2.59 Bit Expressions

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Problem:

Write a C expression that will yield a word consisting of the least significant byte of x and the remaining bytes of y. For operands x=0x89abcdef and y=0x76543210, this would give 0x765432ef.

expression：

(x & 0xff) | (y & ~0xff)

test：

#include <stdio.h>
#include <assert.h>

int main() {
    size_t mask = 0xff;
    size_t x = 0x89abcdef;
    size_t y = 0x76543210;
    size_t result = (x & mask) | (y & ~mask);
    assert(result==0x765432ef);
}