Booth的算法是一种乘法算法，将两个有符号的二进制数乘以2的恭维表示法。
Booth使用的台式计算器在班次上比添加时要快，并创建了算法来提高速度。 Booth的算法在计算机体系结构的研究中很有用。这是算法的实现。
例子：
Input : 0110, 0010
Output : qn q[n+1] AC QR sc(step count)
initial 0000 0010 4
0 0 rightShift 0000 0001 3
1 0 A = A - BR 1010
rightShift 1101 0000 2
0 1 A = A + BR 0011
rightShift 0001 1000 1
0 0 rightShift 0000 1100 0
Result=1100
算法 ：
Put multiplicand in BR and multiplier in QR
and then the algorithm works as per the following conditions :
1. If Qn and Qn+1 are same i.e. 00 or 11 perform arithematic shift by 1 bit.
2. If Qn Qn+1 = 10 do A= A + BR and perform arithematic shift by 1 bit.
3. If Qn Qn+1 = 01 do A= A – BR and perform arithematic shift by 1 bit.
C++
// CPP code to implement booth's algorithm
#include
using namespace std;
// function to perform adding in the accumulator
void add(int ac[], int x[], int qrn)
{
int i, c = 0;
for (i = 0; i < qrn; i++) {
// updating accumulator with A = A + BR
ac[i] = ac[i] + x[i] + c;
if (ac[i] > 1) {
ac[i] = ac[i] % 2;
c = 1;
}
else
c = 0;
}
}
// function to find the number's complement
void complement(int a[], int n)
{
int i;
int x[8] = { 0};
x[0] = 1;
for (i = 0; i < n; i++) {
a[i] = (a[i] + 1) % 2;
}
add(a, x, n);
}
// function ro perform right shift
void rightShift(int ac[], int qr[], int& qn, int qrn)
{
int temp, i;
temp = ac[0];
qn = qr[0];
cout << "\t\trightShift\t";
for (i = 0; i < qrn - 1; i++) {
ac[i] = ac[i + 1];
qr[i] = qr[i + 1];
}
qr[qrn - 1] = temp;
}
// function to display oprations
void display(int ac[], int qr[], int qrn)
{
int i;
// accumulator content
for (i = qrn - 1; i >= 0; i--)
cout << ac[i];
cout << "\t";
// multiplier content
for (i = qrn - 1; i >= 0; i--)
cout << qr[i];
}
// Function to implement booth's algo
void boothAlgorithm(int br[], int qr[], int mt[], int qrn, int sc)
{
int qn = 0, ac[10] = { 0 };
int temp = 0;
cout << "qn\tq[n+1]\t\tBR\t\tAC\tQR\t\tsc\n";
cout << "\t\t\tinitial\t\t";
display(ac, qr, qrn);
cout << "\t\t" << sc << "\n";
while (sc != 0) {
cout << qr[0] << "\t" << qn;
// SECOND CONDITION
if ((qn + qr[0]) == 1)
{
if (temp == 0) {
// subtract BR from accumulator
add(ac, mt, qrn);
cout << "\t\tA = A - BR\t";
for (int i = qrn - 1; i >= 0; i--)
cout << ac[i];
temp = 1;
}
// THIRD CONDITION
else if (temp == 1)
{
// add BR to accumulator
add(ac, br, qrn);
cout << "\t\tA = A + BR\t";
for (int i = qrn - 1; i >= 0; i--)
cout << ac[i];
temp = 0;
}
cout << "\n\t";
rightShift(ac, qr, qn, qrn);
}
// FIRST CONDITION
else if (qn - qr[0] == 0)
rightShift(ac, qr, qn, qrn);
display(ac, qr, qrn);
cout << "\t";
// decrement counter
sc--;
cout << "\t" << sc << "\n";
}
}
// driver code
int main(int argc, char** arg)
{
int mt[10], sc;
int brn, qrn;
// Number of multiplicand bit
brn = 4;
// multiplicand
int br[] = { 0, 1, 1, 0 };
// copy multiplier to temp array mt[]
for (int i = brn - 1; i >= 0; i--)
mt[i] = br[i];
reverse(br, br + brn);
complement(mt, brn);
// No. of multiplier bit
qrn = 4;
// sequence counter
sc = qrn;
// multiplier
int qr[] = { 1, 0, 1, 0 };
reverse(qr, qr + qrn);
