WEBVTT 1 00:01.730 --> 00:03.440 Hello and welcome back. 2 00:03.440 --> 00:09.350 In this lesson, we are going to take a look at the practical for the XOR operations. 3 00:09.350 --> 00:14.630 And the syntax for XOR operation is: XOR destination, source. 4 00:14.810 --> 00:17.150 And these are two examples. 5 00:17.810 --> 00:25.520 So first, let's put the breakpoint in our template file, which is template 2x, at this location. 6 00:25.970 --> 00:29.750 And then we'll run and hit our breakpoint, 7 00:29.750 --> 00:33.350 and we step over until we come to this line. 8 00:33.620 --> 00:41.960 So here is where we are going to move our initial value to the - register. 9 00:42.860 --> 00:45.020 So we use -. 10 00:45.110 --> 00:49.040 And let's type a move here. 11 00:53.350 --> 00:54.220 Move -, 12 00:56.830 --> 01:00.340 12345678. 13 01:01.090 --> 01:01.420 Okay. 14 01:01.420 --> 01:04.510 Let's say we put this in the - register. 15 01:07.880 --> 01:10.940 So this is the value you want to put to register. 16 01:16.600 --> 01:18.940 I just copy and paste here so you have a copy. 17 01:19.720 --> 01:20.650 Hit okay. 18 01:22.420 --> 01:27.910 And now we step over, and now B3 is in - register. 19 01:27.910 --> 01:29.680 So this is B3 in hex. 20 01:29.830 --> 01:33.010 And we can confirm that with our calculator. 21 01:36.560 --> 01:39.200 Go to hex and type B3. 22 01:44.720 --> 01:47.090 And we see this value here. 23 01:47.630 --> 01:48.260 Same. 24 01:50.340 --> 01:53.340 Now we are going to do something unique. 25 01:53.370 --> 01:56.340 We are going to XOR - with itself. 26 01:58.970 --> 02:01.640 So XOR - with -. 27 02:02.990 --> 02:04.160 See what happens. 28 02:07.170 --> 02:10.860 So we are referring to the second one here, XOR with itself. 29 02:11.280 --> 02:14.160 So when we run this, watch what happens to this. 30 02:15.720 --> 02:16.920 It becomes zero. 31 02:16.920 --> 02:20.760 So this is a very special characteristic of XOR. 32 02:21.030 --> 02:26.190 When you XOR any register with itself, you zero out the register. 33 02:26.310 --> 02:32.610 Now this is very often used in the assembly code because it is more efficient than moving zero to the 34 02:32.610 --> 02:33.330 register. 35 02:33.810 --> 02:35.490 It consumes less bytes. 36 02:36.510 --> 02:39.030 So take note of that. 37 02:39.600 --> 02:42.120 Now, let's do something else. 38 02:42.420 --> 02:48.090 Let's move back this value into the - register. 39 02:58.890 --> 02:59.520 Step over. 40 03:00.840 --> 03:02.580 And now we get back our B3. 41 03:02.580 --> 03:06.480 So now we are going to do another something else which is rather unique. 42 03:06.480 --> 03:11.250 We are going to XOR the register with all ones. 43 03:13.450 --> 03:16.300 So XOR - with all ones. 44 03:19.910 --> 03:22.220 So there are eight bits here of one. 45 03:22.400 --> 03:23.000 Eight ones. 46 03:24.490 --> 03:24.730 Okay. 47 03:26.650 --> 03:30.550 Okay, so we are going to XOR with all ones. 48 03:31.630 --> 03:32.620 Let me check that. 49 03:33.160 --> 03:35.740 Sorry, this should be 0b. 50 03:38.490 --> 03:38.880 All right. 51 03:38.880 --> 03:43.260 So when you convert all ones to hex, it is FF. 52 03:43.710 --> 03:46.350 So let's try this and see what happens. 53 03:46.350 --> 03:47.370 This is the original bit. 54 03:47.370 --> 03:50.040 And now we are going to XOR it with all ones. 55 03:52.140 --> 03:53.220 And we get 4C. 56 03:53.430 --> 03:57.330 So what is 4C in binary? 57 03:57.330 --> 03:59.100 So let's open a calculator. 58 04:01.630 --> 04:08.260 So we can go to hex first. Type 4C. 59 04:09.370 --> 04:13.510 And we see that it is 01001100. 60 04:14.350 --> 04:15.550 This value here. 61 04:16.990 --> 04:18.850 Now what is the significance of that? 62 04:18.850 --> 04:19.330 Take a look. 63 04:19.360 --> 04:21.040 We copy and paste it here. 64 04:28.390 --> 04:32.800 Notice every bit in the original number has been flipped. 65 04:32.800 --> 04:34.630 So one became zero. 66 04:34.810 --> 04:36.220 Zero became one. 67 04:36.760 --> 04:37.180 See that? 68 04:39.460 --> 04:45.190 So there is a significance of XORing any number with all ones. 69 04:45.340 --> 04:47.380 The effect is to flip all the bits. 70 04:48.190 --> 04:48.580 Okay. 71 04:48.580 --> 04:55.030 So this is an example of the register and immediate, and register and register, and also some 72 04:55.030 --> 05:00.820 characteristics of XOR: register with itself, and also XOR of register with all ones. 73 05:00.970 --> 05:02.710 So that's all for this video. 74 05:02.740 --> 05:04.420 Thank you for watching.