/*============================================================================
  CMake - Cross Platform Makefile Generator
  Copyright 2000-2009 Kitware, Inc., Insight Software Consortium

  Distributed under the OSI-approved BSD License (the "License");
  see accompanying file Copyright.txt for details.

  This software is distributed WITHOUT ANY WARRANTY; without even the
  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  See the License for more information.
============================================================================*/
#include "cm_utf8.h"

/*
  RFC 3629
  07-bit: 0xxxxxxx
  11-bit: 110xxxxx 10xxxxxx
  16-bit: 1110xxxx 10xxxxxx 10xxxxxx
  21-bit: 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

  Pre-RFC Compatibility
  26-bit: 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
  31-bit: 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx
*/

/* Number of leading ones before a zero in the byte.  */
static unsigned char const cm_utf8_ones[256] = {
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
  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,
  3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,6,6,7,8
};

/* Mask away control bits from bytes with n leading ones.  */
static unsigned char const cm_utf8_mask[7] = {
  0xEF, 0x3F, 0x1F, 0x0F, 0x07, 0x03, 0x01
};

/* Minimum allowed value when first byte has n leading ones.  */
static unsigned int const cm_utf8_min[7] = {
  0, 0, 1u<<7, 1u<<11, 1u<<16, 1u<<21, 1u<<26 /*, 1u<<31 */
};

/*--------------------------------------------------------------------------*/
const char* cm_utf8_decode_character(const char* first, const char* last,
                                     unsigned int* pc)
{
  /* Count leading ones in the first byte.  */
  unsigned char c = *first++;
  unsigned char const ones = cm_utf8_ones[c];
  switch(ones)
    {
    case 0: *pc = c; return first;    /* One-byte character.  */
    case 1: case 7: case 8: return 0; /* Invalid leading byte.  */
    default: break;
    }

  /* Extract bits from this multi-byte character.  */
  {
  unsigned int uc = c & cm_utf8_mask[ones];
  unsigned char left;
  for(left = ones-1; left && first != last; --left)
    {
    c = *first++;
    if(cm_utf8_ones[c] != 1)
      {
      return 0;
      }
    uc = (uc << 6) | (c & cm_utf8_mask[1]);
    }

  if(left > 0 || uc < cm_utf8_min[ones])
    {
    return 0;
    }

  *pc = uc;
  return first;
  }
}