IntegerFunctions (Bouncy Castle Cryptography 1.71 API Specification)

java.lang.Object
- org.bouncycastle.pqc.math.linearalgebra.IntegerFunctions

```
public final class IntegerFunctions
extends java.lang.Object
```
Class of number-theory related functions for use with integers represented as int's or BigInteger objects.

Method Summary

All Methods Static Methods Concrete Methods Deprecated Methods
Modifier and Type	Method and Description
`static java.math.BigInteger`	`binomial(int n, int t)` Computes the binomial coefficient (n\|t) ("n over t").
`static int`	`bitCount(int a)`
`static int`	`ceilLog(java.math.BigInteger a)` Compute the smallest integer that is greater than or equal to the logarithm to the base 2 of the given BigInteger.
`static int`	`ceilLog(int a)` Compute the smallest integer that is greater than or equal to the logarithm to the base 2 of the given integer.
`static int`	`ceilLog256(int n)` Compute ceil(log_256 n), the number of bytes needed to encode the integer n.
`static int`	`ceilLog256(long n)` Compute ceil(log_256 n), the number of bytes needed to encode the long integer n.
`static java.math.BigInteger[]`	`divideAndRound(java.math.BigInteger[] a, java.math.BigInteger b)`
`static java.math.BigInteger`	`divideAndRound(java.math.BigInteger a, java.math.BigInteger b)`
`static java.math.BigInteger[]`	`extgcd(java.math.BigInteger a, java.math.BigInteger b)` Extended euclidian algorithm (computes gcd and representation).
`static int[]`	`extGCD(int a, int b)` Extended euclidian algorithm (computes gcd and representation).
`static float`	`floatPow(float f, int i)` int power of a base float, only use for small ints
`static int`	`floorLog(java.math.BigInteger a)` Compute the integer part of the logarithm to the base 2 of the given integer.
`static int`	`floorLog(int a)` Compute the integer part of the logarithm to the base 2 of the given integer.
`static int`	`gcd(int u, int v)` Computes the greatest common divisor of the two specified integers
`static byte[]`	`integerToOctets(java.math.BigInteger val)`
`static float`	`intRoot(int base, int root)` Takes an approximation of the root from an integer base, using newton's algorithm
`static boolean`	`isIncreasing(int[] a)`
`static int`	`isPower(int a, int p)` Tests whether an integer a is power of another integer p.
`static boolean`	`isPrime(int n)` Miller-Rabin-Test, determines wether the given integer is probably prime or composite.
`static int`	`jacobi(java.math.BigInteger A, java.math.BigInteger B)` Computes the value of the Jacobi symbol (A\|B).
`static java.math.BigInteger`	`leastCommonMultiple(java.math.BigInteger[] numbers)` Computation of the least common multiple of a set of BigIntegers.
`static int`	`leastDiv(int a)` Find and return the least non-trivial divisor of an integer a.
`static double`	`log(double x)` Deprecated. use MathFunctions.log(double) instead
`static double`	`log(long x)` Deprecated. use MathFunctions.log(long) instead
`static int`	`maxPower(int a)` Compute the largest h with 2^h \| a if a!=0.
`static long`	`mod(long a, long m)` Returns a long integer whose value is (a mod m).
`static int`	`modInverse(int a, int mod)` Computes the modular inverse of an integer a
`static long`	`modInverse(long a, long mod)` Computes the modular inverse of an integer a
`static int`	`modPow(int a, int e, int n)` Compute a e mod n.
`static java.math.BigInteger`	`nextPrime(long n)` Computes the next prime greater than n.
`static java.math.BigInteger`	`nextProbablePrime(java.math.BigInteger n)` Compute the next probable prime greater than n with the default certainty (20).
`static java.math.BigInteger`	`nextProbablePrime(java.math.BigInteger n, int certainty)` Compute the next probable prime greater than n with the specified certainty.
`static int`	`nextSmallerPrime(int n)` Returns the largest prime smaller than the given integer
`static java.math.BigInteger`	`octetsToInteger(byte[] data)`
`static java.math.BigInteger`	`octetsToInteger(byte[] data, int offset, int length)`
`static int`	`order(int g, int p)` determines the order of g modulo p, p prime and 1 < g < p.
`static boolean`	`passesSmallPrimeTest(java.math.BigInteger candidate)` Short trial-division test to find out whether a number is not prime.
`static int`	`pow(int a, int e)` Compute a e.
`static long`	`pow(long a, int e)` Compute a e.
`static java.math.BigInteger`	`randomize(java.math.BigInteger upperBound)`
`static java.math.BigInteger`	`randomize(java.math.BigInteger upperBound, java.security.SecureRandom prng)`
`static java.math.BigInteger`	`reduceInto(java.math.BigInteger n, java.math.BigInteger begin, java.math.BigInteger end)` Reduces an integer into a given interval
`static java.math.BigInteger`	`squareRoot(java.math.BigInteger a)` Extract the truncated square root of a BigInteger.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - jacobi
```
public static int jacobi(java.math.BigInteger A,
                         java.math.BigInteger B)
```
    Computes the value of the Jacobi symbol (A|B). The following properties hold for the Jacobi symbol which makes it a very efficient way to evaluate the Legendre symbol
    (A|B) = 0 IF gcd(A,B) > 1 (-1|B) = 1 IF n = 1 (mod 1) (-1|B) = -1 IF n = 3 (mod 4) (A|B) (C|B) = (AC|B) (A|B) (A|C) = (A|CB) (A|B) = (C|B) IF A = C (mod B) (2|B) = 1 IF N = 1 OR 7 (mod 8) (2|B) = 1 IF N = 3 OR 5 (mod 8)
    
