Compilation Tutorial 2 by sssa2000
There is a contradiction with my girlfriend, or the computer is good, you can let me be quiet.
Let us start. Last time I use an example to give everyone a blurred concept, maybe you don't fully understand the way to go to the dragon, this doesn't matter, there is a knowledge, you can.
I think that the biggest obstacle to learning compilation is that the teaching method in the book is not suitable for beginners. Even if there is a foundation, it is a bit confused. Since it is to start from the actual start, we will start our example warm up, and The last time is almost
============================================================================================================================================================================================================= =====================================================================================================================================================
OBJECTIV: To save the multi-character (note that multi-character) entered (note is multi-character) to the variable inbuf composed of several memory cells to end the carriage return.
Code segment
Assume cs: code; no data segment is required because there is no declaration
Start: MOV BX, 00h
Again: MOV AH, 01H; call the interrupt, don't say it, type a character to be ASCII to Al (note is a character)
Int 21h
CMP Al, 0DH; if the value in Al is 0DH,
JZ Stop; turn it to the STOP label
MOV [Inbuf BX], Al; puts Al's data to the address of Inbuf BX
Inc bx; bx = bx 1
JMP Again; jump to the Again Number to accept the next character until the user carries
Stop: MOV AH, 4CH
Int 21h
Code ends
End Start
============================================================================================================================================================================================================= ==============================
The procedure is not long, the initiator is most afraid of a long period of procedure, I am also afraid, now I am afraid, people are lazy.
For this program, talk about MOV, and branch procedures.
Pay attention, background music is good, it is recommended to use my mystery, why? Because I am listening. MOV instruction
Format: MOV destination operand, original operand
Explanation: 1. Immediately, the paragraph register CS cannot be used as a destination operation;
2. The original operands and destination operands cannot be the same as the number of memory operands. The following instructions are wrong
MOV 4H, BL
MOV CS, AX
MOV [1000H], [BX]; [] indicates the address
3, the number of original operands and destination operands must be consistent, the same as the number of single-by-thirds, or the same number of double-bytes, when there is a type of operand in the instruction, the other operand is considered as the same Types of. You can define a memory operand as byte or word type with Byte PTR or Word PTR. When the memory operand is a word type, the register or immediately high byte corresponds to its high address, the low-byte corresponds to the low address.
Explain that byte ptr is the force defined by an operand as a BYTE type, Word PTR is similar, similar to C language ()
What does the last sentence mean? We know, one word = two bytes, in the computer, the storage of the word is in bytes, everyone knows the stack to follow the principle of "advanced", so it is necessary to change the high and low. Example: A word type, the value is: 1234h, in memory location:
| 34h | 34 is the low position of the variable.
| ------- |
| 12H | 12 is the high of the variable.
| --------
| | |
Ok, let's see this sentence. "When the memory opera is a word type, the register or the high-character high byte corresponds to its high address, the low-byte corresponds to the low address." For example,
MOV [2000H], AX
Representation:
| Memory |
| ----------
| 存 a 的 低 低
| ----------
| High AX of AX AH
| ----------
Branch program
It is if ... Then, Goto, etc. Of course, in the assembly, there is no such statement
Let's take a look at the CMP instruction.
Format: CMP destination, original operand
Role: According to the size relationship of the two operands, the status flag value is generated.
JC / JNC Directive
Format: JC / JNC label
Role: JC has a carry, that is, cf = 1 JNC reverse (what is CF? I will explain the computer's register, don't worry)
JP / JNP
The number of JP: 1 is even if the number is turned (pf = 1), the JNP is opposite
JZ / JNZ
JZ: Turn to zero, (zf = 1) JNZ: opposite
JL / JGE
JL: Small than turning (sf <> of or zf = 0) JGE is greater than or equal to turn (sf <= of or zf = 1)
. . . . . . . . There are still many oh, don't write, check your information, don't be too lazy.
There is also one of the most important, JMP unconditional jump instructions, don't explain it?
That example is to look at it, I realized how to jump. Will be harvested ~~
Not addiction? Go another process,
============================================================================================================================================================================================================= ======================= XY absolute value
DSEG segment
X dB 40h
Y db 73h
Z DB?
DSEG Ends
SSEG segment stack; setup stack segment
DB 80H DUP (0)
SSEG Ends
CSEG segment
Assume DS: DSEG, SS: SSEG, CS: CSEG; Is it feeling different from previous? Oh, realize
Start:
MOV AX, DSEG
Mov Al, X
CMP AL, Y; Generate Status Sign according to X-Y
JL XL; Sign number is jumping
SUB Al, Y;
MOV Z, Al; Z = X-Y
XL: MOV BL, Y
SUB BL, Al
MOV Z, BL; Z = Y-X
OK:
MOV AH, 4CH
Int 21h
CSEG Ends
End Start
============================================================================================================================================================================================================= ===========================
Ok, should there be no problem? I still want to talk about some addressing methods. The next chapter needs to tell the basic knowledge, avoid can't avoid it, but now, your understanding of the compilation should be a bit deep, and the compilation is not difficult, is it? If you have this feeling, then my purpose is also reached, and next, we explain the registers, and addressed. Do not speak. Ok, Class Over!
