java.math.BigIn teger

[shana07]

I don't understand about this program is doing. Could someone please tell me what it is about. Because I have gcd function in one program that calls this function. Thanks a lot

 
switch (opcode) {
case GCD:       out = b1.gcd(b2).toString();
                            break;

/**
     * Returns a BigInteger whose value is the greatest common divisor of
     * <tt>abs(this)</tt> and <tt>abs(val)</tt>.  Returns 0 if
     * <tt>this==0 &amp;&amp; val==0</tt>.
     *
     * @param  val value with with the GCD is to be computed.
     * @return <tt>GCD(abs(this), abs(val))</tt>
     */
    public BigInteger gcd(BigInteger val) {
        if (val.signum == 0)
        return this.abs();
    else if (this.signum == 0)
        return val.abs();
 
        MutableBigInteger a = new MutableBigInteger(this);
        MutableBigInteger b = new MutableBigInteger(val);
 
        MutableBigInteger result = a.hybridGCD(b);
 
        return new BigInteger(result, 1);
    }

[shana07]

Did you set up the directory structure correctly?

I think yes, because I just paste the two classes in that directory.
So in the src\jonelo\suga r\math directory contains classes:

GeneralMath
MutableBigInteg erMutant
BigIntMutant

What else should be done you think...

[r035198x]

I think yes, because I just paste the two classes in that directory.
So in the src\jonelo\suga r\math directory contains classes:

GeneralMath
MutableBigInteg erMutant
BigIntMutant

What else should be done you think...

and you put the package name correctly in the classes in the package statement.

[shana07]

and you put the package name correctly in the classes in the package statement.

Hurm, I need to consult you about this naming directory/package which I am not clear about it. I have located my program such this:

D:\Assignments\ GOOD\BigAl\BigA l\bigal-src\
inside there contains:
jonelo\bigal\ * 3 classes: Main, Algorithm, BigAlException
jonelo\sugar\ma th\ * classes: GeneralMath, BigIntMutant, MutableBigInteg erMutant
jonelo\sugar\ut il\ *1 class: General

So, from where should I put import statement in Main class?
This is my import statements in Main class, please correct if I made wrong

package jonelo.bigal;

import java.io.*;
import java.math.BigIn teger;
import java.math.BigDe cimal;

import jonelo.sugar.ma th.GeneralMath;
import jonelo.sugar.ma th.BigIntMutant ;
import jonelo.sugar.ma th.MutableBigIn tegerMutant;

[r035198x]

Hurm, I need to consult you about this naming directory/package which I am not clear about it. I have located my program such this:

D:\Assignments\ GOOD\BigAl\BigA l\bigal-src\
inside there contains:
jonelo\bigal\ * 3 classes: Main, Algorithm, BigAlException
jonelo\sugar\ma th\ * classes: GeneralMath, BigIntMutant, MutableBigInteg erMutant
jonelo\sugar\ut il\ *1 class: General

So, from where should I put import statement in Main class?
This is my import statements in Main class, please correct if I made wrong

package jonelo.bigal;

import java.io.*;
import java.math.BigIn teger;
import java.math.BigDe cimal;

import jonelo.sugar.ma th.GeneralMath;
import jonelo.sugar.ma th.BigIntMutant ;
import jonelo.sugar.ma th.MutableBigIn tegerMutant;

Why don't you try to put all your classes in one package first.

[shana07]

Why don't you try to put all your classes in one package first.

This porblem is solved. I created one package like javah/math/BigInteger.
Then I used netbeans to build and run.
About this, i need to ask you: build in netbeans is same as compile?
Then I can see there is one jar created with same program name and build folder?....What happened was, I used prompt before to compile them one by one.

One more thing, what is this statement means?

 int k = (s1 < s2) ? s1 : s2;

[r035198x]

This porblem is solved. I created one package like javah/math/BigInteger.
Then I used netbeans to build and run.
About this, i need to ask you: build in netbeans is same as compile?
Then I can see there is one jar created with same program name and build folder?....What happened was, I used prompt before to compile them one by one.

One more thing, what is this statement means?

 int k = (s1 < s2) ? s1 : s2;

It's a short cut way of writing the if-else construct. Play around with it and you will understand it better then.

[shana07]

Again about java/math package ...
1. I do need help to understand what is this program for.
2. In what situation then it calls binaryGCD (different binaryGCD & hybridGCD)
please..thanks

 /**
     * Calculate GCD of this and b. This and b are changed by the computation.
     */
    MutableBigInteger hybridGCD(MutableBigInteger b)      {
        // Use Euclid's algorithm until the numbers are approximately the
        // same length, then use the binary GCD algorithm to find the GCD.
        MutableBigInteger a = this;
        MutableBigInteger q = new MutableBigInteger(),
                          r = new MutableBigInteger();
 
        while (b.intLen != 0) 
        {
            if (Math.abs(a.intLen - b.intLen) < 2)
                return a.binaryGCD(b);
            a.divide(b, q, r);
            MutableBigInteger swapper = a;
            a = b; b = r; r = swapper;
        }
        return a;
    }