    Parameters:
    
    A - integer value
    
    B - integer value
    
    Returns:
    
    value of the jacobi symbol (A|B)
  - gcd
```
public static int gcd(int u,
                      int v)
```
    Computes the greatest common divisor of the two specified integers
    
    Parameters:
    
    u - - first integer
    
    v - - second integer
    
    Returns:
    
    gcd(a, b)
  - extGCD
```
public static int[] extGCD(int a,
                           int b)
```
    Extended euclidian algorithm (computes gcd and representation).
    
    Parameters:
    
    a - the first integer
    
    b - the second integer
    
    Returns:
    
    (g,u,v), where g = gcd(abs(a),abs(b)) = ua + vb
  - divideAndRound
```
public static java.math.BigInteger divideAndRound(java.math.BigInteger a,
                                                  java.math.BigInteger b)
```
  - divideAndRound
```
public static java.math.BigInteger[] divideAndRound(java.math.BigInteger[] a,
                                                    java.math.BigInteger b)
```
  - ceilLog
```
public static int ceilLog(java.math.BigInteger a)
```
    Compute the smallest integer that is greater than or equal to the logarithm to the base 2 of the given BigInteger.
    
    Parameters:
    
    a - the integer
    
    Returns:
    
    ceil[log(a)]
  - ceilLog
```
public static int ceilLog(int a)
```
    Compute the smallest integer that is greater than or equal to the logarithm to the base 2 of the given integer.
    
    Parameters:
    
    a - the integer
    
    Returns:
    
    ceil[log(a)]
  - ceilLog256
```
public static int ceilLog256(int n)
```
    Compute ceil(log_256 n), the number of bytes needed to encode the integer n.
    
    Parameters:
    
    n - the integer
    
    Returns:
    
    the number of bytes needed to encode n
  - ceilLog256
```
public static int ceilLog256(long n)
```
    Compute ceil(log_256 n), the number of bytes needed to encode the long integer n.
    
    Parameters:
    
    n - the long integer
    
    Returns:
    
    the number of bytes needed to encode n
  - floorLog
```
public static int floorLog(java.math.BigInteger a)
```
    Compute the integer part of the logarithm to the base 2 of the given integer.
    
    Parameters:
    
    a - the integer
    
    Returns:
    
    floor[log(a)]
  - floorLog
```
public static int floorLog(int a)
```
    Compute the integer part of the logarithm to the base 2 of the given integer.
    
    Parameters:
    
    a - the integer
    
    Returns:
    
    floor[log(a)]
  - maxPower
```
public static int maxPower(int a)
```
    Compute the largest h with 2^h | a if a!=0.
    
