Prevent math errors by carefully bounds-checking before calling functions. In particular, the following domain errors should be prevented by prior bounds-checking:

The calling function should take alternative action if these bounds are violated.

acos( x ), asin( x )

Non-Compliant Code Example

This code may produce a domain error if the argument is not in the range \[-1, \+1\].

float x, result;

result = acos(x);

Compliant Solution

This code uses bounds checking to ensure there is not a domain error.

float x, result;

if( islessequal(x,-1) || isgreaterequal(x, 1) ){
     /* handle domain error */
}

result = acos(x);

atan2( y, x )

Non-Compliant Code Example

This code may produce a domain error if both x and y are zero.

float x, y, result;

result = atan2(y, x);

Compliant Solution

This code tests the arguments to ensure that there is not a domain error.

float x, y, result;

if( fpclassify(x) == FP_ZERO && fpclassify(y) == FP_ZERO){
     /* handle domain error */
}

result = atan2(y, x);

log( x ), log10( x )

Non-Compliant Code Example

This code may produce a domain error if x is negative and a range error if x is zero.

float result, x;

result = log(x);

Compliant Solution

This code tests the suspect arguments to ensure no domain or range errors are raised.

float result, x;

if(islessequal(x, 0)){
     /* handle domain and range errors */
}

result = log(x);

pow( x, y )

Non-Compliant Code Example

This code may produce a domain error if x is zero and y less than or equal to zero. A range error may also occur if x is zero and y is negative.

float x, y, result;

result = pow(x,y);

Compliant Solution

This code tests x and y to ensure that there will be no range or domain errors.

float x, y, result;

if(fpclassify(x) == FP_ZERO && islessequal(y, 0)){
     /* handle domain error condition */
}

result = pow(x, y);

sqrt( x )

Non-Compliant Code Example

This code may produce a domain error if x is negative.

float x, result;

result = sqrt(x);

Compliant Solution

This code tests the suspect argument to ensure no domain error is raised.

float x, result;

if(isless(x, 0)){
     /* handle domain error */
}

result = sqrt(x);

Risk Assessment

Examples of vulnerabilities resulting from the violation of this recommendation can be found on the CERTwebsite.

References

\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 7.12, "Mathematics <math.h>"
\[[Plum 91|AA. C References#Plum 91]\] Topic 2.10, "conv - conversions and overflow"