Switch Case to Jump Address Table

السلام عليكم ورحمة الله وبركاته,

شكراً جزيلا أخوانى وأخواتى لقد توصلت للحل أثناء بحثى صباحا ..

Consider this switch statement:. 
switch (k) {
case 0:
   k = i + j;
   break;
case 1:
   k = i - j;
   break;
case 4:
   k = i * j;
   break;
default:
   k = j / 2;
   break;
}

It could be implemented by a chain of comparisons, analagous to this C: 
if (k == 0)
   k = i + j;
else if (k == 1)
   k = i - j;
else if (k == 4)
   k = i * j;
else
   k = j / 2;

Can also be implemented by a jump table analagous to this pseudo-C 
address table[] = {label0,label1,label3,label3,label2};
if (k < 0 || k > 4)
	goto label3:
goto table[k];
label0:
   k = i + j;
   goto end;
label1:
   k = i - j;
   goto end;
label2:
   k = i * j;
   goto end;
label3:
   k = j / 2;
end:

You cannot do this in C - it has no datatype to store addresses. You can do it in assembler 

switch:
# assume k in $2
     blt  $2 $0 label3 # if (k < 0)
     li   $8 4         #    goto def;
     bgt  $2 $8 label3 # if (k > 4)
     li   $8 4         #    goto def;
     mul  $8 $2 $8     # offset = k*4;
     lw   $8 table($8)
     jr   $8           # goto table[k];
label0:
     add  $18 $16 $17  # k = i + j;
     j    end          # break;
label1:
    sub  $18 $16 $17   # k = i - j;
     j    end          # break;
label2:
     mul  $18 $16 $17  # k = i * j;
     j    end          # break;
label3:
     div  $18 $17 2    # k = j / 2;
end:...
     .data
table:
     .word label0, label1, label3, label3, label2

If there are many choices a jump table is more efficient.

السلام عليكم،

توضيحاً لتعليمات الأسمبلر التي وردت في المثال الأخير في المشاركة أعلاه

blt = branch if less than

li = load immediate

bgt = branch if greater than

lw = load word

jr = conditional jump

j = unconditional jump

وفيما يلي مثال بالـ x86 instruction set:

include 'win32ax.inc'

.data
table dd 	case1,case2,case3,default

.code
start:
 	mov 	ecx,2 	; ECX = k
 	lea 	eax,[table]
 	mov 	ebx,[eax+ecx*4] ; [Base+Index*Scale] - check: http://www.cs.umbc.edu/courses/undergraduate/CMPE310/Spring04/cpatel2/slides/lab_slides/assem1_extra.pdf
 	jmp 	ebx
 case1:
 	xor 	edx,edx
 	jmp 	fin
 case2:
 	xor 	edx,edx
 	jmp 	fin
 case3:
 	xor 	edx,edx
 	jmp 	fin
 default:
 	xor 	ebx,ebx
 fin:

 	invoke ExitProcess,0

.end start

* الكود يخلص Fasm32

جزاك الله كل خير حقيقى إضافة رائعة أفدتنى كتير وده مش جديد عليك