[mweeks@gsuad.gsu.edu@snowball ~]$ cat table_select.asm 
; Assemble:	  nasm -f elf64 table_select.asm
; Link:		  gcc table_select.o -o table_select

; Based on code from Irvine's chapter 6, slides 59--61.
; This is expanded into a program and adapted for NASM.  -MCW

    extern  printf      ; We will use this external function
    extern  puts        ; We will use this external function


    section .data       ; Data section, initialized variables
CaseTable: db 'A' ; lookup value
    dq Process_A
    EntrySize equ ($ - CaseTable)
    db 'B'
    dq Process_B
    db 'C'
    dq Process_C
    db 'D'
    dq Process_D
NumberOfEntries equ ($ - CaseTable) / EntrySize

mystr1:   db "Process %c", 10, 0
mystr2:   db "Finished", 10, 0


    section .text
    global main
main:
    mov al, 'B'                ; test if B works

    mov ebx,CaseTable          ; point EBX to the table
    mov ecx,NumberOfEntries    ; loop counter
L1: cmp al,[ebx]               ; match found?
    jne L2                     ; no: continue
    call NEAR [ebx + 1]        ; yes: call the procedure
    call WriteString           ; display message
    jmp L3                     ; and exit the loop
L2: add ebx,EntrySize          ; point to next entry
    loop L1                    ; repeat until ECX = 0
L3:
    mov  rax, 0
    ret

Process_A:
   push  rbx
   push  rcx
   mov   rsi, 'A'             ; print the letter A 
   mov   rax, 0
   mov   rdi, mystr1    
   call  printf
   pop   rcx
   pop   rbx
   ret 

Process_B:
   push  rbx
   push  rcx
   mov   rsi, 'B'             ; print the letter B 
   mov   rax, 0
   mov   rdi, mystr1    
   call  printf
   pop   rcx
   pop   rbx
   ret 

Process_C:
   push  rbx
   push  rcx
   mov   rsi, 'C'             ; print the letter C 
   mov   rax, 0
   mov   rdi, mystr1    
   call  printf
   pop   rcx
   pop   rbx
   ret 

Process_D:
   push  rbx
   push  rcx
   mov   rsi, 'D'             ; print the letter D 
   mov   rax, 0
   mov   rdi, mystr1    
   call  printf
   pop   rcx
   pop   rbx
   ret 

WriteString:
   push  rbx
   push  rcx
   mov   rdi, mystr2    
   call  puts
   pop   rcx
   pop   rbx
   ret 

[mweeks@gsuad.gsu.edu@snowball ~]$ nasm -f elf64 table_select.asm
[mweeks@gsuad.gsu.edu@snowball ~]$ gcc table_select.o -o table_select
[mweeks@gsuad.gsu.edu@snowball ~]$ ./table_select
Process B
Finished

[mweeks@gsuad.gsu.edu@snowball ~]$