Emoji detection in NSString

NSString+Emoji.m

@implementation NSString (Emoji)

- (BOOL)isContainingEmoji
{
    __block BOOL returnValue = NO;
    [self enumerateSubstringsInRange:NSMakeRange(0, [self length]) options:NSStringEnumerationByComposedCharacterSequences usingBlock:
     ^(NSString *substring, NSRange substringRange, NSRange enclosingRange, BOOL *stop) {
         const unichar hs = [substring characterAtIndex:0];
         /*
          * Surrogate pair. All surrogates are removed because they can cause problems on the server.
          * Most of them are emoji characters.
          */
         if (0xd800 <= hs && hs <= 0xdbff) {
             if (substring.length > 1) {
                 const unichar ls = [substring characterAtIndex:1];
                 const int uc = ((hs - 0xd800) * 0x400) + (ls - 0xdc00) + 0x10000;
                 if (0x1d000 <= uc && uc <= 0x1f77f) {
                     returnValue = YES;
                 }
             }
         } else {
             /*
              * Previously, this included from U+2100 up to U+26FF, however, most of them are not
              * emoji but rather mere special symbols. They only suspicious ranges are U+23xx and U+26xx.
              * Strip them with a few exceptions for Japanese.
              */
             if ((0x2300 <= hs && hs <= 0x23ff) || (0x2600 <= hs && hs <= 0x26ff))
                 returnValue = YES;

             /*
              * Override special chars, even though they were marked as YES before.
              * U+263B is ☻ and used in Japanese to toggle small hiragana and dakuten.
              *     On keyboard it seems like different char and isn't actually added to the text when toggling.
              * Others are ☆♪⌒, and are part of the basic Japanese keyboard and are widely used there.
              * Allowing these doesn't break anything, character displays fine on all platforms.
              */
             if (hs == 0x263b || hs == 0x2606 || hs == 0x266a || hs == 0x2312)
                 returnValue = NO;
         }
     }];
    return returnValue;
}

@end