WEBVTT 1 00:01.690 --> 00:03.010 Hello and welcome back. 2 00:03.010 --> 00:05.200 In this lesson, we are going to study DIV. 3 00:05.830 --> 00:07.330 DIV stands for divide. 4 00:08.290 --> 00:11.770 So let's take a look at what is the meaning of DIV. 5 00:12.250 --> 00:21.310 So in this case here, the number that we want to divide is stored in the - and - register. 6 00:22.150 --> 00:25.960 So we need to store in this way - -. 7 00:26.110 --> 00:33.940 So what this means is that - and - registers are combined to form a 128-bit dividend. 8 00:34.450 --> 00:39.520 The DIV instruction then divides this 128-bit value by the specified operand. 9 00:40.300 --> 00:42.010 For example, a register. 10 00:42.640 --> 00:47.770 So the result of the division can be a quotient and the remainder. 11 00:47.770 --> 00:55.930 So the quotient will be placed in the - register and the remainder will be placed in the - register. 12 00:56.830 --> 01:07.090 So - - divided by register gives you the quotient which is placed in - and - - modulus will 13 01:07.090 --> 01:08.260 give you the remainder. 14 01:08.590 --> 01:13.150 There are also exceptions that can occur if you divide with zero. 15 01:13.180 --> 01:19.060 For example, if your divisor is zero, then you will result in an exception. 16 01:19.630 --> 01:25.390 Another exception is where the number that you divide is very big, but the divisor is very small. 17 01:25.600 --> 01:32.680 Then the result will not be able to fit into the quotient, so it causes an integer overflow. 18 01:33.280 --> 01:37.030 So let's take a look at this in the x64dbg. 19 01:37.630 --> 01:39.640 I have opened my template 2X. 20 01:40.180 --> 01:43.570 Now let's try to divide five with two. 21 01:44.780 --> 01:47.210 So let's move. 22 01:51.110 --> 01:53.030 Let's set our - to be zero. 23 01:56.680 --> 02:03.520 And then we move - five, and then we divide. 24 02:03.580 --> 02:04.720 Then we move. 25 02:04.720 --> 02:07.900 Uh, - two. 26 02:09.400 --> 02:11.050 So in this case here. 27 02:11.760 --> 02:15.630 We need to set it to zero because we want to. 28 02:15.630 --> 02:20.040 Because when you divide, it's going to combine the - and - register. 29 02:20.190 --> 02:21.900 So let's start over now. 30 02:21.930 --> 02:23.400 Let's run to our breakpoint. 31 02:25.220 --> 02:26.870 So it is zero. 32 02:28.530 --> 02:29.790 - is zero. 33 02:30.180 --> 02:33.120 And then now - is five. 34 02:33.420 --> 02:39.840 So we are going to divide - combined with -. 35 02:40.140 --> 02:42.960 So that's why we need to set - to be zero. 36 02:43.590 --> 02:47.820 Then we are going to divide it with - which is two. 37 02:47.850 --> 02:48.960 So let's step over. 38 02:49.590 --> 02:51.510 And now - is two. 39 02:52.620 --> 02:56.550 Now we need to perform the division with -. 40 03:00.070 --> 03:05.020 So after dividing, we get the result in the -. 41 03:06.260 --> 03:07.190 And -. 42 03:07.190 --> 03:13.220 So - is your quotient and your - is one, just as expected. 43 03:13.910 --> 03:18.710 Now, the exception that occurs if we divide with zero or divide with a big number. 44 03:18.710 --> 03:20.420 Let's try a big number. 45 03:21.170 --> 03:23.210 So let's say we move. 46 03:30.580 --> 03:33.550 So they are all together here. 47 03:33.550 --> 03:34.660 A QWORD here. 48 03:34.810 --> 03:38.680 I just type in 16 F's, so it's a QWORD there. 49 03:38.710 --> 03:39.640 Very big number. 50 03:40.360 --> 03:44.290 And also do the same thing with -. 51 03:51.140 --> 03:56.450 So now it's a huge number and we are going to divide it with two. 52 03:57.050 --> 03:58.430 Let's do a division now. 53 04:02.220 --> 04:03.270 Let's step over. 54 04:05.150 --> 04:11.030 So it moves this into - and it moves this into -. 55 04:11.030 --> 04:14.780 So now the number that we're dividing is - combined with -. 56 04:14.900 --> 04:17.810 So it becomes a very long number or very big. 57 04:17.960 --> 04:21.020 And then you're going to divide with two. 58 04:21.470 --> 04:24.920 So if you step over, you will see there's an exception mentioned here. 59 04:25.340 --> 04:26.990 Exception integer overflow. 60 04:27.410 --> 04:32.150 Because the result of the division is too big to fit into -. 61 04:32.180 --> 04:33.230 That's why it overflows. 62 04:33.770 --> 04:40.580 So this is how you can implement division inside the x64dbg assembly. 63 04:40.610 --> 04:42.050 That's all for this video. 64 04:42.050 --> 04:43.310 Thank you for watching.