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         (void)png_icc_profile_error(png_ptr, NULL, name, temp,
            "unexpected NamedColor ICC profile class");
         break;

      default:
         /* To allow for future enhancements to the profile accept unrecognized
          * profile classes with a warning, these then hit the test below on the
          * tag content to ensure they are backward compatible with one of the
          * understood profiles.
          */
         (void)png_icc_profile_error(png_ptr, NULL, name, temp,
            "unrecognized ICC profile class");
         break;
   }

   /* For any profile other than a device link one the PCS must be encoded
    * either in XYZ or Lab.
    */
   temp = png_get_uint_32(profile+20);
   switch (temp)
   {
      case 0x58595A20: /* 'XYZ ' */
      case 0x4C616220: /* 'Lab ' */
         break;

      default:
         return png_icc_profile_error(png_ptr, colorspace, name, temp,
            "unexpected ICC PCS encoding");
   }

   return 1;
}

int /* PRIVATE */
png_icc_check_tag_table(png_const_structrp png_ptr, png_colorspacerp colorspace,
   png_const_charp name, png_uint_32 profile_length,
   png_const_bytep profile /* header plus whole tag table */)
{
   png_uint_32 tag_count = png_get_uint_32(profile+128);
   png_uint_32 itag;
   png_const_bytep tag = profile+132; /* The first tag */

   /* First scan all the tags in the table and add bits to the icc_info value
    * (temporarily in 'tags').
    */
   for (itag=0; itag < tag_count; ++itag, tag += 12)
   {
      png_uint_32 tag_id = png_get_uint_32(tag+0);
      png_uint_32 tag_start = png_get_uint_32(tag+4); /* must be aligned */
      png_uint_32 tag_length = png_get_uint_32(tag+8);/* not padded */

      /* The ICC specification does not exclude zero length tags, therefore the
       * start might actually be anywhere if there is no data, but this would be
       * a clear abuse of the intent of the standard so the start is checked for
       * being in range.  All defined tag types have an 8 byte header - a 4 byte
       * type signature then 0.
       */
      if ((tag_start & 3) != 0)
      {
         /* CNHP730S.icc shipped with Microsoft Windows 64 violates this, it is
          * only a warning here because libpng does not care about the
          * alignment.
          */
         (void)png_icc_profile_error(png_ptr, NULL, name, tag_id,
            "ICC profile tag start not a multiple of 4");
      }

      /* This is a hard error; potentially it can cause read outside the
       * profile.
       */
      if (tag_start > profile_length || tag_length > profile_length - tag_start)
         return png_icc_profile_error(png_ptr, colorspace, name, tag_id,
            "ICC profile tag outside profile");
   }

   return 1; /* success, maybe with warnings */
}

#if defined(PNG_sRGB_SUPPORTED) && PNG_sRGB_PROFILE_CHECKS >= 0
/* Information about the known ICC sRGB profiles */
static const struct
{
   png_uint_32 adler, crc, length;
   png_uint_32 md5[4];
   png_byte    have_md5;
   png_byte    is_broken;
   png_uint_16 intent;

#  define PNG_MD5(a,b,c,d) { a, b, c, d }, (a!=0)||(b!=0)||(c!=0)||(d!=0)
#  define PNG_ICC_CHECKSUM(adler, crc, md5, intent, broke, date, length, fname)\
      { adler, crc, length, md5, broke, intent },

} png_sRGB_checks[] =
{
   /* This data comes from contrib/tools/checksum-icc run on downloads of
    * all four ICC sRGB profiles from www.color.org.
    */
   /* adler32, crc32, MD5[4], intent, date, length, file-name */
   PNG_ICC_CHECKSUM(0x0a3fd9f6, 0x3b8772b9,
      PNG_MD5(0x29f83dde, 0xaff255ae, 0x7842fae4, 0xca83390d), 0, 0,
      "2009/03/27 21:36:31", 3048, "sRGB_IEC61966-2-1_black_scaled.icc")

   /* ICC sRGB v2 perceptual no black-compensation: */
   PNG_ICC_CHECKSUM(0x4909e5e1, 0x427ebb21,
      PNG_MD5(0xc95bd637, 0xe95d8a3b, 0x0df38f99, 0xc1320389), 1, 0,
      "2009/03/27 21:37:45", 3052, "sRGB_IEC61966-2-1_no_black_scaling.icc")

   PNG_ICC_CHECKSUM(0xfd2144a1, 0x306fd8ae,
      PNG_MD5(0xfc663378, 0x37e2886b, 0xfd72e983, 0x8228f1b8), 0, 0,
      "2009/08/10 17:28:01", 60988, "sRGB_v4_ICC_preference_displayclass.icc")

   /* ICC sRGB v4 perceptual */
   PNG_ICC_CHECKSUM(0x209c35d2, 0xbbef7812,
      PNG_MD5(0x34562abf, 0x994ccd06, 0x6d2c5721, 0xd0d68c5d), 0, 0,
      "2007/07/25 00:05:37", 60960, "sRGB_v4_ICC_preference.icc")

   /* The following profiles have no known MD5 checksum. If there is a match
    * on the (empty) MD5 the other fields are used to attempt a match and
    * a warning is produced.  The first two of these profiles have a 'cprt' tag
    * which suggests that they were also made by Hewlett Packard.
    */