Java Utililty Methods Integer Mod

List of utility methods to do Integer Mod

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Description

The list of methods to do Integer Mod are organized into topic(s).

Method

intmodInverse(int a, int n)
calculates and returns the inverse of a modulo n, both of which should be positive. 
int i = n, v = 0, d = 1;
while (a > 0) {
    int t = i / a, x = a;
    a = i % x;
    i = x;
    x = d;
    d = v - t * x;
    v = x;
...
intmodInverse(int n, int mod)
mod Inverse 
int[] g = extgcd(mod, n);
if (g[0] != 1) {
    return -1; 
} else {
    return reduce(g[2], mod);
intmodMultiply(long a, long b, int m)
Modular multiplication.
Returns ( a * b )( mod m ).
Differs from ( a * b ) % m in that it always returns non-negative value and never overflows.
If m = 0, #NOT_FOUND is returned. 
if (m <= 0) {
    if (m == 0)
        return NOT_FOUND;
    m = -m;
a %= m;
b %= m;
a = (a * b) % m;
...
intmodPos(int divisor, int dividend)
Calculates (value mod size). 
return divisor >= 0 ? divisor % dividend : ((divisor + 1) % dividend) - 1 + dividend;
intmodSubtract(long a, long b, int m)
Modular subtraction.
Returns ( a - b )( mod m ).
Differs from ( a - b ) % m in that it always returns non-negative value and never overflows.
If m = 0, #NOT_FOUND is returned. 
if (m <= 0) {
    if (m == 0)
        return NOT_FOUND;
    m = -m;
a %= m;
b %= m;
a = (a - b) % m;
...
intmodularExp(long base, long exp, int modulus)
Compute modular exponentiation in O(log exp). 
base = base % modulus; 
int toRet = 1;
long[] modExpResults = new long[(int) log2(exp + 1) + 1]; 
modExpResults[0] = (base % modulus); 
for (int i = 1; i < modExpResults.length; i++) {
    modExpResults[i] = (modExpResults[i - 1] * modExpResults[i - 1]) % modulus;
int counter = 0;
...
int[]modularInverses(int p)
This function returns the multiplicative inverses of the integers [0, 1, ..., p-1] in mod p arithmetic. 
int[] inverses = new int[p];
for (int i = 1; i < p; i++) {
    int inverse = 0;
    for (int j = 1; j < p; j++) {
        if (((j * i) % p) == 1) {
            inverse = j;
            break;
    if (inverse == 0) {
        throw new IllegalArgumentException(p + " is not a prime.");
    inverses[i] = inverse;
return inverses;
intmodularInvert(int num, int modulus)
Returns modular inverse of given number with given modulus 
int tmp; 
return ((tmp = (extendedEuclidian(modulus, num)[1] % modulus)) > 0) ? tmp : tmp + modulus;
intmodulateCircularIndex(int index, int seqLength)
Takes a point on a circular location and moves it left until it falls at the earliest possible point that represents the same base. 
if (seqLength == 0) {
    return index;
while (index > seqLength) {
    index -= seqLength;
return index;
intmodulo(int a, int b)
Performs a modulus operation in Python style. 
if (b == 0)
    throw new IllegalArgumentException("Division by Zero!");
if (a > 0 && b > 0 && b > a)
    return a;
boolean isMinus = Math.abs(b - (a - b)) < Math.abs(b - (a + b));
if (isMinus) {
    while (a >= b) {
        a -= b;
...