[asm] exchange numbers in an array
 

im trying to make a prog in inline asm to find the median of an array of numbers
my last lines are
:"r="(median)
:"r"(size),"r"(n)
:"%eax"etcetc


so %2 is the addr of my array with 'size' elements
i want to sort the array and find the middle element
so im using bubble sort:
variables for bubble loop are i,j stored in eax,edx
mov 0(%2,%%eax,4),%%ebx #ebx=n[i]
mov 0(%2,%%edx,4),%%ecx #ecx=n[j]
if n[i]>n[j]
(i 1st tried)
xchg %%ebx,%%ecx ##this will only exchange values in ecx,ebx,not in the array
(then tried)
mov %%ebx,0(%2,%%edx,4) #n[j]=value of n[i] taken above
mov %%ecx,0(%2,%%eax,4) #similar
(but this didnt work either)

im taking the middle element like this:
mov %1,%%eax
sar $1,%%eax #divide eax by 2
mov 0(%2,%%eax,4),%0 #copy n[i/2] to median

if anyone understood what i asked, plz reply...

If you're trying to exchange two values, the best way to do that is three XOR operations.

xorl %eax, %edx
xorl %ebx, %eax
xorl %eax, %edx

However, the thing to pay attention to is the list of legal operands:
src dst
idata reg
idata mem
reg reg
mem reg
reg mem

So I think what you'd have to do is move both pieces of data from the array to registers, XOR them, then move them back.

However, now that I put more thought into it, that might not answer your solution. I'll give it some more thought.

my program finally ran...why..i dunno
maybe coz of compiler/OS/processor version quirks