Re: [Lightning] Understanding the jit_set_ip

[Paolo Bonzini]

On 06/30/2010 05:25 PM, Mathieu Suen wrote:
> Hi
>
> It is more a C related syntax question but here it is.
>
> I don't understand what does it mean:
> #define    jit_set_ip(ptr)            (_jit.x.pc = (ptr), jit_get_ip ())
>
> Especially near the coma.
>
> My guess is if we got:
> a = jit_set_ip(foo);
>
> it is going to be expand in:

No, it expands to

  a = (_jit.x.pc = (ptr), jit_get_ip ())

which is indeed the same as

  _jit.x.pc = (foo);
  a = jit_get_ip();

It's exactly the same syntax that you use for

  for (i = 0, j = strlen (x); i < --j; i++)
    {
      char t = x[i];
      x[i] = x[j];
      x[j] = t;
    }

(typical textbook example for reversing a string) except that in this 
case you're using the result of the comma operator, which is the 
rightmost operand.  That would be "j = strlen (x)" in the example.

Paolo