[PD] iem_sqrt4~ amd_64 crasher puzzle

[Jonathan Wilkes]

Well, Pd-extended 0.43-4 will crash when trying to create [iem_sqrt4~].  (I'm not sure how to tell whether it's using the latest code or not.)
-Jonathan
 

     On Monday, October 6, 2014 10:23 PM, Jonathan Wilkes <jancsika at yahoo.com> wrote:
   

 I'm still a little shaky on type-punning, but here goes:I'm guessing that the author of iemlib_sqrt4~ assumed that sizeof(long) == sizeof(float) == 4.  Then when one sets the value of the type-pun'd variable that new value would be guaranteed to lie within the float's 4-byte boundary.  But since sizeof(long) == 8 on a 64-bit OS, Pd writes another 4 bytes past what's been allocated for that float.  Then... glibc gets angry, and Linux puts Pd to bed.
Is this about right?  If so, what's the solution?  I guess one could use sizeof and have a branch for 32-bit and one for 64, but that seems even worse.
-Jonathan
 

     On Monday, October 6, 2014 6:09 PM, Jonathan Wilkes via Pd-list <pd-list at lists.iem.at> wrote:
   

 Hi list,[iem_sqrt4~] crashes when trying to create on amd_64.  It creates fine on 32 bit linux.
This leads me to believe there is something in the setup routine that makes an assumption that only holds true for a 32bit OS.
The only thing that stands out to me is a function called in the setup routine, posted below.  This looks particularly suspicious to my untrained eye:      *(long *)(&f) = l;Even if that's not causing the crash, what does it do?

And does that or anything stand out to anyone else?
Thanks,Jonathan

static void iem_sqrt4_tilde_maketable(void)
{
  int i;
  t_float f;
  long l;
  
  if(!iem_sqrt4_tilde_exptab)
  {
    iem_sqrt4_tilde_exptab = (t_float *)getbytes(sizeof(t_float) * IEMSQRT4TAB1SIZE);
    for(i=0; i<IEMSQRT4TAB1SIZE; i++)
    {
      l = (i ? (i == IEMSQRT4TAB1SIZE-1 ? IEMSQRT4TAB1SIZE-2 : i) : 1)<< 23;
      *(long *)(&f) = l;
      iem_sqrt4_tilde_exptab[i] = 1.0f/sqrt(f);
    }
  }
  if(!iem_sqrt4_tilde_mantissatab)
  {
    iem_sqrt4_tilde_mantissatab = (t_float *)getbytes(sizeof(t_float) * IEMSQRT4TAB2SIZE);
    for(i=0; i<IEMSQRT4TAB2SIZE; i++)
    {
      f = 1.0f + (1.0f/(t_float)IEMSQRT4TAB2SIZE) * (t_float)i;
      iem_sqrt4_tilde_mantissatab[i] = 1.0f/sqrt(f);
    }
  }
}


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