# V2620\. MISRA\. Value of a composite expression should not be cast to a different essential type category or a wider essential type\.

This diagnostic rule is based on the [MISRA](https://www.misra.org.uk/) \(Motor Industry Software Reliability Association\) software development guidelines\.

This diagnostic rule is relevant only for C\.

The MISRA C standard defines its own type model, called the [essential type model](https://pvs-studio.com/en/blog/terms/7007/)\.

The conversion a composite expression's result to an essential type of a different category—or to a wider type—can cause the loss of the higher bit values\.

The example:

```cpp
int32_t foo(int16_t x, int16_t y)
{
  return (int32_t)(x * y);
}
```

On typical platforms \(x86/ARM\), the `int16_t` corresponds to the `short` type\. During the evaluation, `short` expands to the `int` type\. However, on other platforms \(for example, 16\-bit microcontrollers\), `int16_t` may correspond to the `int`\. Thus, no expansion to 32 bit occurs, which may result in overflow in the multiplication\.

The fixed code:

```cpp
int32_t foo(int16_t x, int16_t y)
{
  return (int32_t)x * y;
}
```

In this case, the expression is evaluated in a wider type, `int32_t`\.

The example:

```cpp
int32_t sum(float x, float y)
{
  return (int32_t)(x + y);
}
```

According to the essential type model, the expression's resulting type belongs to the real floating essential type, while the `int32_t` type belongs to the signed essential type\. Conversion the sum's result to an integer type causes the loss of precision\. The result of adding two `float` type numbers may also be greater than the maximum of the `int32_t` type range\.

The fixed code:

```cpp
float sum(float x, float y)
{
  return x + y;
}
```

To convert the expression result to the `int` type, make sure to:

* check that the converted value is within the type range;
* use a function to round the result to the integer value\.

Within the essential type model, the type of a composite expression is defined as if the no integer promotion to `int` occurred\.