The C Programming Language 练习题2-6

题目
编写一个函数 setbits(x, p, n, y)，该函数返回对x执行下列操作后的结果值：将x中从第p位开始的n个（二进制）位设置为y中最右边n位的值，x的其余各位保持不变。

题目分析
题目没说从第p位开始是向右还是向左，假设向左。

代码实现

#include <stdio.h>

unsigned setbitstemp(unsigned x, int p, int n, unsigned y);

int main()
{
    int a, b;
    a = 335;
    b = 46;

    printf("x=%d\n", setbitstemp(a, 4, 3, b));
}

unsigned setbitstemp(unsigned x, int p, int n, unsigned y)
{
    int i, j, m;
    i = (x >> p) & (~0 << n);
    j = (y & ~(~0 << n));
    m = i | j;
    x = (m << p) | (x  & ~(~0 << p));
    return x;
}