1 /*
2  * 2-8. Write a function rightrot(x,n) that returns the value of the
3  * integer x rotated to the right by n bit positions.
4  */
5 
6 #include <stdio.h>
7 
8 unsigned setbits(unsigned x, int p, int n, unsigned y);
9 unsigned getbits(unsigned x, int p, int n);
10 unsigned invert(unsigned x, int p, int n);
11 unsigned rightrot(unsigned x, int n);
12 
13 main()
14 {
15 	printf("%u: %u\n", 0xf01abcde, rightrot(0xabcdef01, 12));
16 	printf("%u: %u\n", 0x468acf02, rightrot(0x12345678, 27));
17 	printf("%u: %u\n", 0xed497d59, rightrot(0x92fab3da, 9));
18 	printf("%u: %u\n", 0x1ef50dd4, rightrot(0x1ba83dea, 17));
19 }
20 /*
21 a    b    c    d    e    f    0    1
22 1010 1011 1100 1101 1110 1111 0000 0001
23 1111 0000 0001 1010 1011 1100 1101 1110
24 f    0    1    a    b    c    d    e
25 
26 1    2    3    4    5    6    7    8
27 0001 0010 0011 0100 0101 0110 0111 1000
28 0100 0110 1000 1010 1100 1111 0000 0010
29 4    6    8    a    c    f    0    2
30 
31 9    2    f    a    b    3    d    a
32 1001 0010 1111 1010 1011 0011 1101 1010
33 1110 1101 0100 1001 0111 1101 0101 1001
34 e    d    4    9    7    d    5    9
35 
36 1    b    a    8    3    d    e    a
37 0001 1011 1010 1000 0011 1101 1110 1010
38 0001 1110 1111 0101 0000 1101 1101 0100
39 1    e    f    5    0    d    d    4
40  */
41 unsigned rightrot(unsigned x, int n) {
42 	return (x >> n) | setbits(0,31,n,x);
43 }
44 
45 unsigned invert(unsigned x, int p, int n) {
46 	return setbits(x, p, n, ~getbits(x, p, n));
47 }
48 
49 unsigned setbits(unsigned x, int p, int n, unsigned y)
50 {
51 	return ((x >> (p+1)) << (p+1)) | (getbits(y, n-1, n) << (p-n+1)) | (x & ~(~0 << (p-n+1)));
52 }
53 
54 unsigned getbits(unsigned x, int p, int n)
55 {
56 	return (x >> (p+1-n)) & ~(~0 << n);
57 }