java.math.BigInteger

[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);
    }

[r035198x]

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);
}

which part specifically do you not understand?

[shana07]

which part specifically do you not understand?

The java package code. From my reading, signum is either '+', '-' or 0.
Then, mutableBigInteger is for what?
As for gcd (a, b) calculation actually is about
a.gcd(b)
Then it involves with operator 'mod' to get remainder.
Where can I check those operators?

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);
}

[r035198x]

The java package code. From my reading, signum is either '+', '-' or 0.
Then, mutableBigInteger is for what?
As for gcd (a, b) calculation actually is about
a.gcd(b)
Then it involves with operator 'mod' to get remainder.
Where can I check those operators?

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);
}

MutableBigInteger is another class in the java.math package. It's implementation of hybridGCD is

 
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;
    }
 

[shana07]

MutableBigInteger is another class in the java.math package. It's implementation of hybridGCD is

 
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;
    }
 

Oh it's there...alright. TQ
One more question I need to consult you.Is it possible for me to replace any operators inside this class (only gcd subroutines)? Seems I can't do mutation on my program (that calls gcd class) .
* Aim - to do mutation to this gcd function. Because I remember last time, I tried on other java default pakcages and from netbean I can't open that package anymore once I changed it (unzipped the packages and zipped back).....sorry If this confusing you....

[r035198x]

Oh it's there...alright. TQ
One more question I need to consult you.Is it possible for me to replace any operators inside this class (only gcd subroutines)? Seems I can't do mutation on my program (that calls gcd class) .
* Aim - to do mutation to this gcd function. Because I remember last time, I tried on other java default pakcages and from netbean I can't open that package anymore once I changed it (unzipped the packages and zipped back).....sorry If this confusing you....

Do not change any classes in your java directories.
If you need to use any of them, copy them somewhere else and edit them there if you need to.

[shana07]

Do not change any classes in your java directories.
If you need to use any of them, copy them somewhere else and edit them there if you need to.

Meaning to say that this is possible for me to do so isn't.
I need your advice regarding this please..
1. I have copied those two default java classes in my program under test
2. I renamed classes names as below:

java.math.BigInteger >>> jonelo.sugar.math.MutableBigIntegerMutant
java.math.MutableBigInteger >>> jonelo.sugar.math.BigIntMutant

3. And I have renamed all methods/variables/constructors with BigIntMutant
and MutableBigIntegerMutant

4. Is that possible for me to ask my program to refer to these two new classes when it calls gcd (I changed gcd method >>> gcdMutant).

case GCD:       out = b1.gcdMutant(b2).toString();
                            break;

When I compile my main program - these 3 errors occured, Please advise what should I do..thank you

Main.java:31: cannot find symbol
symbol : class BigIntMutant
location: package jonelo.sugar.math
import jonelo.sugar.math.BigIntMutant;
^
Main.java:32: cannot find symbol
symbol : class MutableBigIntegerMutant
location: package jonelo.sugar.math
import jonelo.sugar.math.MutableBigIntegerMutant;
^
Main.java:528: cannot find symbol
symbol : method gcdMutant(java.math.BigInteger)
location: class java.math.BigInteger
case GCD: out = b1.gcdMutant(b2).toString();
^
3 errors

[r035198x]

Meaning to say that this is possible for me to do so isn't.
I need your advice regarding this please..
1. I have copied those two default java classes in my program under test
2. I renamed classes names as below:

java.math.BigInteger >>> jonelo.sugar.math.MutableBigIntegerMutant
java.math.MutableBigInteger >>> jonelo.sugar.math.BigIntMutant

3. And I have renamed all methods/variables/constructors with BigIntMutant
and MutableBigIntegerMutant

4. Is that possible for me to ask my program to refer to these two new classes when it calls gcd (I changed gcd method >>> gcdMutant).

case GCD: out = b1.gcdMutant(b2).toString();
break;

When I compile my main program - these 3 errors occured, Please advise what should I do..thank you

Main.java:31: cannot find symbol
symbol : class BigIntMutant
location: package jonelo.sugar.math
import jonelo.sugar.math.BigIntMutant;
^
Main.java:32: cannot find symbol
symbol : class MutableBigIntegerMutant
location: package jonelo.sugar.math
import jonelo.sugar.math.MutableBigIntegerMutant;
^
Main.java:528: cannot find symbol
symbol : method gcdMutant(java.math.BigInteger)
location: class java.math.BigInteger
case GCD: out = b1.gcdMutant(b2).toString();
^
3 errors

First you will need to make sure that the classes you copied are not referencing other classes that you may not have copied.
Then you need to make sure that your import statements are correct e.g you cannot import a class that you are actually writting code for.

[shana07]

First you will need to make sure that the classes you copied are not referencing other classes that you may not have copied.
Then you need to make sure that your import statements are correct e.g you cannot import a class that you are actually writting code for.

good example. Help me take a look at this import of the Main class. Why when I compile the Main class comes that errors: can't find class from that import statement....

package jonelo.bigal;
import java.io.*;
import java.math.BigInteger;
import java.math.BigDecimal;
import jonelo.sugar.math.GeneralMath; // ** Check: This default class from this program
 
import jonelo.sugar.math.BigIntMutant; //** Check: That's why I put these altered class in here
import jonelo.sugar.math.MutableBigIntegerMutant; //** Check: same as this
 

[r035198x]

good example. Help me take a look at this import of the Main class. Why when I compile the Main class comes that errors: can't find class from that import statement....

package jonelo.bigal;
import java.io.*;
import java.math.BigInteger;
import java.math.BigDecimal;
import jonelo.sugar.math.GeneralMath; // ** Check: This default class from this program
 
import jonelo.sugar.math.BigIntMutant; //** Check: That's why I put these altered class in here
import jonelo.sugar.math.MutableBigIntegerMutant; //** Check: same as this
 

Did you set up the directory structure correctly?

[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\sugar\math directory contains classes:

GeneralMath
MutableBigIntegerMutant
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\sugar\math directory contains classes:

GeneralMath
MutableBigIntegerMutant
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\BigAl\bigal-src\
inside there contains:
jonelo\bigal\ * 3 classes: Main, Algorithm, BigAlException
jonelo\sugar\math\ * classes: GeneralMath, BigIntMutant, MutableBigIntegerMutant
jonelo\sugar\util\ *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.BigInteger;
import java.math.BigDecimal;

import jonelo.sugar.math.GeneralMath;
import jonelo.sugar.math.BigIntMutant;
import jonelo.sugar.math.MutableBigIntegerMutant;

[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\BigAl\bigal-src\
inside there contains:
jonelo\bigal\ * 3 classes: Main, Algorithm, BigAlException
jonelo\sugar\math\ * classes: GeneralMath, BigIntMutant, MutableBigIntegerMutant
jonelo\sugar\util\ *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.BigInteger;
import java.math.BigDecimal;

import jonelo.sugar.math.GeneralMath;
import jonelo.sugar.math.BigIntMutant;
import jonelo.sugar.math.MutableBigIntegerMutant;

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 - MutableBigInteger, please share some with me. BinaryGCD here is what for...Let say I have gcd(45, 5) is that involves with binaryGCD(MutableBigInteger v)) too?
Thankss