utf8mb4

gistfile1.m

#import "NSString+Unicode.h"

@implementation NSString (Unicode)

- (NSUInteger)utf8mb4length {
    const char *bytes= [self UTF8String];
    unsigned int length = [self lengthOfBytesUsingEncoding:NSUTF8StringEncoding];

    unsigned int calc = 0;
    for (int i=0; i<length; i++) {
        if ((unsigned char)bytes[i] < 0x80)  {
            calc++;
        } else if ((unsigned char)bytes[i] < 0xE0) {
            calc++;
            i+=1;
        } else if ((unsigned char)bytes[i] < 0xF0) {
            calc++;
            i+=2;
        } else if ((unsigned char)bytes[i] < 0xF8) {
            calc++;
            i+=3;
        } else if ((unsigned char)bytes[i] < 0xFC) {
            calc++;
            i+=4;
        } else if ((unsigned char)bytes[i] < 0xFE) {
            calc++;
            i+=5;
        }
    }
    return calc;
}

- (NSUInteger)utf8mb4Offset:(NSUInteger)offset {
    const char *bytes= [self UTF8String];
    unsigned int length = [self lengthOfBytesUsingEncoding:NSUTF8StringEncoding];
    
    unsigned int calc = 0;
    for (int i=0; i<length && offset != 0; i++) {
        if ((unsigned char)bytes[i] < 0x80)  {
            offset--;
            calc++;
        } else if ((unsigned char)bytes[i] < 0xE0) {
            offset--;
            calc++;
            i+=1;
        } else if ((unsigned char)bytes[i] < 0xF0) {
            offset--;
            calc++;
            i+=2;
        } else if ((unsigned char)bytes[i] < 0xF8) {
            offset-=2;
            calc++;
            i+=3;
        } else if ((unsigned char)bytes[i] < 0xFC) {
            offset-=2;
            calc++;
            i+=4;
        } else if ((unsigned char)bytes[i] < 0xFE) {
            offset-=2;
            calc++;
            i+=5;
        }
    }
    return calc;
}
@end