Reverse an NSString using XOR swap (import file: https://gist.github.com/StefanLage/febc88228b548689571d)

NSString+Reverse.h

#import <Foundation/Foundation.h>
 
@interface NSString (Reverse)
+(NSString*)stringReverse:(NSString*)str;
@end 

NSString+Reverse.m

#import "NSString+Reverse.h"
#import "NSString+Char.h"
 
@implementation NSString (Reverse)
 
/*
* Reverse a NSSTRing using XOR swap
* which means we need to first convert it as a char pointer to work with bits
*/
+(NSString*)stringReverse:(NSString*)str{
  char *cWord = [str toChar];
  size_t len  = strlen(cWord);
  int start   = 0;
  int end     = (int)len-1;
  while (start<end) {
    cWord[start]  ^= cWord[end];
    cWord[end]    ^= cWord[start];
    cWord[start]  ^= cWord[end];
    start++;
    end--;
  }
  char reverseData[len];
  memcpy(reverseData, cWord, len);
  NSString *reverse = [[NSString alloc] initWithBytes:reverseData
                                               length:sizeof(reverseData)
                                             encoding:NSUTF8StringEncoding];
  return reverse;
}

@end