Main Content

Float conversion overflow

Overflow when converting between floating point data types

expand all in page

Description

This defect occurs when converting a floating point number to a smaller floating point data type. If the variable does not have enough memory to represent the original number, the conversion overflows.

The exact storage allocation for different floating point types depends on your processor. See Target processor type (-target).

Risk

Overflows can result in unpredictable values from computations. The result can be infinity or the maximum finite value depending on the rounding mode used in the implementation. If you use the result of an overflowing conversion in subsequent computations and do not account for the overflow, you can see unexpected results.

Fix

The fix depends on the root cause of the defect. Often the result details show a sequence of events that led to the defect. Use this event list to determine how the variable being converted acquires its current value You can implement the fix on any event in the sequence. If the result details do not show the event history, you can trace back using right-click options in the source code and see previous 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).

You can fix the defect by:

  • Using a bigger data type for the result of the conversion so that all values can be accommodated.

  • Checking for values that lead to the overflow and performing appropriate error handling.

In general, avoid conversions to smaller floating point types.

See examples of fixes below.

If you do not want to fix the issue, 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

expand all

float convert(void) {

    double diam = 1e100;
    return (float)diam;
}

In the return statement, the variable diam of type double (64 bits) is converted to a variable of type float (32 bits). However, the value 1^100 requires more than 32 bits to be precisely represented.

Result Information

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

Version History

Introduced in R2013b

expand all

See Also

| | |

Topics