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PWR044: Avoid unnecessary floating-point data conversions involving constants

Issue​

Mixing float type value with double type constants results in unnecessary data conversions.

Actions​

Instead of the double constant, explicitly specify a float constant by appending the constant with f.

Relevance​

According to the C/C++ standard, binary operators (+, -, *, /, %, <, >, <=, >=, ==, !=) involving a float value and a double constant can often result in unnecessary data conversions: the float value is first promoted to a double, then the binary operator is evaluated. Most of the time this is not the intended behavior.

Code example​

Have a look at the following code:

float example(float a) {
  return a * 2.2;
}

During the evaluation of the expression a * 2.2, the following happens:

  • First, the floating point in variable a is promoted from float to double;

  • Second, multiplication is performed using doubles;

  • And third, the resulting value is converted back to float.

In this particular example, there are two unnecessary conversions: one is promoting a to double, and the other is promoting the result of multiplication a * 2.2 back to float. The solution is to use a float constant 2.2f instead of the double constant 2.2.

float example(float a) {
  return a * 2.2f;
}

References​