
}

#define CI(Page, Char) \
  ((compose_table[Page] >= G_UNICODE_MAX_TABLE_INDEX) \
   ? (compose_table[Page] - G_UNICODE_MAX_TABLE_INDEX) \
   : (compose_data[compose_table[Page]][Char]))

#define COMPOSE_INDEX(Char) \
     ((((Char) >> 8) > (COMPOSE_TABLE_LAST)) ? 0 : CI((Char) >> 8, (Char) & 0xff))

static gboolean
combine (gunichar a, gunichar b, gunichar * result)
{
  gushort index_a, index_b;

  if (combine_hangul (a, b, result))
    return TRUE;

  index_a = COMPOSE_INDEX (a);

  if (index_a >= COMPOSE_FIRST_SINGLE_START && index_a < COMPOSE_SECOND_START)
    {
      if (b == compose_first_single[index_a - COMPOSE_FIRST_SINGLE_START][0])
	{
	  *result =
	    compose_first_single[index_a - COMPOSE_FIRST_SINGLE_START][1];
	  return TRUE;
	}
      else
	return FALSE;
    }

  index_b = COMPOSE_INDEX (b);

  if (index_b >= COMPOSE_SECOND_SINGLE_START)
    {
      if (a ==
	  compose_second_single[index_b - COMPOSE_SECOND_SINGLE_START][0])
	{
	  *result =
	    compose_second_single[index_b - COMPOSE_SECOND_SINGLE_START][1];
	  return TRUE;
	}
      else
	return FALSE;
    }

  if (index_a >= COMPOSE_FIRST_START && index_a < COMPOSE_FIRST_SINGLE_START
      && index_b >= COMPOSE_SECOND_START
      && index_b < COMPOSE_SECOND_SINGLE_START)
    {
      gunichar res =
	compose_array[index_a - COMPOSE_FIRST_START][index_b -
						     COMPOSE_SECOND_START];

      if (res)
	{
	  *result = res;
	  return TRUE;
	}
    }

  return FALSE;
}

static gunichar *
_g_utf8_normalize_wc (const gchar * str, gssize max_len, GNormalizeMode mode)
{
  gsize n_wc;
  gunichar *wc_buffer;
  const char *p;
  gsize last_start;
  gboolean do_compat = (mode == G_NORMALIZE_NFKC || mode == G_NORMALIZE_NFKD);
  gboolean do_compose = (mode == G_NORMALIZE_NFC || mode == G_NORMALIZE_NFKC);

  n_wc = 0;
  p = str;
  while ((max_len < 0 || p < str + max_len) && *p)
    {
      const gchar *decomp;
      gunichar wc = g_utf8_get_char (p);

      if (wc >= 0xac00 && wc <= 0xd7af)
	{
	  gsize result_len;
	  decompose_hangul (wc, NULL, &result_len);
	  n_wc += result_len;
	}
      else
	{
	  decomp = find_decomposition (wc, do_compat);

	  if (decomp)
	    n_wc += g_utf8_strlen (decomp, -1);
	  else
	    n_wc++;
	}

      p = g_utf8_next_char (p);
    }

  wc_buffer = g_new (gunichar, n_wc + 1);
  if (!wc_buffer)
    return NULL;

  last_start = 0;
  n_wc = 0;
  p = str;
  while ((max_len < 0 || p < str + max_len) && *p)
    {
      gunichar wc = g_utf8_get_char (p);
      const gchar *decomp;
      int cc;
      gsize old_n_wc = n_wc;

      if (wc >= 0xac00 && wc <= 0xd7af)
	{
	  gsize result_len;
	  decompose_hangul (wc, wc_buffer + n_wc, &result_len);
	  n_wc += result_len;
	}
      else
	{
	  decomp = find_decomposition (wc, do_compat);

	  if (decomp)
	    {
	      const char *pd;
	      for (pd = decomp; *pd != '\0'; pd = g_utf8_next_char (pd))
		wc_buffer[n_wc++] = g_utf8_get_char (pd);
	    }
	  else
	    wc_buffer[n_wc++] = wc;
	}

