Add CashAddr Address Format

Ported from Bitcoin Unlimited, Bitcoin ABC

src/random.h

@@ -34,11 +34,80 @@ void GetStrongRandBytes(unsigned char* buf, int num);
 void seed_insecure_rand(bool fDeterministic = false);
 
 /**
- * MWC RNG of George Marsaglia
- * This is intended to be fast. It has a period of 2^59.3, though the
- * least significant 16 bits only have a period of about 2^30.1.
- *
- * @return random value
+ * Fast randomness source. This is seeded once with secure random data, but
+ * is completely deterministic and insecure after that.
+ * This class is not thread-safe.
+ */
+class FastRandomContext
+{
+private:
+    uint64_t bitbuf;
+    int bitbuf_size;
+
+    void FillBitBuffer()
+    {
+        bitbuf = rand64();
+        bitbuf_size = 64;
+    }
+
+public:
+    explicit FastRandomContext(bool fDeterministic = false);
+
+    uint32_t Rz;
+    uint32_t Rw;
+
+    uint32_t rand32()
+    {
+        Rz = 36969 * (Rz & 65535) + (Rz >> 16);
+        Rw = 18000 * (Rw & 65535) + (Rw >> 16);
+        return (Rw << 16) + Rz;
+    }
+
+    uint64_t rand64()
+    {
+        uint64_t a = rand32();
+        uint64_t b = rand32();
+        return (b << 32) + a;
+    }
+
+    bool randbool() { return rand32() & 1; }
+    uint64_t randbits(int bits)
+    {
+        if (bits == 0)
+        {
+            return 0;
+        }
+        else if (bits > 32)
+        {
+            return rand64() >> (64 - bits);
+        }
+        else
+        {
+            if (bitbuf_size < bits)
+                FillBitBuffer();
+
+            uint64_t ret = bitbuf & (~uint64_t(0) >> (64 - bits));
+            bitbuf >>= bits;
+            bitbuf_size -= bits;
+            return ret;
+        }
+    }
+};
+
+/* Number of random bytes returned by GetOSRand.
+ * When changing this constant make sure to change all call sites, and make
+ * sure that the underlying OS APIs for all platforms support the number.
+ * (many cap out at 256 bytes).
+ */
+static const ssize_t NUM_OS_RANDOM_BYTES = 32;
+
+/** Get 32 bytes of system entropy. Do not use this in application code: use
+ * GetStrongRandBytes instead.
+ */
+void GetOSRand(unsigned char *ent32);
+
+/** Check that OS randomness is available and returning the requested number
+ * of bytes.
  */
 extern uint32_t insecure_rand_Rz;
 extern uint32_t insecure_rand_Rw;