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      1 package org.bouncycastle.math.ec.custom.sec;
      2 
      3 import java.math.BigInteger;
      4 
      5 import org.bouncycastle.math.raw.Nat;
      6 import org.bouncycastle.math.raw.Nat512;
      7 
      8 public class SecP521R1Field
      9 {
     10     // 2^521 - 1
     11     static final int[] P = new int[]{ 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF,
     12         0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0xFFFFFFFF, 0x1FF };
     13     private static final int P16 = 0x1FF;
     14 
     15     public static void add(int[] x, int[] y, int[] z)
     16     {
     17         int c = Nat.add(16, x, y, z) + x[16] + y[16];
     18         if (c > P16 || (c == P16 && Nat.eq(16, z, P)))
     19         {
     20             c += Nat.inc(16, z);
     21             c &= P16;
     22         }
     23         z[16] = c;
     24     }
     25 
     26     public static void addOne(int[] x, int[] z)
     27     {
     28         int c = Nat.inc(16, x, z) + x[16];
     29         if (c > P16 || (c == P16 && Nat.eq(16, z, P)))
     30         {
     31             c += Nat.inc(16, z);
     32             c &= P16;
     33         }
     34         z[16] = c;
     35     }
     36 
     37     public static int[] fromBigInteger(BigInteger x)
     38     {
     39         int[] z = Nat.fromBigInteger(521, x);
     40         if (Nat.eq(17, z, P))
     41         {
     42             Nat.zero(17, z);
     43         }
     44         return z;
     45     }
     46 
     47     public static void half(int[] x, int[] z)
     48     {
     49         int x16 = x[16];
     50         int c = Nat.shiftDownBit(16, x, x16, z);
     51         z[16] = (x16 >>> 1) | (c >>> 23);
     52     }
     53 
     54     public static void multiply(int[] x, int[] y, int[] z)
     55     {
     56         int[] tt = Nat.create(33);
     57         implMultiply(x, y, tt);
     58         reduce(tt, z);
     59     }
     60 
     61     public static void negate(int[] x, int[] z)
     62     {
     63         if (Nat.isZero(17, x))
     64         {
     65             Nat.zero(17, z);
     66         }
     67         else
     68         {
     69             Nat.sub(17, P, x, z);
     70         }
     71     }
     72 
     73     public static void reduce(int[] xx, int[] z)
     74     {
     75 //        assert xx[32] >>> 18 == 0;
     76 
     77         int xx32 = xx[32];
     78         int c = Nat.shiftDownBits(16, xx, 16, 9, xx32, z, 0) >>> 23;
     79         c += xx32 >>> 9;
     80         c += Nat.addTo(16, xx, z);
     81         if (c > P16 || (c == P16 && Nat.eq(16, z, P)))
     82         {
     83             c += Nat.inc(16, z);
     84             c &= P16;
     85         }
     86         z[16] = c;
     87     }
     88 
     89     public static void reduce23(int[] z)
     90     {
     91         int z16 = z[16];
     92         int c = Nat.addWordTo(16, z16 >>> 9, z) + (z16 & P16);
     93         if (c > P16 || (c == P16 && Nat.eq(16, z, P)))
     94         {
     95             c += Nat.inc(16, z);
     96             c &= P16;
     97         }
     98         z[16] = c;
     99     }
    100 
    101     public static void square(int[] x, int[] z)
    102     {
    103         int[] tt = Nat.create(33);
    104         implSquare(x, tt);
    105         reduce(tt, z);
    106     }
    107 
    108     public static void squareN(int[] x, int n, int[] z)
    109     {
    110 //        assert n > 0;
    111 
    112         int[] tt = Nat.create(33);
    113         implSquare(x, tt);
    114         reduce(tt, z);
    115 
    116         while (--n > 0)
    117         {
    118             implSquare(z, tt);
    119             reduce(tt, z);
    120         }
    121     }
    122 
    123     public static void subtract(int[] x, int[] y, int[] z)
    124     {
    125         int c = Nat.sub(16, x, y, z) + x[16] - y[16];
    126         if (c < 0)
    127         {
    128             c += Nat.dec(16, z);
    129             c &= P16;
    130         }
    131         z[16] = c;
    132     }
    133 
    134     public static void twice(int[] x, int[] z)
    135     {
    136         int x16 = x[16];
    137         int c = Nat.shiftUpBit(16, x, x16 << 23, z) | (x16 << 1);
    138         z[16] = c & P16;
    139     }
    140 
    141     protected static void implMultiply(int[] x, int[] y, int[] zz)
    142     {
    143         Nat512.mul(x, y, zz);
    144 
    145         int x16 = x[16], y16 = y[16];
    146         zz[32] = Nat.mul31BothAdd(16, x16, y, y16, x, zz, 16) + (x16 * y16);
    147     }
    148 
    149     protected static void implSquare(int[] x, int[] zz)
    150     {
    151         Nat512.square(x, zz);
    152 
    153         int x16 = x[16];
    154         zz[32] = Nat.mulWordAddTo(16, x16 << 1, x, 0, zz, 16) + (x16 * x16);
    155     }
    156 }
    157