      if (n_wc > 0)
	{
	  cc = COMBINING_CLASS (wc_buffer[old_n_wc]);

	  if (cc == 0)
	    {
	      g_unicode_canonical_ordering (wc_buffer + last_start,
					    n_wc - last_start);
	      last_start = old_n_wc;
	    }
	}

      p = g_utf8_next_char (p);
    }

  if (n_wc > 0)
    {
      g_unicode_canonical_ordering (wc_buffer + last_start,
				    n_wc - last_start);
      last_start = n_wc;
    }

  wc_buffer[n_wc] = 0;

  /* All decomposed and reordered */

  if (do_compose && n_wc > 0)
    {
      gsize i, j;
      int last_cc = 0;
      last_start = 0;

      for (i = 0; i < n_wc; i++)
	{
	  int cc = COMBINING_CLASS (wc_buffer[i]);

	  if (i > 0 &&
	      (last_cc == 0 || last_cc != cc) &&
	      combine (wc_buffer[last_start], wc_buffer[i],
		       &wc_buffer[last_start]))
	    {
	      for (j = i + 1; j < n_wc; j++)
		wc_buffer[j - 1] = wc_buffer[j];
	      n_wc--;
	      i--;

	      if (i == last_start)
		last_cc = 0;
	      else
		last_cc = COMBINING_CLASS (wc_buffer[i - 1]);

	      continue;
	    }

	  if (cc == 0)
	    last_start = i;

	  last_cc = cc;
	}
    }

  wc_buffer[n_wc] = 0;

  return wc_buffer;
}

/*
 * g_utf8_normalize:
 * @str: a UTF-8 encoded string.
 * @len: length of @str, in bytes, or -1 if @str is nul-terminated.
 * @mode: the type of normalization to perform.
 *
 * Converts a string into canonical form, standardizing
 * such issues as whether a character with an accent
 * is represented as a base character and combining
 * accent or as a single precomposed character. You
 * should generally call g_utf8_normalize() before
 * comparing two Unicode strings.
 *
 * The normalization mode %G_NORMALIZE_DEFAULT only
 * standardizes differences that do not affect the
 * text content, such as the above-mentioned accent
 * representation. %G_NORMALIZE_ALL also standardizes
 * the "compatibility" characters in Unicode, such
 * as SUPERSCRIPT THREE to the standard forms
 * (in this case DIGIT THREE). Formatting information
 * may be lost but for most text operations such
 * characters should be considered the same.
 * For example, g_utf8_collate() normalizes
 * with %G_NORMALIZE_ALL as its first step.
 *
 * %G_NORMALIZE_DEFAULT_COMPOSE and %G_NORMALIZE_ALL_COMPOSE
 * are like %G_NORMALIZE_DEFAULT and %G_NORMALIZE_ALL,
 * but returned a result with composed forms rather
 * than a maximally decomposed form. This is often
 * useful if you intend to convert the string to
 * a legacy encoding or pass it to a system with
 * less capable Unicode handling.
 *
 * Return value: a newly allocated string, that is the
 *   normalized form of @str.
 **/
static gchar *
g_utf8_normalize (const gchar * str, gssize len, GNormalizeMode mode)
{
  gunichar *result_wc = _g_utf8_normalize_wc (str, len, mode);
  gchar *result;

  result = g_ucs4_to_utf8 (result_wc, -1, NULL, NULL, NULL);
  g_free (result_wc);

  return result;
}

/* Public Libidn API starts here. */

/**
 * stringprep_utf8_to_unichar:
 * @p: a pointer to Unicode character encoded as UTF-8
 *
 * Converts a sequence of bytes encoded as UTF-8 to a Unicode character.
 * If @p does not point to a valid UTF-8 encoded character, results are
 * undefined.
 *
 * Return value: the resulting character.
 **/
uint32_t
stringprep_utf8_to_unichar (const char *p)
{
  return g_utf8_get_char (p);
}