    Parameters:
    
    a - an integer
    
    Returns:
    
    the largest h with 2^h | a if a!=0, 0 otherwise
  - bitCount
```
public static int bitCount(int a)
```
    Parameters:
    
    a - an integer
    
    Returns:
    
    the number of ones in the binary representation of an integer a
  - order
```
public static int order(int g,
                        int p)
```
    determines the order of g modulo p, p prime and 1 < g < p. This algorithm is only efficient for small p (see X9.62-1998, p. 68).
    
    Parameters:
    
    g - an integer with 1 < g < p
    
    p - a prime
    
    Returns:
    
    the order k of g (that is k is the smallest integer with g k = 1 mod p
  - reduceInto
```
public static java.math.BigInteger reduceInto(java.math.BigInteger n,
                                              java.math.BigInteger begin,
                                              java.math.BigInteger end)
```
    Reduces an integer into a given interval
    
    Parameters:
    
    n - - the integer
    
    begin - - left bound of the interval
    
    end - - right bound of the interval
    
    Returns:
    
    n reduced into [begin,end]
  - pow
```
public static int pow(int a,
                      int e)
```
    Compute a e.
    
    Parameters:
    
    a - the base
    
    e - the exponent
    
    Returns:
    
    a e
  - pow
```
public static long pow(long a,
                       int e)
```
    Compute a e.
    
    Parameters:
    
    a - the base
    
    e - the exponent
    
    Returns:
    
    a e
  - modPow
```
public static int modPow(int a,
                         int e,
                         int n)
```
    Compute a e mod n.
    
    Parameters:
    
    a - the base
    
    e - the exponent
    
    n - the modulus
    
    Returns:
    
    a e mod n
  - extgcd
```
public static java.math.BigInteger[] extgcd(java.math.BigInteger a,
                                            java.math.BigInteger b)
```
    Extended euclidian algorithm (computes gcd and representation).
    
    Parameters:
    
    a - - the first integer
    
    b - - the second integer
    
    Returns:
    
    (d,u,v), where d = gcd(a,b) = ua + vb
  - leastCommonMultiple
```
public static java.math.BigInteger leastCommonMultiple(java.math.BigInteger[] numbers)
```
    Computation of the least common multiple of a set of BigIntegers.
    
    Parameters:
    
    numbers - - the set of numbers
    
    Returns:
    
    the lcm(numbers)
  - mod
```
public static long mod(long a,
                       long m)
```
    Returns a long integer whose value is (a mod m). This method differs from % in that it always returns a non-negative integer.
    
    Parameters:
    
    a - value on which the modulo operation has to be performed.
    
    m - the modulus.
    
    Returns:
    
    a mod m
  - modInverse
```
public static int modInverse(int a,
                             int mod)
```
    Computes the modular inverse of an integer a
    
    Parameters:
    
    a - - the integer to invert
    
    mod - - the modulus
    
    Returns:
    
    a -1 mod n
  - modInverse
```
public static long modInverse(long a,
                              long mod)
```
    Computes the modular inverse of an integer a
    
    Parameters:
    
    a - - the integer to invert
    
    mod - - the modulus
    
    Returns:
    
    a -1 mod n
  - isPower
```
public static int isPower(int a,
                          int p)
```
    Tests whether an integer a is power of another integer p.
    
    Parameters:
    
    a - - the first integer
    
    p - - the second integer
    
    Returns:
    
    n if a = p^n or -1 otherwise
  - leastDiv
```
public static int leastDiv(int a)
```
    Find and return the least non-trivial divisor of an integer a.
    
    Parameters:
    
    a - - the integer
    
    Returns:
    
    divisor p >1 or 1 if a = -1,0,1
  - isPrime
```
public static boolean isPrime(int n)
```
    Miller-Rabin-Test, determines wether the given integer is probably prime or composite. This method returns true if the given integer is prime with probability 1 - 2 -20.
    
