import java.security.MessageDigest;
// import java.security.NoSuchAlgorithmException;

// public final class SHA1Generator extends RandomNumberGenerator {
public final class SHA1Generator {
        // internal constants
        private final static int POS_MASK = 0x7fffffff;
        private final static int LOWBYTE = 0xFF;

        // internal rng state
        private byte[]  state = new byte[20];
        private MessageDigest shamd;

        // new rng from seed
        public SHA1Generator(int seedarg) {
                byte[] seedstate = new byte[20];
                for (int i=0; i<16; i++) seedstate[i]=0;
                seedstate[16] = (byte)(LOWBYTE & (seedarg >> 24));
                seedstate[17] = (byte)(LOWBYTE & (seedarg >> 16));
                seedstate[18] = (byte)(LOWBYTE & (seedarg >> 8));
                seedstate[19] = (byte)(LOWBYTE & (seedarg >> 0));
                try {
                        shamd = MessageDigest.getInstance("SHA-1");
                        shamd.update(seedstate);
                        state = shamd.digest();
                } catch (java.security.NoSuchAlgorithmException bogus) {
                        System.out.println("java.security.NoSuchAlgorithmException");
                        System.exit(0);
                }
        };

        // New rng from existing rng
        public SHA1Generator(SHA1Generator parent, int spawnnumber) {
                byte[]  seedstate = new byte[4];
                seedstate[0] = (byte)(LOWBYTE & (spawnnumber >> 24));
                seedstate[1] = (byte)(LOWBYTE & (spawnnumber >> 16));
                seedstate[2] = (byte)(LOWBYTE & (spawnnumber >> 8));
                seedstate[3] = (byte)(LOWBYTE & (spawnnumber >> 0));
                try {
                        shamd = MessageDigest.getInstance("SHA-1");
                        shamd.update(parent.state);
                        shamd.update(seedstate);
                        state = shamd.digest();
                } catch (java.security.NoSuchAlgorithmException bogus) {
                        System.out.println("java.security.NoSuchAlgorithmException");
                        System.exit(0);
                }
        };

        // Return next random number
        public int nextrand() {
                int d;
                shamd.update(state);
                state = shamd.digest();
                d = 0x7f   & state[16];
                d = (d<<8) | (state[17] & 0xff);
                d = (d<<8) | (state[18] & 0xff);
                d = (d<<8) | (state[19] & 0xff);
                return d;
        };

        // return current random number (no advance)
        public int rand() {
                int d;
                d = 0x7f   & state[16];
                d = (d<<8) | (state[17] & 0xff);
                d = (d<<8) | (state[18] & 0xff);
                d = (d<<8) | (state[19] & 0xff);
                return d&POS_MASK;
        };

        // describe the state of the RNG
        public String showstate() {
                String[] hex = {"0","1","2","3","4","5","6","7","8","9","A","B","C","D","E","F"};
                String sha1state = "SHA1 state=|";
                for (int i=0; i<20; i++) {
                        sha1state += hex[((state[i]>>4)&0x0F)];
                        sha1state += hex[((state[i]>>0)&0x0F)];
                        sha1state += "|";
                }
                return sha1state;
        };

        // describe the RNG
        public String showtype() {
                return ("SHA-1 160 bits");
        };

        public static void main(String[] args) {
                double et=0.0;
                int i=0;
                int j=0;
                int r=0;
                int NUM_RNG_SPAWNS = 1600;
                SHA1Generator parent = new SHA1Generator(0);
                SHA1Generator[] child = new SHA1Generator[NUM_RNG_SPAWNS];
                for (i=0; i<2000; i++) {
                        r=parent.nextrand();
                }
                for (i=0; i<10; i++) {
                        r=parent.nextrand();
                        System.out.println(parent.showstate()+", NEXT="+r);
                }
                parent = new SHA1Generator(0);
                for (j=1; j<NUM_RNG_SPAWNS; j++) {
                        child[j] = new SHA1Generator(parent,j);
                        for (i=0; i<1000; i++) {
                                r=child[j].nextrand();
                                r=parent.nextrand();
                        }
                }
                parent = new SHA1Generator(0);
                for (j=1; j<20; j++) {
                        child[j] = new SHA1Generator(parent,j);
                        for (i=0; i<NUM_RNG_SPAWNS; i++) {
                                r=child[j].nextrand();
                                r=parent.nextrand();
                        }
                        r=child[j].nextrand();
                        System.out.println(child[j].showstate()+", NEXT="+r);
                }
                System.out.println("Timing "+NUM_RNG_SPAWNS+" RNG spawns ...");
                parent = new SHA1Generator(0);
                et = -(double)System.nanoTime();
                for (i = 1; i < NUM_RNG_SPAWNS; i++) {
                        child[i] = new SHA1Generator(parent,i);
                }
                et += (double)System.nanoTime();
                et *= 1.0e-09;
                System.out.println("Wall clock time = "+et+" sec, "
                                    +et/NUM_RNG_SPAWNS+" sec/spawn, "
                                    +NUM_RNG_SPAWNS/et+" spawns/sec");
                System.out.println("Number of Successful Spawns i="+i);
                et = -(double)System.nanoTime();
                for (i=0; i<1000000; i++) {
				}
                et += (double)System.nanoTime();
                et *= 1.0e-09;
                System.out.println("wall="+et+"   rnd/s="+1000000./et+"   s/rnd="+et/1000000.);
        }
}