2.69 Rotate Left

★★★

Problem:

Write code for a function with the following prototype:

/*
 * Do rotating left shift. Assume 0 <= n < w
 * Examples when x = 0x12345678 and w = 32:
 *    n=4 -> 0x23456781, n=20 -> 0x67812345
 */
unsigned rotate_left(unsigned x, int n);

Be careful of the case n=0.

Code:

#include <stdio.h>
#include <assert.h>

unsigned rotate_left(unsigned x, int n) {
    int w = sizeof(int) <<3;
    return (x << n) | (x >> (w - n -1) >> 1);
}

int main() {
    assert(rotate_left(0x12345678, 4)==0x23456781);
    assert(rotate_left(0x12345678, 20)==0x67812345);
    assert(rotate_left(0x12345678, 0)==0x12345678);
    return 0;
}