CSAPP第二章家庭作业2.63

题目

2.63.1

代码

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#include <stdio.h>

unsigned srl(unsigned x, int k) {
	//Perform shift arithmetically
	unsigned xsra = (int)x >> k;
	//将算术右移补符号位替换成0，完成逻辑右移
	xsra &= ((unsigned)-1 >> k);
	return xsra;
}
int sra(int x, int k) {
	//Perform shift logically
	int xsrl = (unsigned)x >> k;
	//将逻辑右移的补高位0替换成算术右移的符号位
	int w = sizeof(int) << 3;	//获取位长w
	int z = 1 << (w - k - 1);	//
	int mark = z - 1;	//
	int right = xsrl & mark;
	int left = ~mark & (~(z&xsrl)+z);	//不理解。
	
	// printf("%x\n", xsrl);
	// printf("%x\n", (z&xsrl));
	// printf("%x\n", (~(z&xsrl)+z));
	return left | right;
}
int main() {
	printf("%x\n", srl(0xF2345678, 8));
	printf("%x\n", sra(0xF2345678, 8));
	return 0;
}

总结

脑短路、好难啊