[Bug c++/27533] wrong result after reinterpret_cast from float* to int*

[pluto at agmk dot net]

------- Comment #5 from pluto at agmk dot net  2006-05-10 15:26 -------
(In reply to comment #0)
> The code
> 
> inline int almost_equal(float a, float b, int maxUlps = 16) {
>   int intDiff = *(reinterpret_cast<int*>(&a)) -
>                     *(reinterpret_cast<int*>(&b));

if you really need such casting and still use strict-aliasing
you should rewrite almost_equal().

/*inline*/ int almost_equal( float a, float b )
{
        int ia;
        memcpy( &ia, &a, sizeof(int) );
        int ib;
        memcpy( &ib, &b, sizeof(int) );
        return ( ia - ib );
}

compiler will optimize it nicely ;)

00000000 <almost_equal(float, float)>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   83 ec 10                sub    $0x10,%esp
   6:   8b 45 08                mov    0x8(%ebp),%eax    <===
   9:   2b 45 0c                sub    0xc(%ebp),%eax    <===
   c:   c9                      leave
   d:   c3                      ret


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27533