c - 实现 Booth 算法时的位移位和类型转换问题

Question

我正在编写一个实现 Booth's Algorithm 的程序乘以整数。我只被允许使用位级运算符、逻辑运算符和位移位。我允许程序有一个循环，以及一个将添加两个整数的函数。我无法理解我的程序出了什么问题。当我使用按位运算符来屏蔽 long long 的一半时，我得到了不正确的值。关于我在那里做错了什么的任何建议？也许我不明白如何正确掩饰。它也可能与类型转换有关；我真的不确定。在此先感谢您的帮助!

代码如下:

#include <stdio.h>

int Add (int x, int y);
long long Booth (int x, int y);

int main() {
    int hex1, hex2;
    long long product;
    printf("\nEnter Multiplicand & Multiplier in hex: ");
    scanf(" %x %x", &hex1, &hex2);

    product = Booth(hex1, hex2);

    printf("Multiplicand = 0x%08X \tAs signed = %+d\n", hex1, hex1);
    printf("Multiplier = 0x%08X \tAs signed = %+d\n", hex2, hex2);
    printf("Product = 0x%16X \tAs signed = %+d\n", product, product);
}

int Add (int x, int y) {
    return x + y;
}

long long Booth (int multiplicand, int multiplier) {
    int i;
    long long product;
    long long productLH;
    long long productRH;
    int productLHI;
    int productRHI;
    int cOut;
    int negMultiplicand;
    negMultiplicand = Add (~multiplicand, 1);
    product = (long long) Add (0, multiplier);

    for (i = 0; i < 32; i++) {
        if (((product & 1) == 1) && (cOut == 0)) {
            //Mask left half and right half of product
            productLH = (product & 0xFFFFFFFF00000000);
            productRH = (product & 0x00000000FFFFFFFF);

            //Bit shift product so all values are in lower 32 bits
            productLH = (productLH >> 32);

            //Convert left halves and right halves to ints
            productLHI = (int) (productLH & 0x00000000FFFFFFFF);
            productRHI = (int) productRH & (0x00000000FFFFFFFF);
            productLHI = Add(productLHI, negMultiplicand);

            //Put halves back together
            product = (long long) Add(productLHI, 0);
            product = ((product << 32) & 0xFFFFFFFFFFFFFFFF);
            product = (long long) Add((int)product, productRHI);
        }   
        else if (((product & 1) == 0) && (cOut == 1)) {
            //Mask left half and right half of product
            productLH = (product & 0xFFFFFFFF00000000);
            productRH = (product & 0x00000000FFFFFFFF);

            //Bit shift product so all values are in lower 32 bits
            productLH = (productLH >> 32);

            //Convert left halves and right halves to ints
            productLHI = (int) (productLH & 0x00000000FFFFFFFF);
            productRHI = (int) productRH & (0x00000000FFFFFFFF);
            productLHI = Add(productLHI, multiplicand);

            //Put halves back together
            product = (long long) Add(productLHI, 0);
            product = ((product << 32) & 0xFFFFFFFFFFFFFFFF);
            product = (long long) Add((int)product, productRHI);
        }
        cOut = (product & 1);
        product = product >> 1;
    }
    return product;
}

Answer 1

函数 Add() 的返回值可能不是整数类型，但您返回的是 int 类型。如果我们将两个整数相加可能会得到多个 int 类型。