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/* go-rune.c -- rune functions for Go.

   Copyright 2009, 2010 The Go Authors. All rights reserved.

   Use of this source code is governed by a BSD-style

   license that can be found in the LICENSE file.  */

#include <stddef.h>

#include "go-string.h"

/* Get a character from the UTF-8 string STR, of length LEN.  Store

   the Unicode character, if any, in *RUNE.  Return the number of

   characters used from STR.  */

int

__go_get_rune (const unsigned char *str, size_t len, int *rune)

{

  int c, c1, c2, c3;

  /* Default to the "replacement character".  */

  *rune = 0xfffd;

  if (len <= 0)

    return 1;

  c = *str;

  if (c <= 0x7f)

    {

      *rune = c;

      return 1;

    }

  if (len <= 1)

    return 1;

  c1 = str[1];

  if ((c & 0xe0) == 0xc0

      && (c1 & 0xc0) == 0x80)

    {

      *rune = (((c & 0x1f) << 6)

               + (c1 & 0x3f));

      return 2;

    }

  if (len <= 2)

    return 1;

  c2 = str[2];

  if ((c & 0xf0) == 0xe0

      && (c1 & 0xc0) == 0x80

      && (c2 & 0xc0) == 0x80)

    {

      *rune = (((c & 0xf) << 12)

               + ((c1 & 0x3f) << 6)

               + (c2 & 0x3f));

      return 3;

    }

  if (len <= 3)

    return 1;

  c3 = str[3];

  if ((c & 0xf8) == 0xf0

      && (c1 & 0xc0) == 0x80

      && (c2 & 0xc0) == 0x80

      && (c3 & 0xc0) == 0x80)

    {

      *rune = (((c & 0x7) << 18)

               + ((c1 & 0x3f) << 12)

               + ((c2 & 0x3f) << 6)

               + (c3 & 0x3f));

      return 4;

    }

  /* Invalid encoding.  Return 1 so that we advance.  */

  return 1;

}