ch2/2-6.c


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#include<stdio.h>

unsigned setbits(unsigned x, unsigned p, unsigned n, unsigned y) {
    // set n bits in x starting at p to rightmost n bits of y
    unsigned offset = (p + 1 - n);
    unsigned y_mask = y & ~(~0 << n);
    unsigned bot = x & ~(~0 << offset);
    unsigned top = (x >> offset << offset) & y_mask;
    unsigned result = top & bot;
    return result;
}

int main() {
    printf("%x\n", setbits(0xaa, 3, 3, 0x33));
}