CSAPP 习题2.49 unsigned_high_prod

// 计算两个32位unsigned乘积的高32位,利用给定的库函数signed_high_prod


#include<iostream>

using namespace std;

unsigned int unsigned_high_prod(unsigned ux, unsigned uy)
{
int sx = (int)ux;
int sy = (int)uy;

// ux = 2^n*SX(n-1) + SX

// uy = 2^n*SY(n-1) + SY

// ux*uy/2^n = SX(n-1)*SY(n-1)*2^n + [ SX(n-1)*SY + SY(n-1)*SX ] + SX*SY/2^n


return unsigned ( (x<0)*sy + (y<0)*sx + signed_high_prod(sx, sy) );

}