/**
 * stringprep_unichar_to_utf8:
 * @c: a ISO10646 character code
 * @outbuf: output buffer, must have at least 6 bytes of space.
 *       If %NULL, the length will be computed and returned
 *       and nothing will be written to @outbuf.
 *
 * Converts a single character to UTF-8.
 *
 * Return value: number of bytes written.
 **/
int
stringprep_unichar_to_utf8 (uint32_t c, char *outbuf)
{
  return g_unichar_to_utf8 (c, outbuf);
}

/**
 * stringprep_utf8_to_ucs4:
 * @str: a UTF-8 encoded string
 * @len: the maximum length of @str to use. If @len < 0, then
 *       the string is nul-terminated.
 * @items_written: location to store the number of characters in the
 *                 result, or %NULL.
 *
 * Convert a string from UTF-8 to a 32-bit fixed width
 * representation as UCS-4, assuming valid UTF-8 input.
 * This function does no error checking on the input.
 *
 * Return value: a pointer to a newly allocated UCS-4 string.
 *               This value must be freed with free().
 **/
uint32_t *
stringprep_utf8_to_ucs4 (const char *str, ssize_t len, size_t * items_written)
{
  return g_utf8_to_ucs4_fast (str, (glong) len, (glong *) items_written);
}

/**
 * stringprep_ucs4_to_utf8:
 * @str: a UCS-4 encoded string
 * @len: the maximum length of @str to use. If @len < 0, then
 *       the string is terminated with a 0 character.
 * @items_read: location to store number of characters read read, or %NULL.
 * @items_written: location to store number of bytes written or %NULL.
 *                 The value here stored does not include the trailing 0
 *                 byte.
 *
 * Convert a string from a 32-bit fixed width representation as UCS-4.
 * to UTF-8. The result will be terminated with a 0 byte.
 *
 * Return value: a pointer to a newly allocated UTF-8 string.
 *               This value must be freed with free(). If an
 *               error occurs, %NULL will be returned and
 *               @error set.
 **/
char *
stringprep_ucs4_to_utf8 (const uint32_t * str, ssize_t len,
			 size_t * items_read, size_t * items_written)
{
  return g_ucs4_to_utf8 (str, len, (glong *) items_read,
			 (glong *) items_written, NULL);
}

/**
 * stringprep_utf8_nfkc_normalize:
 * @str: a UTF-8 encoded string.
 * @len: length of @str, in bytes, or -1 if @str is nul-terminated.
 *
 * Converts a string into canonical form, standardizing
 * such issues as whether a character with an accent
 * is represented as a base character and combining
 * accent or as a single precomposed character.
 *
 * The normalization mode is NFKC (ALL COMPOSE).  It standardizes
 * differences that do not affect the text content, such as the
 * above-mentioned accent representation. It standardizes the
 * "compatibility" characters in Unicode, such as SUPERSCRIPT THREE to
 * the standard forms (in this case DIGIT THREE). Formatting
 * information may be lost but for most text operations such
 * characters should be considered the same. It returns a result with
 * composed forms rather than a maximally decomposed form.
 *
 * Return value: a newly allocated string, that is the
 *   NFKC normalized form of @str.
 **/
char *
stringprep_utf8_nfkc_normalize (const char *str, ssize_t len)
{
  return g_utf8_normalize (str, len, G_NORMALIZE_NFKC);
}

/**
 * stringprep_ucs4_nfkc_normalize:
 * @str: a Unicode string.
 * @len: length of @str array, or -1 if @str is nul-terminated.
 *
 * Converts UCS4 string into UTF-8 and runs
 * stringprep_utf8_nfkc_normalize().
 *
 * Return value: a newly allocated Unicode string, that is the NFKC
 *   normalized form of @str.
 **/
uint32_t *
stringprep_ucs4_nfkc_normalize (uint32_t * str, ssize_t len)
{
  char *p;
  uint32_t *result_wc;

  p = stringprep_ucs4_to_utf8 (str, len, 0, 0);
  result_wc = _g_utf8_normalize_wc (p, -1, G_NORMALIZE_NFKC);
  free (p);

  return result_wc;
}