1 5dc21454 2023-07-14 jrmu /*
 2 5dc21454 2023-07-14 jrmu  * 2-7. Write a function invert(x,p,n) that returns x with the n bits
 3 5dc21454 2023-07-14 jrmu  * that begin at position p inverted (i.e., 1 changed into 0 and vice versa),
 4 5dc21454 2023-07-14 jrmu  * leaving the others unchanged.
 5 5dc21454 2023-07-14 jrmu  */
 6 5dc21454 2023-07-14 jrmu 
 7 5dc21454 2023-07-14 jrmu #include <stdio.h>
 8 5dc21454 2023-07-14 jrmu 
 9 5dc21454 2023-07-14 jrmu unsigned setbits(unsigned x, int p, int n, unsigned y);
10 5dc21454 2023-07-14 jrmu unsigned getbits(unsigned x, int p, int n);
11 5dc21454 2023-07-14 jrmu unsigned invert(unsigned x, int p, int n);
12 5dc21454 2023-07-14 jrmu 
13 5dc21454 2023-07-14 jrmu main()
14 5dc21454 2023-07-14 jrmu {
15 5dc21454 2023-07-14 jrmu 	printf("%u: %u\n", 0xabcdf0f1, invert(0xabcdef01, 12, 9));
16 5dc21454 2023-07-14 jrmu 	printf("%u: %u\n", 0x1dd45678, invert(0x12345678, 27, 7));
17 5dc21454 2023-07-14 jrmu 	printf("%u: %u\n", 0x92fab03a, invert(0x92fab3da, 9, 5));
18 5dc21454 2023-07-14 jrmu 	printf("%u: %u\n", 0x1babc26a, invert(0x1ba83dea, 17, 11));
19 5dc21454 2023-07-14 jrmu }
20 5dc21454 2023-07-14 jrmu 
21 5dc21454 2023-07-14 jrmu /*
22 5dc21454 2023-07-14 jrmu a    b    c    d    e    f    0    1
23 5dc21454 2023-07-14 jrmu 1010 1011 1100 1101 1110 1111 0000 0001
24 5dc21454 2023-07-14 jrmu 1010 1011 1100 1101 1111 0000 1111 0001
25 5dc21454 2023-07-14 jrmu a    b    c    d    f    0    f    1
26 5dc21454 2023-07-14 jrmu 
27 5dc21454 2023-07-14 jrmu 1    2    3    4    5    6    7    8
28 5dc21454 2023-07-14 jrmu 0001 0010 0011 0100 0101 0110 0111 1000
29 5dc21454 2023-07-14 jrmu 0001 1101 1101 0100 0101 0110 0111 1000
30 5dc21454 2023-07-14 jrmu 1    d    d    4    5    6    7    8
31 5dc21454 2023-07-14 jrmu 
32 5dc21454 2023-07-14 jrmu 9    2    f    a    b    3    d    a
33 5dc21454 2023-07-14 jrmu 1001 0010 1111 1010 1011 0011 1101 1010
34 5dc21454 2023-07-14 jrmu 1001 0010 1111 1010 1011 0000 0011 1010
35 5dc21454 2023-07-14 jrmu 9    2    f    a    b    0    3    a
36 5dc21454 2023-07-14 jrmu 
37 5dc21454 2023-07-14 jrmu 1    b    a    8    3    d    e    a
38 5dc21454 2023-07-14 jrmu 0001 1011 1010 1000 0011 1101 1110 1010
39 5dc21454 2023-07-14 jrmu 0001 1011 1010 1011 1100 0010 0110 1010
40 5dc21454 2023-07-14 jrmu 1    b    a    b    c    2    6    a
41 5dc21454 2023-07-14 jrmu  */
42 5dc21454 2023-07-14 jrmu 
43 5dc21454 2023-07-14 jrmu unsigned invert(unsigned x, int p, int n) {
44 5dc21454 2023-07-14 jrmu 	return setbits(x, p, n, ~getbits(x, p, n));
45 5dc21454 2023-07-14 jrmu }
46 5dc21454 2023-07-14 jrmu 
47 5dc21454 2023-07-14 jrmu unsigned setbits(unsigned x, int p, int n, unsigned y)
48 5dc21454 2023-07-14 jrmu {
49 5dc21454 2023-07-14 jrmu 	return ((x >> (p+1)) << (p+1)) | (getbits(y, n-1, n) << (p-n+1)) | (x & ~(~0 << (p-n+1)));
50 5dc21454 2023-07-14 jrmu }
51 5dc21454 2023-07-14 jrmu 
52 5dc21454 2023-07-14 jrmu unsigned getbits(unsigned x, int p, int n)
53 5dc21454 2023-07-14 jrmu {
54 5dc21454 2023-07-14 jrmu 	return (x >> (p+1-n)) & ~(~0 << n);
55 5dc21454 2023-07-14 jrmu }