hisl_0034: Usage of Signal Routing blocks
R2026bAvoid the ~= operator on floating-point data types in Switch blocks to improve model robustness
Usage: High-Integrity System Modeling
Guideline ID: hisl_0034
Rules
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When using Switch blocks, avoid
comparisons using the Rationale Improve model robustness. Verification Check usage of Signal Routing blocks (Simulink Check) Example — Correct The control input of the Switch block uses a boolean data type with the ~= 0 operator.
Example — Incorrect The control input of the Switch block uses a single (floating-point) data type with the ~= 0 operator.
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Tips
Due to floating-point precision issues, do not test floating-point expressions for inequality (
~=).When the model contains a Switch block computing a relational operator with the
~=operator, the inputs to the block must not be single, double, or any custom storage class that is a floating-point type. Change the data type of the input signals, or rework the model to eliminate using the~=operator within Switch blocks.
Industry Standards
DO-331, Sections MB.6.3.2.g 'Algorithms are accurate'
IEC 61508-3, Table A.3 (3) – 'Language subset'
IEC 61508-3, Table A.4 (3) – 'Defensive programming'
IEC 62304, 5.5.3 - 'Software Unit acceptance criteria'
ISO 26262-6, Table 1 (1b) - 'Use of language subsets'
ISO 26262-6, Table 1 (1d) - 'Use of defensive implementation techniques'
EN 50128, Table A.4 (11) - 'Language Subset'
EN 50128, Table A.3 (1) - 'Defensive Programming'
EN 50657, Table A.4 (11) - 'Language Subset'
EN 50657, Table A.3 (1) - 'Defensive Programming'
EN 50716, Table A.3 (1) 'Defensive Programming'
MISRA C:2012, Dir 1.1
MISRA C:2023, Dir 1.1
