package im.actor.runtime.crypto.primitives.curve25519;
// Disabling Bounds checks for speeding up calculations
/*-[
#define J2OBJC_DISABLE_ARRAY_BOUND_CHECKS 1
]-*/
public class fe_tobytes {
//CONVERT #include "fe.h"
/*
Preconditions:
|h| bounded by 1.1*2^26,1.1*2^25,1.1*2^26,1.1*2^25,etc.
Write p=2^255-19; q=floor(h/p).
Basic claim: q = floor(2^(-255)(h + 19 2^(-25)h9 + 2^(-1))).
Proof:
Have |h|<=p so |q|<=1 so |19^2 2^(-255) q|<1/4.
Also have |h-2^230 h9|<2^231 so |19 2^(-255)(h-2^230 h9)|<1/4.
Write y=2^(-1)-19^2 2^(-255)q-19 2^(-255)(h-2^230 h9).
Then 0<y<1.
Write r=h-pq.
Have 0<=r<=p-1=2^255-20.
Thus 0<=r+19(2^-255)r<r+19(2^-255)2^255<=2^255-1.
Write x=r+19(2^-255)r+y.
Then 0<x<2^255 so floor(2^(-255)x) = 0 so floor(q+2^(-255)x) = q.
Have q+2^(-255)x = 2^(-255)(h + 19 2^(-25) h9 + 2^(-1))
so floor(2^(-255)(h + 19 2^(-25) h9 + 2^(-1))) = q.
*/
public static void fe_tobytes(byte[] s, int[] h) {
int h0 = h[0];
int h1 = h[1];
int h2 = h[2];
int h3 = h[3];
int h4 = h[4];
int h5 = h[5];
int h6 = h[6];
int h7 = h[7];
int h8 = h[8];
int h9 = h[9];
int q;
int carry0;
int carry1;
int carry2;
int carry3;
int carry4;
int carry5;
int carry6;
int carry7;
int carry8;
int carry9;
q = (19 * h9 + (((int) 1) << 24)) >> 25;
q = (h0 + q) >> 26;
q = (h1 + q) >> 25;
q = (h2 + q) >> 26;
q = (h3 + q) >> 25;
q = (h4 + q) >> 26;
q = (h5 + q) >> 25;
q = (h6 + q) >> 26;
q = (h7 + q) >> 25;
q = (h8 + q) >> 26;
q = (h9 + q) >> 25;
/* Goal: Output h-(2^255-19)q, which is between 0 and 2^255-20. */
h0 += 19 * q;
/* Goal: Output h-2^255 q, which is between 0 and 2^255-20. */
carry0 = h0 >> 26;
h1 += carry0;
h0 -= carry0 << 26;
carry1 = h1 >> 25;
h2 += carry1;
h1 -= carry1 << 25;
carry2 = h2 >> 26;
h3 += carry2;
h2 -= carry2 << 26;
carry3 = h3 >> 25;
h4 += carry3;
h3 -= carry3 << 25;
carry4 = h4 >> 26;
h5 += carry4;
h4 -= carry4 << 26;
carry5 = h5 >> 25;
h6 += carry5;
h5 -= carry5 << 25;
carry6 = h6 >> 26;
h7 += carry6;
h6 -= carry6 << 26;
carry7 = h7 >> 25;
h8 += carry7;
h7 -= carry7 << 25;
carry8 = h8 >> 26;
h9 += carry8;
h8 -= carry8 << 26;
carry9 = h9 >> 25;
h9 -= carry9 << 25;
/* h10 = carry9 */
/*
Goal: Output h0+...+2^255 h10-2^255 q, which is between 0 and 2^255-20.
Have h0+...+2^230 h9 between 0 and 2^255-1;
evidently 2^255 h10-2^255 q = 0.
Goal: Output h0+...+2^230 h9.
*/
s[0] = (byte) (h0 >> 0);
s[1] = (byte) (h0 >> 8);
s[2] = (byte) (h0 >> 16);
s[3] = (byte) ((h0 >> 24) | (h1 << 2));
s[4] = (byte) (h1 >> 6);
s[5] = (byte) (h1 >> 14);
s[6] = (byte) ((h1 >> 22) | (h2 << 3));
s[7] = (byte) (h2 >> 5);
s[8] = (byte) (h2 >> 13);
s[9] = (byte) ((h2 >> 21) | (h3 << 5));
s[10] = (byte) (h3 >> 3);
s[11] = (byte) (h3 >> 11);
s[12] = (byte) ((h3 >> 19) | (h4 << 6));
s[13] = (byte) (h4 >> 2);
s[14] = (byte) (h4 >> 10);
s[15] = (byte) (h4 >> 18);
s[16] = (byte) (h5 >> 0);
s[17] = (byte) (h5 >> 8);
s[18] = (byte) (h5 >> 16);
s[19] = (byte) ((h5 >> 24) | (h6 << 1));
s[20] = (byte) (h6 >> 7);
s[21] = (byte) (h6 >> 15);
s[22] = (byte) ((h6 >> 23) | (h7 << 3));
s[23] = (byte) (h7 >> 5);
s[24] = (byte) (h7 >> 13);
s[25] = (byte) ((h7 >> 21) | (h8 << 4));
s[26] = (byte) (h8 >> 4);
s[27] = (byte) (h8 >> 12);
s[28] = (byte) ((h8 >> 20) | (h9 << 6));
s[29] = (byte) (h9 >> 2);
s[30] = (byte) (h9 >> 10);
s[31] = (byte) (h9 >> 18);
}
}