boothAlgorithm(br, qr, mt, qrn, sc);
cout << endl
<< "Result = ";
for (int i = qrn - 1; i >= 0; i--)
cout << qr[i];
} Java
// Java code to implement booth's algorithm
class GFG
{
// function to perform adding in the accumulator
static void add(int ac[], int x[], int qrn)
{
int i, c = 0;
for (i = 0; i < qrn; i++)
{
// updating accumulator with A = A + BR
ac[i] = ac[i] + x[i] + c;
if (ac[i] > 1)
{
ac[i] = ac[i] % 2;
c = 1;
}
else
{
c = 0;
}
}
}
// function to find the number's complement
static void complement(int a[], int n)
{
int i;
int[] x = new int[8];
x[0] = 1;
for (i = 0; i < n; i++)
{
a[i] = (a[i] + 1) % 2;
}
add(a, x, n);
}
// function ro perform right shift
static void rightShift(int ac[], int qr[],
int qn, int qrn)
{
int temp, i;
temp = ac[0];
qn = qr[0];
System.out.print("\t\trightShift\t");
for (i = 0; i < qrn - 1; i++)
{
ac[i] = ac[i + 1];
qr[i] = qr[i + 1];
}
qr[qrn - 1] = temp;
}
// function to display oprations
static void display(int ac[], int qr[], int qrn)
{
int i;
// accumulator content
for (i = qrn - 1; i >= 0; i--)
{
System.out.print(ac[i]);
}
System.out.print("\t");
// multiplier content
for (i = qrn - 1; i >= 0; i--)
{
System.out.print(qr[i]);
}
}
// Function to implement booth's algo
static void boothAlgorithm(int br[], int qr[], int mt[],
int qrn, int sc)
{
int qn = 0;
int[] ac = new int[10];
int temp = 0;
System.out.print("qn\tq[n+1]\t\tBR\t\tAC\tQR\t\tsc\n");
System.out.print("\t\t\tinitial\t\t");
display(ac, qr, qrn);
System.out.print("\t\t" + sc + "\n");
while (sc != 0)
{
System.out.print(qr[0] + "\t" + qn);
// SECOND CONDITION
if ((qn + qr[0]) == 1)
{
if (temp == 0)
{
// subtract BR from accumulator
add(ac, mt, qrn);
System.out.print("\t\tA = A - BR\t");
for (int i = qrn - 1; i >= 0; i--)
{
System.out.print(ac[i]);
}
temp = 1;
}
// THIRD CONDITION
else if (temp == 1)
{
// add BR to accumulator
add(ac, br, qrn);
System.out.print("\t\tA = A + BR\t");
for (int i = qrn - 1; i >= 0; i--)
{
System.out.print(ac[i]);
}
temp = 0;
}
System.out.print("\n\t");
rightShift(ac, qr, qn, qrn);
}
// FIRST CONDITION
else if (qn - qr[0] == 0)
{
rightShift(ac, qr, qn, qrn);
}
display(ac, qr, qrn);
System.out.print("\t");
// decrement counter
sc--;
System.out.print("\t" + sc + "\n");
}
}
static void reverse(int a[])
{
int i, k, n = a.length;
int t;
for (i = 0; i < n / 2; i++)
{
t = a[i];
a[i] = a[n - i - 1];
a[n - i - 1] = t;
}
}
// Driver code
public static void main(String[] args)
{
int[] mt = new int[10];
int sc;
int brn, qrn;
// Number of multiplicand bit
brn = 4;
// multiplicand
int br[] = {0, 1, 1, 0};
// copy multiplier to temp array mt[]
for (int i = brn - 1; i >= 0; i--)
{
mt[i] = br[i];
}
reverse(br);
complement(mt, brn);
// No. of multiplier bit
qrn = 4;
// sequence counter
sc = qrn;
// multiplier
int qr[] = {1, 0, 1, 0};
reverse(qr);
boothAlgorithm(br, qr, mt, qrn, sc);
System.out.print("\n"
+ "Result = ");
for (int i = qrn - 1; i >= 0; i--)
{
System.out.print(qr[i]);
}
}
}
/* This code contributed by PrinciRaj1992 */C#
