Assembly Language Coding Problems using the alphabet? Please help. Thanks. Assem

Question

Assembly Language Coding Problems using the alphabet? Please help. Thanks.

Assemble, link, and run the "printAlpha.s" (shown at bottom) assembly language program using the following steps:

1) as printAlpha.s -o printAlpha.o
2) gcc printAlpha.o
3) ./a.out

The program prints the alphabetical characters from 'a' to 'z' on one line as follows:

Make 2 copies of the printAlpha.s file, and call them mountainTerrain.s, and triangle.s

PROBLEMS:

Problem 1: Edit the mountainTerrain.s file and change the code to alternature between upper and lower case characters while printing the alphabet. The output should be as follows:

Problem 2: Edit the triangle.s file and change the code to print a triangle using lower case characters. The output should be as follows:

printAlpha.s file in text format:

.intel_syntax noprefix
.data
n1:
.int 97
n2:
.int 122

.text
.globl main

main: mov ebx, DWORD PTR n1
loop: cmp ebx, DWORD PTR n2
jg end
      mov edi, ebx
      call putchar
      inc ebx
      jmp loop
end:      mov edi, 10
      call putchar
      mov eax, 0
      ret

$ ./a.out
abcdefghijklmnopqrstuvwxyz
$ .intel syntax noprefix .data 97 4 5 n2: 6 7 8 .int .int 122 .text .globl main 11 main:mov 12 loopmp 13 mov call inc mp mov call mov ret ebx, DWORD PTR nl ebx, DWORD PTR n2 end edi, ebx putchar ebx loop edi, 10 putchar eax, 0 17 18 end: 19 20 21

Explanation / Answer

Problem 1)

Solution 1: Use conditional branch to output alternatively upper and lower case letters.

.intel_syntax noprefix

.data

n1:

.int 97

n2:

.int 122

.text

.globl main

main:

mov ebx, DWORD PTR n1

loop:

cmp ebx, DWORD PTR n2

jg end

cmp ebx, 97

jge ucase

add ebx, 32

mov edi, ebx

call putchar

inc ebx

jmp loop

ucase:

sub ebx, 32

mov edi, ebx

call putchar

inc ebx

jmp loop

end: mov edi, 10

call putchar

mov eax, 0

ret

Solution 2: You can use another variable as flag whose value will toggle between 0 or 1. Consider when this flag is 0 then print uppercase letter or if 1 then print lowercase letters. Initialize the flag as 0.

.intel_syntax noprefix

.data

n1:

.int 97

n2:

.int 122

.text

.globl main

main:

mov ebx, DWORD PTR n1

mov     ecx, 0

loop:

cmp ebx, DWORD PTR n2

jg end

cmp ecx, 0

je ucase

add ebx, 32

mov edi, ebx

call putchar

inc ebx

mov     ecx, 0

jmp loop

ucase:

sub ebx, 32

mov edi, ebx

call putchar

inc ebx

mov     ecx, 1

jmp loop

end: mov edi, 10

call putchar

mov eax, 0

ret

Problem 2) Create two loops, outer loop will execute 26 time to print the series and inner loop will execute edx-ecx times so as ecx increases number of times inner loop executes decreases.

.intel_syntax noprefix
.data
n1:
.int 97
n2:
.int 122

.text
.globl main

main: mov       ecx, 0

mov     edx, 26

LOOP:

cmp     ecx, 26

bge      end

mov ebx, DWORD PTR n1
sub      edx, edx, ecx

LOOP2:

cmp edx, 0
jle INCR

mov edi, ebx
call putchar
inc ebx

dec      edx
jmp LOOP2

INCR:

inc       ecx

jmp     LOOP

end:      mov edi, 10
      call putchar
      mov eax, 0
      ret

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