FLP02-J. Convert integers to floating point for floating point operations

Using integer arithmetic to calculate a value for assignment to a floating-point variable may lead to loss of information. This can be avoided by converting one of the integers in the expression to a floating-point type. When converting integers to floating-point values, it is important to be aware that there may be loss of precision (see INT03-J. Do not cast numeric types to wider floating-point types without range checking).

Noncompliant Code Example

In this noncompliant code example, the division and multiplication operations take place on integers and the result gets converted to floating-point. This causes floating-point variables d, e, and f to be initialized incorrectly because the operations take place before the values of a, b and c are converted to floating-point. The results of the operations are truncated to the nearest integer or may overflow.

short a = 533;
int b = 6789;
long c = 4664382371590123456L;

float d = a / 7;    // d is 76.0 (truncated)
double e = b / 30;  // e is 226.0 (truncated)
double f = c * 2;   // f is -9.1179793305293046E18 because of overflow

Compliant Solution (Floating Point Literal)

This compliant solution eliminates the decimal error in initialization by ensuring that at least one of the operands to the division operation is of the floating-point type.

short a = 533;
int b = 6789;
long c = 4664382371590123456L;

float d = a / 7.0f;       // d is 76.14286
double e = b / 30.;       // e is 226.3
double f = (double)c * 2; // f is 9.328764743180247E18

Compliant Solution

This compliant solution eliminates the initialization errors by storing the integers in the floating-point variables and then performing the arithmetic operations. This ensures that at least one of the operands is a floating-point number, and consequently the operation is performed on floating-point numbers.

short a = 533;
int b = 6789;
long c = 4664382371590123456L;

float d = a;
double e = b;
double f = c;

d /= 7;  // d is 76.14286
e /= 30; // e is 226.3
f *= 2;  // f is 9.328764743180247E18

Exceptions

FLP31-EX1: If it is the programmer's intention to have the operation use integers before the conversion (obviating the need to use the floor() method, for example) it should be clearly documented to help future maintainers understand that this behavior is intentional.

Risk Assessment

Improper conversions between integers and floating point values may yield unexpected results, especially as a result of precision loss. In some cases, these unexpected results may involve overflow, or undefined behavior.