Math Operations

hisl_0001: Usage of Abs block

ID: Title	hisl_0001: Usage of Abs block
Description	To support robustness of generated code, when using the Abs block,
	A	Avoid Boolean and unsigned data types as inputs to the Abs block.
	B	Select block parameter Saturate on integer overflow.
Notes	The Abs block does not support Boolean data types. Specifying an unsigned input data type, might optimize the Abs block out of the generated code, resulting in a block you cannot trace to the generated code. For signed data types, Simulink® does not represent the absolute value of the most negative value. When you select Saturate on integer overflow, the absolute value of the data type saturates to the most positive representable value. When you clear Saturate on integer overflow, absolute value calculations in the simulation and generated code might not be consistent or expected.
Rationale	A	Support generation of traceable code.
	B	Achieve consistent and expected behavior of model simulation and generated code.
Model Advisor Checks	Check usage of Abs blocks (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset' IEC 61508-3, Table A.4 (3) 'Defensive programming' IEC 61508-3, Table A.3 (2) 'Strongly typed programming language’ IEC 61508-3, Table B.8 (3) 'Control Flow Analysis' 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' ISO 26262-6, Table 7 (1f) 'Control flow analysis' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' EN 50128, Table A.4 (8) 'Strongly Typed Programming Language' EN 50128, Table A.19 (3) 'Control Flow Analysis' DO-331, Section MB.6.3.2.d 'Low-level requirements are verifiable' DO-331, Section MB.6.3.2.g – 'Algorithms are accurate' MISRA C:2012, Dir 4.1 INT32-C. Ensure that operations on signed integers do not result in overflow
Last Changed	R2021b
Examples	Recommended Not Recommended

hisl_0002: Usage of remainder and reciprocal operations

ID: Title	hisl_0002: Usage of remainder and reciprocal operations
Description	To support robustness of generated code, when using the Math Function block with remainder-after-division (rem) or reciprocal (reciprocal) operations:
	A	Protect the input of the reciprocal function from going to zero.
	B	Protect the second input of the rem function from going to zero.
Note	You can get a divide-by-zero operation, resulting in an infinite (Inf) output value for the reciprocal function, or a Not-a-Number (NaN) output value for the rem function. To avoid overflows or undefined values, protect the corresponding input from going to zero.
Rationale	Protect against overflows and undefined numerical results.
Model Advisor Checks	Check usage of remainder and reciprocal operations (Simulink Check)
References	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(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1 INT33-C. Ensure that division and remainder operations do not result in divide-by-zero errors
Last Changed	R2021b
Examples	In the following example, when the input signal oscillates around zero, the output exhibits a large change in value. You need further protection against the large change in value.

hisl_0003: Usage of square root operations

ID: Title	hisl_0003: Usage of square root operations
Description	To support robustness of generated code, when using the Square Root operations, do one of the following:
	A	Account for complex numbers as the output.
	B	Protect the input from going negative.
Rationale	Avoid undesirable results in generated code.
Model Advisor Checks	Check usage of square root operations (Simulink Check)
References	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(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1
Last Changed	R2021b
Examples

hisl_0028: Usage of Reciprocal Square Root blocks

ID: Title	hisl_0028: Usage of Reciprocal Square Root blocks
Description	To support robustness of generated code, when using the Reciprocal Square Root block, do one of the following:
	A	Protect the input from going negative.
	B	Protect the input from going to zero.
Note	You can get a divide-by-zero operation, resulting in an (Inf) output value for the reciprocal function. To avoid overflows or undefined values, protect the corresponding input from going to zero.
Rationale	A, B	Avoid undesirable results in generated code.
Model Advisor Checks	Check usage of Reciprocal Sqrt blocks (Simulink Check)
References	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(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1 INT33-C. Ensure that division and remainder operations do not result in divide-by-zero errors
Last Changed	R2021b
Examples

hisl_0004: Usage of natural logarithm and base 10 logarithm operations

ID: Title	hisl_0004: Usage of natural logarithm and base 10 logarithm operations
Description	To support robustness of generated code, when using the math operations like natural logarithm (log) or base 10 logarithm (log10) :
	A	Protect the input from going negative.
	B	Protect the input from equaling zero.
	C	Account for complex numbers as the output value.
Notes	If you set the output data type to complex, the natural logarithm and base 10 logarithm functions output complex values for negative input values. If you set the output data type to real, the functions output NAN for negative numbers, and minus infinity (-inf) for zero values.
Rationale	A, B, C	Support generation of robust code.
Model Advisor Checks	Check usage of log and log10 operations (Simulink Check)
References	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' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1 INT33-C. Ensure that division and remainder operations do not result in divide-by-zero errors
Last Changed	R2024a
Examples	You can protect against: Negative numbers using an Abs block. Zero values using a combination of the MinMax block and a Constant block, with Constant value set to eps (epsilon). The following example displays the resulting output for input values ranging from -100 to 100.

