**FIRST EMAIL**/Java and Orbit Balls *****JAVA DISCUSSION***

[Chris27]

Originally Posted by The Lucas

[SIDE RANT] I think you are missing the point (sorry for the pun). The point of pointer arithmetic is to compute the address of an element (the array data structure is optional). If you can get that address by simply adding to a pointer (stored in a register) that is more efficient than computing that address by loading a symbol and adding the result of a multiplication (indexing an array using a variable).[/SIDE RANT]

And as I stated in my earlier post, both cases boil down to a simple lea instruction in assembly

See, here is a small piece of code I just wrote.

 1 #include <stdlib.h>
 2 
 3 int main()
 4 {
 5   int *array = malloc(10 * sizeof(int));
 6   int *ptr;
 7   int i;
 8 
 9   for(i = 0; i < 10; i++)
10     ptr = array + i;
11 
12   return 0;
13 }

and its assembly

0000000000000000 <main>:
   0:	55                   	push   %rbp
   1:	48 89 e5             	mov    %rsp,%rbp
   4:	48 83 ec 20          	sub    $0x20,%rsp
   8:	bf 28 00 00 00       	mov    $0x28,%edi
   d:	e8 00 00 00 00       	callq  12 <main+0x12>
  12:	48 89 45 f8          	mov    %rax,0xfffffffffffffff8(%rbp)
  16:	c7 45 ec 00 00 00 00 	movl   $0x0,0xffffffffffffffec(%rbp)
  1d:	83 7d ec 09          	cmpl   $0x9,0xffffffffffffffec(%rbp)
  21:	7f 19                	jg     3c <main+0x3c>
  23:	8b 45 ec             	mov    0xffffffffffffffec(%rbp),%eax
  26:	48 98                	cltq   
  28:	48 c1 e0 02          	shl    $0x2,%rax
  2c:	48 03 45 f8          	add    0xfffffffffffffff8(%rbp),%rax
  30:	48 89 45 f0          	mov    %rax,0xfffffffffffffff0(%rbp)
  34:	48 8d 45 ec          	lea    0xffffffffffffffec(%rbp),%rax
  38:	ff 00                	incl   (%rax)
  3a:	eb e1                	jmp    1d <main+0x1d>
  3c:	b8 00 00 00 00       	mov    $0x0,%eax
  41:	c9                   	leaveq 
  42:	c3                   	retq

Alternate code

 1 #include <stdlib.h>
 2 
 3 int main()
 4 {
 5   int *array = malloc(10 * sizeof(int));
 6   int *ptr;
 7   int i;
 8 
 9   for(i = 0; i < 10; i++)
10     ptr = &array[i];
11 
12   return 0;
13 }

its assembly

0000000000000000 <main>:
   0:	55                   	push   %rbp
   1:	48 89 e5             	mov    %rsp,%rbp
   4:	48 83 ec 20          	sub    $0x20,%rsp
   8:	bf 28 00 00 00       	mov    $0x28,%edi
   d:	e8 00 00 00 00       	callq  12 <main+0x12>
  12:	48 89 45 f8          	mov    %rax,0xfffffffffffffff8(%rbp)
  16:	c7 45 ec 00 00 00 00 	movl   $0x0,0xffffffffffffffec(%rbp)
  1d:	83 7d ec 09          	cmpl   $0x9,0xffffffffffffffec(%rbp)
  21:	7f 19                	jg     3c <main+0x3c>
  23:	8b 45 ec             	mov    0xffffffffffffffec(%rbp),%eax
  26:	48 98                	cltq   
  28:	48 c1 e0 02          	shl    $0x2,%rax
  2c:	48 03 45 f8          	add    0xfffffffffffffff8(%rbp),%rax
  30:	48 89 45 f0          	mov    %rax,0xfffffffffffffff0(%rbp)
  34:	48 8d 45 ec          	lea    0xffffffffffffffec(%rbp),%rax
  38:	ff 00                	incl   (%rax)
  3a:	eb e1                	jmp    1d <main+0x1d>
  3c:	b8 00 00 00 00       	mov    $0x0,%eax
  41:	c9                   	leaveq 
  42:	c3                   	retq

Absolutely no difference whatsoever.