what is COERCE_FLOAT in ida Hex-Rays' C++ pseudocode?

Question

I was reversing and then i've found a definition as COERCE_FLOAT:

float v28;
float v29;

v29 = COERCE_FLOAT(&v30);
v28 = COERCE_FLOAT(&v31); // what is this?

I've searched and found that it was a simple casting method, but really like it would be in C++?

the value of v30 pass to v29 without the pointer? i don't understand.

Answer 1

I assume it's just a simple cast.

v29 = *reinterpret_cast< float* >( &v30 );

It would be easier if you'd share the generated assembly instead of the pseudo code.

Answer 2

It's probably just a simple cast like WasserEsser said. I encountered this same type of cast while trying to decompile the q_rsqrt function. You could probably recreate the same type of behaviour by using an cast, like WasserEsser suggested, but you could probably also use an union, like in this code :

float Q_rsqrt( float number )
{
    union {
        float f;
        uint32_t i;
    } conv;

    float x2;
    const float threehalfs = 1.5F;

    x2 = number * 0.5F;
    conv.f  = number;
    conv.i  = 0x5f3759df - ( conv.i >> 1 );
    conv.f  = conv.f * ( threehalfs - ( x2 * conv.f * conv.f ) );
    return conv.f;
}

Which then decompiles to this :

float __stdcall Q_rsqrt(float a1)
{
  return (flt1Point5
        - a1
        * flt0Point5
        * COERCE_FLOAT(0x5F3759DF - (SLODWORD(a1) >> 1))
        * COERCE_FLOAT(0x5F3759DF - (SLODWORD(a1) >> 1)))
       * COERCE_FLOAT(0x5F3759DF - (SLODWORD(a1) >> 1));
}