hisl_0005: Usage of Product blocks

ID: Title	hisl_0005: Usage of Product blocks
Description	When the Product block parameter Multiplication is set to Matrix(*), protect divisor inputs from becoming singular input matrices.
Notes	When using Product blocks to compute the inverse of a matrix, or a matrix division, you might get a divide by a singular matrix. This division results in a NaN output. To avoid overflows, protect divisor inputs from becoming singular input matrices.
Rationale	Protect against overflows and support robustness of generated code.
Model Advisor Checks	Adherence to this modeling guideline cannot be verified by using a Model Advisor check.
References	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' DO-331, Section MB.6.3.2.g 'Algorithms are accurate MISRA C:2012, Dir 4.1
Prerequisites	hisl_0314: Configuration Parameters > Diagnostics > Data Validity > Signals
Last Changed	R2021a

hisl_0029: Usage of Assignment blocks

ID: Title	hisl_0029: Usage of Assignment blocks
Description	To support robustness of generated code, when using the Assignment block, initialize array fields before their first use.
Notes	If the output vector of the Assignment block is not initialized with an input to the block, elements of the vector might not be initialized in the generated code. When the Assignment block is used iteratively and array fields are assigned during one simulation time step, you do not need initialization input to the block. Accessing uninitialized elements of block output can result in unexpected behavior. For a partial write operations, maintain a persistent output buffer (for example, see cgsl_0408: Partial data send for component deployment).
Rationale	Avoid undesirable results in generated code.
Model Advisor Checks	Check usage of Assignment blocks (Simulink Check)
References	IEC 61508-3, Table A.3 (3) 'Language subset’ IEC 61508-3, Table A.4 (3) 'Defensive programming’ IEC 61508-3, Table A.3 (2) ‘Strongly typed programming language’ IEC 62304, 5.5.3 - Software Unit acceptance criteria ISO 26262–6, Table 1(b) 'Use of language subsets' ISO 26262–6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' EN 50128, Table A.4 (8) 'Strongly Typed Programming Language' DO-331, Section MB.6.3.2.g – 'Algorithms are accurate' MISRA C:2012, Rule 9.1 EXP33-C. Do not read uninitialized memory
Last Changed	R2023a
Examples	Not Recommended: No initialization input Y0 when block is not used iteratively Recommended: Initialization input Y0 when block is not used iteratively Recommended: Initialize array fields when block is used iteratively

hisl_0066: Usage of Gain blocks

ID: Title	hisl_0066: Usage of Gain blocks
Description	To support traceability of generated code, the value of the Gain block must not resolve to 1.
Notes	The code generation process can remove Gain values equal to 1 during optimization, resulting in model elements with no traceable code. An exception to this rule is setting the Gain value to a named parameter data object with a non-auto storage class.
Rationale	Support the generation of traceable code.
Model Advisor Checks	Check usage of Gain blocks (Simulink Check)
References	DO-331, Section MB 6.3.2.b 'Low-level requirements are accurate and consistent' IEC 61508-3, Table A.3 (3) 'Language subset' IEC 61508-3, Table A.4 (3) 'Defensive programming' IEC 61508-3, Table B.8 (3) 'Control Flow Analysis' 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' ISO 26262-6, Table 7 (1f) 'Control flow analysis' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' EN 50128, Table A.19 (3) 'Control Flow Analysis'
Last Changed	R2018a

hisl_0067: Protect against divide-by-zero calculations

ID: Title	hisl_0067: Protect against divide-by-zero calculations
Description	To support robustness of generated code, when performing divide operations, protect the divisor from going to zero.
Note	To prove that division-by-zero is not possible, perform a static analysis of the model. If division-by-zero is possible, implement one of the following. Using more than one option can result in redundant protection operations: Execute the divide-by-zero Model Advisor check Modify the code generation process to use Code Replacement Libraries (CRLs) For integer-based operations, clear configuration parameter Remove code that protects against division arithmetic exceptions (Embedded Coder) Using CRLs or clearing configuration parameter Remove code that protects against division arithmetic exceptions (Embedded Coder) protects division operations against divide-by-zero operations. However, this action does introduce additional computational and memory overhead, as well as the potential to introduce unreachable code.
Rationale	Improve code compliance of generated code
Model Advisor Checks	Check for divide-by-zero calculations (Simulink Check)
References	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(b) 'Use of language subsets' ISO 26262-6, Table 1(d) 'Use of defensive implementation techniques' EN 50128, Table A.4 (11) 'Language Subset' EN 50128, Table A.3 (1) 'Defensive Programming' DO-331, Section MB.6.3.2.g 'Algorithms are accurate' MISRA C:2012, Dir 4.1
See Also	What Is Code Replacement? (Simulink Coder) Code Replacement Libraries (Simulink Coder) hisl_0054: Configuration Parameters > Code Generation > Optimization > Remove code that protects against division arithmetic exceptions
Last Changed	R2021a
Example	Incorrect Division operation can result in a divide-by-zero scenario. Correct Graphical function to model divide-by-zero check.