from:http://stackoverflow.com/questions/19859388/how-can-i-get-the-ios-device-cpu-architecture-in-runtime

#include <sys/types.h>
#include <sys/sysctl.h>
#include <mach/machine.h>

NSString *getCPUType(void)
{
    NSMutableString *cpu = [[NSMutableString alloc] init];
    size_t size;
    cpu_type_t type;
    cpu_subtype_t subtype;
    size = sizeof(type);
    sysctlbyname("hw.cputype", &type, &size, NULL, 0);

    size = sizeof(subtype);
    sysctlbyname("hw.cpusubtype", &subtype, &size, NULL, 0);

    // values for cputype and cpusubtype defined in mach/machine.h
    if (type == CPU_TYPE_X86)
    {
            [cpu appendString:@"x86 "];
             // check for subtype ...

    } else if (type == CPU_TYPE_ARM)
    {
            [cpu appendString:@"ARM"];
            switch(subtype)
            {
                    case CPU_SUBTYPE_ARM_V7:
                    [cpu appendString:@"V7"];
                    break;
                    // ...
            }
    }
    return [cpu autorelease];
}

- (NSString *)getCPUType {
      NSMutableString *cpu = [[NSMutableString alloc] init];
      size_t size;
      cpu_type_t type;
      cpu_subtype_t subtype;
      size = sizeof(type);
      sysctlbyname("hw.cputype", &type, &size, NULL, 0);

      size = sizeof(subtype);
      sysctlbyname("hw.cpusubtype", &subtype, &size, NULL, 0);

      // values for cputype and cpusubtype defined in mach/machine.h
      if (type == CPU_TYPE_X86_64) {
          [cpu appendString:@"x86_64"];
      } else if (type == CPU_TYPE_X86) {
          [cpu appendString:@"x86"];
      } else if (type == CPU_TYPE_ARM) {
          [cpu appendString:@"ARM"];
          switch(subtype)
          {
              case CPU_SUBTYPE_ARM_V6:
                  [cpu appendString:@"V6"];
                  break;
              case CPU_SUBTYPE_ARM_V7:
                  [cpu appendString:@"V7"];
                  break;
              case CPU_SUBTYPE_ARM_V8:
                  [cpu appendString:@"V8"];
                  break;
          }
      }
      return cpu; 
  }