    Parameters:
    
    n - the integer to test for primality
    
    Returns:
    
    true if the given integer is prime with probability 2 -100, false otherwise
  - passesSmallPrimeTest
```
public static boolean passesSmallPrimeTest(java.math.BigInteger candidate)
```
    Short trial-division test to find out whether a number is not prime. This test is usually used before a Miller-Rabin primality test.
    
    Parameters:
    
    candidate - the number to test
    
    Returns:
    
    true if the number has no factor of the tested primes, false if the number is definitely composite
  - nextSmallerPrime
```
public static int nextSmallerPrime(int n)
```
    Returns the largest prime smaller than the given integer
    
    Parameters:
    
    n - - upper bound
    
    Returns:
    
    the largest prime smaller than n, or 1 if n <= 2
  - nextProbablePrime
```
public static java.math.BigInteger nextProbablePrime(java.math.BigInteger n,
                                                     int certainty)
```
    Compute the next probable prime greater than n with the specified certainty.
    
    Parameters:
    
    n - a integer number
    
    certainty - the certainty that the generated number is prime
    
    Returns:
    
    the next prime greater than n
  - nextProbablePrime
```
public static java.math.BigInteger nextProbablePrime(java.math.BigInteger n)
```
    Compute the next probable prime greater than n with the default certainty (20).
    
    Parameters:
    
    n - a integer number
    
    Returns:
    
    the next prime greater than n
  - nextPrime
```
public static java.math.BigInteger nextPrime(long n)
```
    Computes the next prime greater than n.
    
    Parameters:
    
    n - a integer number
    
    Returns:
    
    the next prime greater than n
  - binomial
```
public static java.math.BigInteger binomial(int n,
                                            int t)
```
    Computes the binomial coefficient (n|t) ("n over t"). Formula: if n !=0 and t != 0 then (n|t) = Mult(i=1, t): (n-(i-1))/i

Parameters:: n - - the "upper" integer; t - - the "lower" integer
Returns:: the binomialcoefficient "n over t" as BigInteger

randomize

public static java.math.BigInteger randomize(java.math.BigInteger upperBound)

randomize

public static java.math.BigInteger randomize(java.math.BigInteger upperBound,
                                             java.security.SecureRandom prng)

squareRoot
```
public static java.math.BigInteger squareRoot(java.math.BigInteger a)
```
Extract the truncated square root of a BigInteger.

Parameters:

a - - value out of which we extract the square root

Returns:

the truncated square root of a

intRoot
```
public static float intRoot(int base,
                            int root)
```
Takes an approximation of the root from an integer base, using newton's algorithm

Parameters:

base - the base to take the root from

root - the root, for example 2 for a square root

floatPow
```
public static float floatPow(float f,
                             int i)
```
int power of a base float, only use for small ints

Parameters:

f - base float

i - power to be raised to.

Returns:

int power i of f

log
```
public static double log(double x)
```
Deprecated. use MathFunctions.log(double) instead

calculate the logarithm to the base 2.

Parameters:

x - any double value

Returns:

log_2(x)

log
```
public static double log(long x)
```
Deprecated. use MathFunctions.log(long) instead

calculate the logarithm to the base 2.

Parameters:

x - any long value >=1

Returns:

log_2(x)

isIncreasing

public static boolean isIncreasing(int[] a)

integerToOctets

public static byte[] integerToOctets(java.math.BigInteger val)

octetsToInteger

public static java.math.BigInteger octetsToInteger(byte[] data,
                                                   int offset,
                                                   int length)

octetsToInteger

public static java.math.BigInteger octetsToInteger(byte[] data)

Class IntegerFunctions

Method Summary

Methods inherited from class java.lang.Object

Method Detail

jacobi

gcd

extGCD

divideAndRound

divideAndRound

ceilLog

ceilLog

ceilLog256

ceilLog256

floorLog

floorLog

maxPower

bitCount

order

reduceInto

pow

pow

modPow

extgcd

leastCommonMultiple

mod

modInverse

modInverse

isPower

leastDiv

isPrime

passesSmallPrimeTest

nextSmallerPrime

nextProbablePrime

nextProbablePrime

nextPrime

binomial

randomize

randomize

squareRoot

intRoot

floatPow

log

log

isIncreasing

integerToOctets

octetsToInteger

octetsToInteger