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   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.
    */
   PNG_ICC_CHECKSUM(0xa054d762, 0x5d5129ce,
      PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 1, 0,
      "2004/07/21 18:57:42", 3024, "sRGB_IEC61966-2-1_noBPC.icc")

   /* This is a 'mntr' (display) profile with a mediaWhitePointTag that does not
    * match the D50 PCS illuminant in the header (it is in fact the D65 values,
    * so the white point is recorded as the un-adapted value.)  The profiles
    * below only differ in one byte - the intent - and are basically the same as
    * the previous profile except for the mediaWhitePointTag error and a missing
    * chromaticAdaptationTag.
    */
   PNG_ICC_CHECKSUM(0xf784f3fb, 0x182ea552,
      PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 0, 1/*broken*/,
      "1998/02/09 06:49:00", 3144, "HP-Microsoft sRGB v2 perceptual")

   PNG_ICC_CHECKSUM(0x0398f3fc, 0xf29e526d,
      PNG_MD5(0x00000000, 0x00000000, 0x00000000, 0x00000000), 1, 1/*broken*/,
      "1998/02/09 06:49:00", 3144, "HP-Microsoft sRGB v2 media-relative")
};

static int
png_compare_ICC_profile_with_sRGB(png_const_structrp png_ptr,
   png_const_bytep profile, uLong adler)
{
   /* The quick check is to verify just the MD5 signature and trust the
    * rest of the data.  Because the profile has already been verified for
    * correctness this is safe.  png_colorspace_set_sRGB will check the 'intent'
    * field too, so if the profile has been edited with an intent not defined
    * by sRGB (but maybe defined by a later ICC specification) the read of
    * the profile will fail at that point.
    */

   png_uint_32 length = 0;
   png_uint_32 intent = 0x10000; /* invalid */
#if PNG_sRGB_PROFILE_CHECKS > 1
   uLong crc = 0; /* the value for 0 length data */
#endif
   unsigned int i;

#ifdef PNG_SET_OPTION_SUPPORTED
   /* First see if PNG_SKIP_sRGB_CHECK_PROFILE has been set to "on" */
   if (((png_ptr->options >> PNG_SKIP_sRGB_CHECK_PROFILE) & 3) ==
               PNG_OPTION_ON)
      return 0;
#endif

   for (i=0; i < (sizeof png_sRGB_checks) / (sizeof png_sRGB_checks[0]); ++i)
   {
      if (png_get_uint_32(profile+84) == png_sRGB_checks[i].md5[0] &&
         png_get_uint_32(profile+88) == png_sRGB_checks[i].md5[1] &&
         png_get_uint_32(profile+92) == png_sRGB_checks[i].md5[2] &&
         png_get_uint_32(profile+96) == png_sRGB_checks[i].md5[3])
      {
         /* This may be one of the old HP profiles without an MD5, in that
          * case we can only use the length and Adler32 (note that these
          * are not used by default if there is an MD5!)
          */
#        if PNG_sRGB_PROFILE_CHECKS == 0
            if (png_sRGB_checks[i].have_md5 != 0)
               return 1+png_sRGB_checks[i].is_broken;
#        endif

         /* Profile is unsigned or more checks have been configured in. */
         if (length == 0)
         {
            length = png_get_uint_32(profile);
            intent = png_get_uint_32(profile+64);
         }

         /* Length *and* intent must match */
         if (length == png_sRGB_checks[i].length &&
            intent == png_sRGB_checks[i].intent)
         {
            /* Now calculate the adler32 if not done already. */
            if (adler == 0)
            {
               adler = adler32(0, NULL, 0);
               adler = adler32(adler, profile, length);
            }

            if (adler == png_sRGB_checks[i].adler)
            {
               /* These basic checks suggest that the data has not been
                * modified, but if the check level is more than 1 perform
                * our own crc32 checksum on the data.