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powermod(a, -1, m) now gives modular inverse.

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skylarmt 2015-04-13 12:30:02 -06:00
parent 4cd7e62ce4
commit 31751ccb4d
1 changed files with 5 additions and 1 deletions
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6
src/net/apocalypselabs/symat/Functions.java
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@ -175,13 +175,17 @@ public class Functions {
}
/**
* Take (a^b) mod m.
* Take (a^b) mod m. If b is -1, finds the modular inverse of a mod m.
* @param a Number
* @param b Exponent
* @param m Modulus
* @return pow(a,b)%m.
*/
public double powermod(double a, double b, double m) {
if (b == -1) {
BigInteger in = new BigInteger(String.valueOf((int)a));
return in.modInverse(new BigInteger(String.valueOf((int)m))).doubleValue();
}
return (pow(a, b) % m + m) % m;
}