C language Setbits,invert

K&r Exercise 2-6,setbits (x,p,n,y), set the n bits from the p bit in x to the rightmost n-bit value in Y, and the rest of the x remain unchanged.

#include <stdio.h>unsigned setbits (unsigned x, int p, int n,unsigned y) {    int mask;    int pos=p+1-n;    mask=~ (~0<<n) << pos;    X=x & ~mask;    Y=y<<pos & mask;    X=x|y;        return x;} Main () {    int x=012;    int y=077;    printf ("%o\n", Setbits (X,4,3,y));}

All the bits of the ~0 are 1, by the displacement of 0, to establish a shield code, in-place operation is very common

2-7,invert (X,p,n)

#include <stdio.h>unsigned invert (unsigned x, int p, int n) {    return x^ (~ (~0<<n) << (P+1-n));} int main () {    unsigned a=034;    printf ("%o\n", Invert (a,4,3));}

With 1 bitwise XOR, in-situ inversion; with 0 xor, in situ unchanged

C language Setbits,invert