Re: [PATCH v2] misra: deviate MISRA C Rule 10.1 for boolean operands of arithmetic

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.11.2026 10:25, Dmytro Prokopchuk1 wrote:
> MISRA C Rule 10.1 states: "Operands shall not be of an inappropriate
> essential type".
> 
> The result of relational, equality and logical negation operators has
> type int and value 0 or 1 (C99 6.5.8p6, 6.5.9p3, 6.5.3.3p5). An object
> or function result of type bool has value 0 or 1 too, and it is
> promoted to int (C99 6.3.1.2, 6.3.1.1p2). Using that value as an
> operand of binary +, -, *, <<, >>, <, >, <=, >= and of +=, -=, *=,
> <<=, >>= is well-defined. Division, remainder, unary plus and minus,

We did discuss division and remainder. What's wrong with unary plus and
minus? Unary minus in particular can be used to create a mask value from
a boolean (all bits set or all bits clear). And why would unary plus and
minus be excluded when bitwise complement (which is less useful with a
boolean operand than unary minus) is not?

As to relational operators (which it looks like we didn't discuss in v1):
Is it possible to express anything with them which cannot be expressed
with equality operators? If not, I'd suggest keeping them out as well.

> --- a/automation/eclair_analysis/ECLAIR/deviations.ecl
> +++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
> @@ -335,6 +335,10 @@ still non-negative."
>  -config=MC3A2.R10.1,etypes+={safe, 
> "stmt(operator(logical)||node(conditional_operator||binary_conditional_operator))",
>  "dst_type(ebool||boolean)"}
>  -doc_end
>  
> +-doc_begin="A 0-or-1 Boolean operand of binary +, -, *, <<, >>, <, >, <=, >= 
> and of +=, -=, *=, <<=, >>= is safe. See docs/misra/deviations.rst for the 
> full explanation."
> +-config=MC3A2.R10.1,etypes+={safe, 
> "stmt(operator(add||sub||add_assign||sub_assign||mul||mul_assign||shl||shr||shl_assign||shr_assign||lt||gt||le||ge))",
>  "src_type(ebool||boolean)"}

Imo this wants shortening by making use of regex-es (provided such can be
used here).

Jan