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Float division by zero

Dividing floating point number by zero

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Description

This defect occurs when the denominator of a division operation can be a zero-valued floating point number.

Risk

A division by zero can result in a program crash.

Fix

The fix depends on the root cause of the defect. Often the result details (or source code tooltips in Polyspace as You Code) show a sequence of events that led to the defect. You can implement the fix on any event in the sequence. If the result details do not show this event history, you can search for previous references of variables relevant to the defect using right-click options in the source code and find related events. See also Interpret Bug Finder Results in Polyspace Desktop User Interface or Interpret Bug Finder Results in Polyspace Access Web Interface (Polyspace Access).

It is a good practice to check for zero values of a denominator before division and handle the error. Instead of performing the division directly:

res = num/den;
use a library function that handles zero values of the denominator before performing the division:
res = div(num, den);

See examples of fixes below.

If you do not want to fix the issue, for instance, when you handle infinities in your code, add comments to your result or code to avoid another review. See:

By default, a Bug Finder analysis does not recognize infinities and NaNs. Operations that results in infinities and NaNs might be flagged as defects. To handle infinities and NaN values in your code, use the option Consider non finite floats (-allow-non-finite-floats).

Extend Checker

A default Bug Finder analysis might not raise this defect when the input values are unknown and only a subset of inputs cause an issue. To check for defects caused by specific system input values, run a stricter Bug Finder analysis. See Extend Bug Finder Checkers to Find Defects from Specific System Input Values.

Examples

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float fraction(float num)
{
    float denom = 0.0;
    float result = 0.0;

    result = num/denom;

    return result;
}

A division by zero error occurs at num/denom because denom is zero.

Correction — Check Before Division
float fraction(float num)
{
    float denom = 0.0;
    float result = 0.0;

    if( ((int)denom) != 0)
        result = num/denom;

    return result;
}

Before dividing, add a test to see if the denominator is zero, checking before division occurs. If denom is always zero, this correction can produce a dead code defect in your Polyspace® results.

Correction — Change Denominator

One possible correction is to change the denominator value so that denom is not zero.

float fraction(float num)
{
    float denom = 2.0;
    float result = 0.0;

    result = num/denom;

    return result;
}

Result Information

Group: Numerical
Language: C | C++
Default: On
Command-Line Syntax: FLOAT_ZERO_DIV
Impact: High

Version History

Introduced in R2013b

See Also

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