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Rules 13.4 Function call with float

Posted: Tue Jun 25, 2013 3:34 pm
by Bfr
Hello,

As the rule 13.4 says : The controlling expression of a for statement shall not contain any objects of floating type.

But what about a function call with a float as parameter (example below) ?

I am asking this in order to implement a MISRA rule checker.

Code: Select all

int32_t i = 0;
float32_t float_var;

[...]

for (i = 0; i < float_to_int(float_var); ++i)
{
[...]
}
It seems correct to me since the float is not really use in the controlling expression. But the rules says any objects and that confuse me a little.

Thanks,
Ben

Re: Rules 13.4 Function call with float

Posted: Thu Sep 12, 2013 9:23 am
by misra-c
Using a floating point object to count or compare loop iterations is not recommended. For some values of the loop limits and increment, the accumulation of rounding errors could result in a number of iterations that differs from the expected number.

There are contexts in which use of floating point objects in a controlling expression might not cause any issues (including the example you cite). However a strict interpretation of MISRA-C:2004 does not permit any such uses.

See also: http://misra.org.uk/forum/viewtopic.php?f=69&t=873

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For MISRA C:2012 this has been clarified in Rule 14.1 and Rule 14.2 - this would allow your example to be compliant, provided that float_to_int(float_var) was invarient