[previous] 1891 [next] A composite expression of 'essentially unsigned' type (%1s) is being implicitly converted to a wider unsigned type, '%2s'.
Arithmetic type - Composite expressions

This message is issued whenever a composite expression of essentially unsigned type undergoes a usual arithmetic conversion to a wider unsigned integer type.

It is a common misconception among programmers that the type in which the composite expression is evaluated is influenced by the wider type. Instead, the type of the expression is determined solely from the type of its operands after any integral promotion. Therefore, wraparound may occur, which could be avoided if the operands were cast to the wider type, or rearranged so that wider operands appear first.

For example: 


/*PRQA S 1-9999 ++*/
/*PRQA S 1891 --*/

unsigned f1891 (unsigned short a, unsigned b)
{
  b = (a + 1) + b;          /* 1891 */

  return ((a * 2) - b);     /* 1891 */
}

For the purposes of QAC conversion messages, types are ordered according to the configured size (-s option), by default; hence for a typical 32 bit configuration, types int and long will be considered equivalent. However, when the -strictrank option is specified, types will be ordered according to their rank; consequently int will be considered narrower than long.

MISRA C:2012 Rules applicable to message 1891:

Rule-10.7  (Required) If a composite expression is used as one operand of an operator in which the usual arithmetic conversions are performed then the other operand shall not have wider essential type

QA·C Source Code Analyser 8.1
MISRA C:2012 Compliance Module 1.0
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