NSString+Base64.m

//
//  NSStringAdditions.m
//  Gurpartap Singh
//
//  Created by Gurpartap Singh on 06/05/12.
//  Copyright (c) 2012 Gurpartap Singh. All rights reserved.
//

#import "NSString+Base64.h"

static char base64EncodingTable[64] = {
  'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
  'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
  'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
  'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
};

@implementation NSString (Base64Additions)

+ (NSString *)base64StringFromData: (NSData *)data length: (NSUInteger)length {
  unsigned long ixtext, lentext;
  long ctremaining;
  unsigned char input[3], output[4];
  short i, charsonline = 0, ctcopy;
  const unsigned char *raw;
  NSMutableString *result;
  
  lentext = [data length]; 
  if (lentext < 1) {
    return @"";
  }
  result = [NSMutableString stringWithCapacity: lentext];
  raw = [data bytes];
  ixtext = 0; 
  
  while (true) {
    ctremaining = lentext - ixtext;
    if (ctremaining <= 0) {
      break;
    }
    for (i = 0; i < 3; i++) { 
      unsigned long ix = ixtext + i;
      if (ix < lentext) {
        input[i] = raw[ix];
      }
      else {
        input[i] = 0;
      }
    }
    output[0] = (input[0] & 0xFC) >> 2;
    output[1] = ((input[0] & 0x03) << 4) | ((input[1] & 0xF0) >> 4);
    output[2] = ((input[1] & 0x0F) << 2) | ((input[2] & 0xC0) >> 6);
    output[3] = input[2] & 0x3F;
    ctcopy = 4;
    switch (ctremaining) {
      case 1: 
        ctcopy = 2; 
        break;
      case 2: 
        ctcopy = 3; 
        break;
    }
    
    for (i = 0; i < ctcopy; i++) {
      [result appendString: [NSString stringWithFormat: @"%c", base64EncodingTable[output[i]]]];
    }
    
    for (i = ctcopy; i < 4; i++) {
      [result appendString: @"="];
    }
    
    ixtext += 3;
    charsonline += 4;
    
    if ((length > 0) && (charsonline >= length)) {
      charsonline = 0;
    }
  }     
  return result;
}

@end