In this blog post, we’ll explore how to find the smallest number from a given set of values using an 8086 assembly language program. The following code snippet demonstrates this process:
data segment STRING1 DB 08h,14h,05h,0Fh,09h res db ? data ends code segment assume cs:code, ds:data start: mov ax, data mov ds, ax mov cx, 04h mov bl, 79h LEA SI, STRING1 up: mov al, [SI] cmp al, bl jge nxt mov bl, al nxt: inc si dec cx jnz up mov res,bl int 3 code ends end start
Step-by-Step Explanation:
1. Data Segment:
STRING1: Defines an array of bytes (8-bit values) to store the numbers: 08h, 14h, 05h, 0Fh, 09h.res: Reserves a single byte to store the smallest number found.
2. Code Segment:
Initialization:
mov ax, data: Loads the address of the data segment into the AX register.mov ds, ax: Sets the DS register to point to the data segment, allowing access to variables.mov cx, 04h: Initializes the loop counter CX to 4, as there are 4 numbers to compare.
3. Finding the Smallest Number:
mov bl, 79h: Initializes the BL register to 79h, which is higher than any number in the array, ensuring that any number in the array will be smaller.LEA SI, STRING1: Loads the address of the first element of the STRING1 array into the SI register.
Loop:
mov al, [SI]: Loads the current number from the STRING1 array into the AL register.cmp al, bl: Compares the current number (AL) with the smallest number found so far (BL).jge nxt: If AL is greater than or equal to BL, jump to the next iteration.mov bl, al: If AL is less than BL, update BL with the new smallest number.inc si: Increment the SI register to point to the next number in the array.dec cx: Decrement the loop counter.jnz up: Jump back to the beginning of the loop if CX is not zero.
Storing the Result:
mov res, bl: Stores the smallest number (in BL) into theresvariable.
Program Termination:
int 3: Generates an interrupt 3, which typically halts the program execution.
Overall Process:
- The program initializes the loop counter and a variable to store the smallest number.
- It iterates through each number in the array.
- For each number, it compares it with the current smallest number.
- If the current number is smaller, it updates the smallest number.
- After processing all numbers, the smallest number is stored in the
resvariable. - The program terminates.
Output
C:\TASM>masm smallest.asm
Microsoft (R) Macro Assembler Version 5.00
Copyright (C) Microsoft Corp 1981-1985, 1987. All rights reserved.
Object filename [smallest.OBJ]:
Source listing [NUL.LST]:
Cross-reference [NUL.CRF]:
50836 + 450860 Bytes symbol space free
0 Warning Errors
0 Severe Errors
C:\TASM>link smallest.obj
Microsoft (R) Overlay Linker Version 3.60
Copyright (C) Microsoft Corp 1983-1987. All rights reserved.
Run File [SMALLEST.EXE]:
List File [NUL.MAP]:
Libraries [.LIB]:
LINK : warning L4021: no stack segment
C:\TASM>debug smallest.exe
-g
AX=0B0F BX=0005 CX=0000 DX=0000 SP=0000 BP=0000 SI=0004 DI=0000
DS=0B37 ES=0B27 SS=0B37 CS=0B38 IP=001E NV UP EI PL ZR NA PE NC
0B38:001E CC INT 3
-d 0b37:0000
0B37:0000 08 14 05 0F 09 05 00 00-00 00 00 00 00 00 00 00 ................
0B37:0010 B8 37 0B 8E D8 B9 04 00-B3 79 8D 36 00 00 8A 04 .7.......y.6....
0B37:0020 3A C3 7D 02 8A D8 46 49-75 F4 88 1E 05 00 CC FC :.}...FIu.......
0B37:0030 FE C4 9E FA FE 26 8A 47-0C 2A E4 40 50 8B C3 05 .....&.G.*.@P...
0B37:0040 0C 00 52 50 E8 19 46 83-C4 04 50 8D 86 00 FF 50 ..RP..F...P....P
0B37:0050 E8 6F 70 83 C4 06 B8 CD-05 50 8D 86 00 FF 50 E8 .op......P....P.
0B37:0060 CA 0C 83 C4 04 B8 FF FF-50 8D 86 00 FF 50 8D 46 ........P....P.F
0B37:0070 80 50 E8 4D FA 83 C4 06-0A C0 75 03 E9 7B FF 5E .P.M......u..{.^
-q
Understanding the Memory Dump
The memory dump provided by the -d 0b37:0000 command displays the contents of memory starting from the DS (data segment) base address, which is 0b37:0000 in this case.
Here is the relevant portion of the memory:
0B37:0000 08 14 05 0F 09 05 00 00-00 00 00 00 00 00 00 00
08 14 05 0F 09: These are the values ofSTRING1, matching the array initialized in the data segment.05: This is the value of the variableres, where the smallest value is stored.
Thanks for posting..
why you move 79h into bl what is purpose of 79h?
79h is chosen as an arbitrarily large value to ensure that any number in the array is smaller, allowing the program to correctly find the smallest value. It initializes BL so that comparisons can proceed without errors. As the loop iterates, each number is compared with BL, and if a smaller number is found, BL is updated. By the end of the loop, BL holds the smallest number. An alternative approach is to initialize BL with the first element of the array instead.