[r035198x]

Again about java/math package ...
1. I do need help to understand what is this program for.
2. In what situation then it calls binaryGCD (different binaryGCD & hybridGCD)
please..thanks

 /**
* Calculate GCD of this and b. This and b are changed by the computation.
*/
MutableBigInteger hybridGCD(MutableBigInteger b) {
// Use Euclid's algorithm until the numbers are approximately the
// same length, then use the binary GCD algorithm to find the GCD.
MutableBigInteger a = this;
MutableBigInteger q = new MutableBigInteger(),
r = new MutableBigInteger();
 
 while (b.intLen != 0) 
 {
 if (Math.abs(a.intLen - b.intLen) < 2)
 return a.binaryGCD(b);
a.divide(b, q, r);
MutableBigInteger swapper = a;
a = b; b = r; r = swapper;
}
return a;
}

What it's used for can be anything where one fells they need the gcd and when it calls which method is actually explained by the comment there :

// Use Euclid's algorithm until the numbers are approximately the
// same length, then use the binary GCD algorithm to find the GCD.

[shana07]

What it's used for can be anything where one fells they need the gcd and when it calls which method is actually explained by the comment there :

// Use Euclid's algorithm until the numbers are approximately the
// same length, then use the binary GCD algorithm to find the GCD.

meaning to say, if I need to write one calculation program to test :
45.gcd(5) or gcd (45, 5) >>> it will call hybrid function and binary both?
Sorry, I need to paste long codes here to show my query .....thanks

while (b.intLen != 0) 
        {
            if (Math.abs(a.intLen - b.intLen) < 2)
                return a.binaryGCD(b);
            a.divide(b, q, r);
            MutableBigInteger swapper = a;
            a = b; b = r; r = swapper;
        }
        return a;
    }
 
 
    /**
     * Calculate GCD of this and v.
     * Assumes that this and v are not zero.
     */
    private MutableBigInteger binaryGCD(MutableBigInteger v)      {
        // Algorithm B from Knuth section 4.5.2
        MutableBigInteger u = this;
        MutableBigInteger q = new MutableBigInteger(),
            r = new MutableBigInteger();
 
        // step B1
        int s1 = u.getLowestSetBit();
        int s2 = v.getLowestSetBit();
        int k = (s1 < s2) ? s1 : s2;  //
        if (k != 0) {
            u.rightShift(k);
            v.rightShift(k);
        }
 
        // step B2
        boolean uOdd = (k==s1);
        MutableBigInteger t = uOdd ? v: u;
        int tsign = uOdd ? -1 : 1;
 
        int lb;
        while ((lb = t.getLowestSetBit()) >= 0) {
            // steps B3 and B4
            t.rightShift(lb);
            // step B5
            if (tsign > 0)
                u = t;
            else
                v = t;
 
            // Special case one word numbers
            if (u.intLen < 2 && v.intLen < 2) {
                int x = u.value[u.offset];
                int y = v.value[v.offset];
                x  = binaryGcd(x, y);
                r.value[0] = x;
                r.intLen = 1;
                r.offset = 0;
                if (k > 0)
                    r.leftShift(k);
                return r;
            }
 
            // step B6
            if ((tsign = u.difference(v)) == 0)
                break;
            t = (tsign >= 0) ? u : v;
        }
 
        if (k > 0)
            u.leftShift(k);
        return u;
    }
 
    /**
     * Calculate GCD of a and b interpreted as unsigned integers.
     */
    static int binaryGcd(int a, int b) {
        if (b==0)
            return a;
        if (a==0)
            return b;
 
        int x;
        int aZeros = 0;
        while ((x = (int)a & 0xff) == 0) {
            a >>>= 8;
            aZeros += 8;
        }
        int y = BigInteger.trailingZeroTable[x];
        aZeros += y;
        a >>>= y;
 
        int bZeros = 0;
        while ((x = (int)b & 0xff) == 0) {
            b >>>= 8;
            bZeros += 8;
        }
        y = BigInteger.trailingZeroTable[x];
        bZeros += y;
        b >>>= y;
 
        int t = (aZeros < bZeros ? aZeros : bZeros);
 
        while (a != b) {
            if ((a+0x80000000) > (b+0x80000000)) {  // a > b as unsigned
                a -= b;
 
                while ((x = (int)a & 0xff) == 0)
                    a >>>= 8;
                a >>>= BigInteger.trailingZeroTable[x];
            } else {
                b -= a;
 
                while ((x = (int)b & 0xff) == 0)
                    b >>>= 8;
                b >>>= BigInteger.trailingZeroTable[x];
            }
        }
        return a<<t;
    }

[shana07]

Need help, If someone has experience in core java class - MutableBigInteg er, please share some with me. BinaryGCD here is what for...Let say I have gcd(45, 5) is that involves with binaryGCD(Mutab leBigInteger v)) too?
Thankss