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Curve25519 library for Java
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;
}
}