QA·C Help - 2923

	2923	Suspicious: Left shift operation on expression of unsigned type results in loss of high order bits.

Shift operations

Dataflow analysis has identified a code construct which is suspicious. The code may be entirely safe but further investigation is advisable.

An expression of unsigned type is the subject of a left shift operation and examination of the immediate context suggests that high order bits could sometimes be lost. Is this intended ?

This will happen in the example below unless the parameter 'n' is greater than 0.


/*PRQA S 1278,2017,2983,2986,3120,3199,3227,3381,3408 ++*/
/*******************************/
/* OPTIONS: -s int=16          */
/*******************************/
void foo(int n)
{
   unsigned int un = 4096U;
   int          i;

   for (i = 0; i < n; ++i)
   {
      un = un - 1U;
   }

   un = un << 4;                      /* 2923 */
}

See also:

2920 Constant: Left shift operation on expression of unsigned type results in loss of high order bits.
2921 Definite: Left shift operation on expression of unsigned type results in loss of high order bits.
2922 Apparent: Left shift operation on expression of unsigned type results in loss of high order bits.

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