Question

Using x86 assembly language, create a flowchart and write an example of code that will sort 2 arrays of unsigned doubleword integers in ascending order and output the largest element in each array. Any sorting procedure can be used, but this procedure must be called twice for each array. The first time it is called, the first array should be sorted and the second time it is called, the second array must be sorted. As well as outputting which is largest in each array.

You can use these unsigned doubleword integers in the example.

Array 1: 00000000, 84728372, E222111F

Array 2: 81002346, 22222222, FFFFFFFF

Answer 1

Assuming that the numbers are stored from memory address 2000 : 501 and the size of the array n is stored in 2000:500.

Algorithm -

1. Load data from offset 500 to register CL (for count).
2. Travel from starting memory location to last and compare two numbers if first number is greater than second number then swap them.
3. First pass fix the position for last number.
4. Decrease the count by 1.
5. Again travel from starting memory location to (last-1, by help of count) and compare two numbers if first number is greater than second number then swap them.
6. Second pass fix the position for last two numbers.
7. Repeat.

MEMORY ADDRESS	MNEMONICS	COMMENT
400	MOV SI, 500	SI<-500
403	MOV CL, [SI]	CL<-[SI]
405	DEC CL	CL<-CL-1
407	MOV SI, 500	SI<-500
40A	MOV CH, [SI]	CH<-[SI]
40C	DEC CH	CH<-CH-1
40E	INC SI	SI<-SI+1
40F	MOV AL, [SI]	AL<-[SI]
411	INC SI	SI<-SI+1
412	CMP AL, [SI]	AL-[SI]
414	JC 41C	JUMP TO 41C IF CY=1
416	XCHG AL, [SI]	SWAP AL AND [SI]
418	DEC SI	SI<-SI-1
419	XCHG AL, [SI]	SWAP AL AND [SI]
41B	INC SI	SI<-SI+1
41C	DEC CH	CH<-CH-1
41E	JNZ 40F	JUMP TO 40F IF ZF=0
420	DEC CL	CL<-CL-1
422	JNZ 407	JUMP TO 407 IF ZF=0
424	HLT	END

Explanation –

1. MOV SI, 500: set the value of SI to 500.
2. MOV CL, [SI]: load data from offset SI to register CL.
3. DEC CL: decrease value of register CL BY 1.
4. MOV SI, 500: set the value of SI to 500.
5. MOV CH, [SI]: load data from offset SI to register CH.
6. DEC CH: decrease value of register CH BY 1.
7. INC SI: increase value of SI BY 1.
8. MOV AL, [SI]: load value from offset SI to register AL.
9. INC SI: increase value of SI BY 1.
10. CMP AL, [SI]: compares value of register AL and [SI] (AL-[SI]).
11. JC 41C: jump to address 41C if carry generated.
12. XCHG AL, [SI]: exchange the contents of register AL and SI.
13. DEC SI: decrease value of SI by 1.
14. XCHG AL, [SI]: exchange the contents of register AL and SI.
15. INC SI: increase value of SI by 1.
16. DEC CH: decrease value of register CH by 1.
17. JNZ 40F: jump to address 40F if zero flat reset.
18. DEC CL: decrease value of register CL by 1.
19. JNZ 407: jump to address 407 if zero flat reset.
20. HLT: stop.