i have 2 nsdata objects, data1 , data2, , i'd bit-wise xor , store result in third nsdata object, xordata.
the first thing tried this:
*data1.bytes^*data2.bytes; but gave error of:
invalid operands binary expression ('const void' , 'const void')
so tried write function extract bytes of data array of integers, perform xor on integers, save result nsdata object. function looks this:
+(nsdata *) dataxor1:(nsdata *) data1 dataxor2:(nsdata *)data2{ const int *data1bytes = [data1 bytes]; const int *data2bytes = [data2 bytes]; nsmutablearray *xorbytes = [[nsmutablearray alloc] init ]; (int = 0; < data1.length;i++){ [xorbytes addobject:[nsnumber numberwithint:(data1bytes[i]^data2bytes[i])]]; } nsdata *xordata = [nskeyedarchiver archiveddatawithrootobject:xorbytes]; return xordata; } this runs, gives wrong answers. when test on 2 simple pieces of data (data1 = 0x7038 , data2 = 0x0038), , use nslog output values are, get:
data1bytes[0] = 8070450532247943280 data2bytes[0] = 8070450532247943168 data1bytes[0]^data2bytes[0] = 112 data1bytes[1] = 10376302331560798334 data2bytes[1] = 10376302331560798334 data1bytes[1]^data2bytes[1] = 0 this boggles mind bit because values in dataxbytes arrays totally wrong, they're xor-ing right values! (0x70 ^ 0x00 = 0x70 = 112)
i think might endian-ness problem, when change initialization of data1bytes to:
const int *data1bytes = cfswapint32bigtohost([data1 bytes]); it runs error when tries access it, saying:
thread 1: exc_bad_access(code=1, address = 0xa08ad539)
is there simpler way xor? if not, how can fix endian problem?
casting int archiving nsarray of nsnumbers not create result you're looking for. you'll want have mutable nsdata append individual bytes to, like
+(nsdata *) dataxor1:(nsdata *) data1 dataxor2:(nsdata *)data2{ const char *data1bytes = [data1 bytes]; const char *data2bytes = [data2 bytes]; // mutable data individual xor'd bytes added nsmutabledata *xordata = [[nsmutabledata alloc] init]; (int = 0; < data1.length; i++){ const char xorbyte = data1bytes[i] ^ data2bytes[i]; [xordata appendbytes:&xorbyte length:1]; } return xordata; } 