Programming in C

Bit Operators
289
Program 12.3 Continued
unsigned int shift (unsigned int value, int n)
{
if ( n > 0 ) // left shift
value = -n;
}
return value;
int main (void)
{
unsigned int w1 = 0177777u, w2 = 0444u;
unsigned int shift (unsigned int value, int n);
printf ("%o\t%o\n", shift (w1, 5), w1 > 6);
printf ("%o\t%o\n", shift (w2, 0), w2 >> 0);
printf ("%o\n", shift (shift (w1, -3), 3));
}
return 0;
Program 12.3 Output
7777740 7777740
1777 1777
444 444
177770
The shift function shown in Program 12.3 declares the type of the argument value to
be unsigned int, thus ensuring that a right shift of value will be zero filled; in other
words, performed as a logical right shift.
If the value of n, which is the shift count, is greater than zero, the function shifts
value left n bits. If n is negative (or zero), the function performs a right shift, where the
number of places that value is shifted is obtained by negating the value of n.
The first call to the shift function from the main routine specifies that the value of
w1 is to be left shifted five bits.The printf call that displays the result of the call to the
shift function also displays the result of directly shifting w1 left five places so that these
values can be compared.
The second call to the shift function has the effect of shifting w1 six places to the
right.The result returned by the function is identical to the result obtained by directly
shifting w1 to the right six places, as verified by the program’s output.