PRACE NPT

#include <stdio.h>

#include <stdlib.h>

int ilog2( int n )

// ---------------------------------------------------------------------

// --- Function 'log2' determines whether the integer input argument

//     is a power of 2. If so, it returns this power.

// ---------------------------------------------------------------------

{

   int m, n1;

// ---------------------------------------------------------------------

   if ( n < 1 ) {

      printf( "*** ERROR: argument %d is not valid\n", n );

      exit( -1 );

   }

   if ( n == 1 ) return( 0 );

   n1 = n;

   m  = 0;

   while( 1 ) {

      if ( ( n1 != 1 ) && ( n1%2 != 0 ) ) {

         printf( "*** ERROR: argument %d is not a power of 2\n", n );

         exit( -1 );

      }

      if ( n1 == 1 ) return( m );

      n1 = n1/2;

      m++;

   }

}