Add FastRandomContext::rand256() and ::randbytes()

FastRandomContext now provides all functionality that the real Rand* functions
provide.

src/random.cpp

@@ -304,6 +304,26 @@ void FastRandomContext::RandomSeed()
     requires_seed = false;
 }
 
+uint256 FastRandomContext::rand256()
+{
+    if (bytebuf_size < 32) {
+        FillByteBuffer();
+    }
+    uint256 ret;
+    memcpy(ret.begin(), bytebuf + 64 - bytebuf_size, 32);
+    bytebuf_size -= 32;
+    return ret;
+}
+
+std::vector<unsigned char> FastRandomContext::randbytes(size_t len)
+{
+    std::vector<unsigned char> ret(len);
+    if (len > 0) {
+        rng.Output(&ret[0], len);
+    }
+    return ret;
+}
+
 FastRandomContext::FastRandomContext(const uint256& seed) : requires_seed(false), bytebuf_size(0), bitbuf_size(0)
 {
     rng.SetKey(seed.begin(), 32);

src/random.h

@@ -110,9 +110,15 @@ public:
         }
     }
 
+    /** Generate random bytes. */
+    std::vector<unsigned char> randbytes(size_t len);
+
     /** Generate a random 32-bit integer. */
     uint32_t rand32() { return randbits(32); }
 
+    /** generate a random uint256. */
+    uint256 rand256();
+
     /** Generate a random boolean. */
     bool randbool() { return randbits(1); }
 };

src/test/random_tests.cpp

@@ -25,14 +25,21 @@ BOOST_AUTO_TEST_CASE(fastrandom_tests)
     BOOST_CHECK_EQUAL(ctx1.rand32(), ctx2.rand32());
     BOOST_CHECK_EQUAL(ctx1.rand64(), ctx2.rand64());
     BOOST_CHECK_EQUAL(ctx1.randbits(3), ctx2.randbits(3));
+    BOOST_CHECK(ctx1.randbytes(17) == ctx2.randbytes(17));
+    BOOST_CHECK(ctx1.rand256() == ctx2.rand256());
     BOOST_CHECK_EQUAL(ctx1.randbits(7), ctx2.randbits(7));
+    BOOST_CHECK(ctx1.randbytes(128) == ctx2.randbytes(128));
     BOOST_CHECK_EQUAL(ctx1.rand32(), ctx2.rand32());
     BOOST_CHECK_EQUAL(ctx1.randbits(3), ctx2.randbits(3));
+    BOOST_CHECK(ctx1.rand256() == ctx2.rand256());
+    BOOST_CHECK(ctx1.randbytes(50) == ctx2.randbytes(50));
 
     // Check that a nondeterministic ones are not
     FastRandomContext ctx3;
     FastRandomContext ctx4;
     BOOST_CHECK(ctx3.rand64() != ctx4.rand64()); // extremely unlikely to be equal
+    BOOST_CHECK(ctx3.rand256() != ctx4.rand256());
+    BOOST_CHECK(ctx3.randbytes(7) != ctx4.randbytes(7));
 }
 
 BOOST_AUTO_TEST_CASE(fastrandom_randbits)