FLP33-C. Prevent decimal errors when converting from integers to floating point numbers

Conversion from integer types such as char, short, int and long to floating types such as float and double in an assignment statement may lead to loss of information if one of the integer types is not converted to a floating type.

Non-Compliant Code Example

In this non-compliant code, the floating point variables d, e and f are not initialized correctly because the division operation takes place on two integer types and hence the result is truncated to nearest decimal point.

short a = 533;
int b = 6789;
long c = 466438237;

float d = a / 7; /* d is 76.0 */
double e = b / 30; /* e is 226.0 */
double f = c / 789; /*  f is 591176.0 */

Compliant Code Solution 1

In this compliant code, we remove the decimal error in initialization by making the division operation to involve at least one floating point operand. Hence, the result of the operation is the correct floating point number.

short a = 533;
int b = 6789;
long c = 466438237;

float d = a / 7.0f; /* d is 76.14286 */
double e = b / 30.0f; /* e is 226.3 */
double f = c / 789.0f; /* f is 591176.47275 */

Compliant Code Solution 2

In this compliant code, we remove the decimal error in initialization by first storing the integer in the floating point variable and then performing the division operation. This ensures that atleast one of the operands is a floating point number and hence, the result is the correct floating point number.

short a = 533;
int b = 6789;
long c = 466438237;

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

d /= 7; /* d is 76.14286 */
e /= 30; /* e is 226.3 */
f /= 789; /* f is 591176.47275 */

Risk Assessment Summary

References

[Hatton 95] Section 2.7.3, "Floating-point misbehavior"
[ISO/IEC 9899-1999] Section 5.2.4.2.2, "Characteristics of floating types <float.h>"