org.whispersystems.curve25519.java.fe_isnegative Maven / Gradle / Ivy

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Curve25519 library for Java

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package org.whispersystems.curve25519.java;

public class fe_isnegative {

//CONVERT #include "fe.h"

/*
return 1 if f is in {1,3,5,...,q-2}
return 0 if f is in {0,2,4,...,q-1}

Preconditions:
   |f| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
*/

    public static int fe_isnegative(int[] f) {
        byte[] s = new byte[32];
        fe_tobytes.fe_tobytes(s, f);
        return s[0] & 1;
    }


}