// C# code to implement
// booth's algorithm
using System;
class GFG
{
// function to perform
// adding in the accumulator
static void add(int []ac,
int []x,
int qrn)
{
int i, c = 0;
for (i = 0; i < qrn; i++)
{
// updating accumulator
// with A = A + BR
ac[i] = ac[i] + x[i] + c;
if (ac[i] > 1)
{
ac[i] = ac[i] % 2;
c = 1;
}
else
c = 0;
}
}
// function to find
// the number's complement
static void complement(int []a, int n)
{
int i;
int []x = new int[8];
Array.Clear(x, 0, 8);
x[0] = 1;
for (i = 0; i < n; i++)
{
a[i] = (a[i] + 1) % 2;
}
add(a, x, n);
}
// function to perform
// right shift
static void rightShift(int []ac, int []qr,
ref int qn, int qrn)
{
int temp, i;
temp = ac[0];
qn = qr[0];
Console.Write("\t\trightShift\t");
for (i = 0; i < qrn - 1; i++)
{
ac[i] = ac[i + 1];
qr[i] = qr[i + 1];
}
qr[qrn - 1] = temp;
}
// function to display
// operations
static void display(int []ac,
int []qr,
int qrn)
{
int i;
// accumulator content
for (i = qrn - 1; i >= 0; i--)
Console.Write(ac[i]);
Console.Write("\t");
// multiplier content
for (i = qrn - 1; i >= 0; i--)
Console.Write(qr[i]);
}
// Function to implement
// booth's algo
static void boothAlgorithm(int []br, int []qr,
int []mt, int qrn,
int sc)
{
int qn = 0;
int []ac = new int[10];
Array.Clear(ac, 0, 10);
int temp = 0;
Console.Write("qn\tq[n + 1]\tBR\t" +
"\tAC\tQR\t\tsc\n");
Console.Write("\t\t\tinitial\t\t");
display(ac, qr, qrn);
Console.Write("\t\t" + sc + "\n");
while (sc != 0)
{
Console.Write(qr[0] + "\t" + qn);
// SECOND CONDITION
if ((qn + qr[0]) == 1)
{
if (temp == 0)
{
// subtract BR
// from accumulator
add(ac, mt, qrn);
Console.Write("\t\tA = A - BR\t");
for (int i = qrn - 1; i >= 0; i--)
Console.Write(ac[i]);
temp = 1;
}
// THIRD CONDITION
else if (temp == 1)
{
// add BR to accumulator
add(ac, br, qrn);
Console.Write("\t\tA = A + BR\t");
for (int i = qrn - 1; i >= 0; i--)
Console.Write(ac[i]);
temp = 0;
}
Console.Write("\n\t");
rightShift(ac, qr, ref qn, qrn);
}
// FIRST CONDITION
else if (qn - qr[0] == 0)
rightShift(ac, qr,
ref qn, qrn);
display(ac, qr, qrn);
Console.Write("\t");
// decrement counter
sc--;
Console.Write("\t" + sc + "\n");
}
}
// Driver code
static void Main()
{
int []mt = new int[10];
int sc, brn, qrn;
// Number of
// multiplicand bit
brn = 4;
// multiplicand
int []br = new int[]{ 0, 1, 1, 0 };
// copy multiplier
// to temp array mt[]
for (int i = brn - 1; i >= 0; i--)
mt[i] = br[i];
Array.Reverse(br);
complement(mt, brn);
// No. of
// multiplier bit
qrn = 4;
// sequence
// counter
sc = qrn;
// multiplier
int []qr = new int[]{ 1, 0, 1, 0 };
Array.Reverse(qr);
boothAlgorithm(br, qr,
mt, qrn, sc);
Console.WriteLine();
Console.Write("Result = ");
for (int i = qrn - 1; i >= 0; i--)
Console.Write(qr[i]);
}
}
// This code is contributed by
// Manish Shaw(manishshaw1)输出 ：
qn q[n + 1] BR AC QR sc
initial 0000 1010 4
0 0 rightShift 0000 0101 3
1 0 A = A - BR 1010
rightShift 1101 0010 2
0 1 A = A + BR 0011
rightShift 0001 1001 1
1 0 A = A - BR 1011
rightShift 1101 1100 0
Result = 1100