Add a FastRandomContext::randrange and use it

2 files changed, 38 insertions, 0 deletions

diff --git a/src/test/crypto_tests.cpp b/src/test/crypto_tests.cpp
index a20182afb8..72e562808a 100644
--- a/src/test/crypto_tests.cpp
+++ b/src/test/crypto_tests.cpp
@@ -10,6 +10,7 @@
 #include "crypto/sha512.h"
 #include "crypto/hmac_sha256.h"
 #include "crypto/hmac_sha512.h"
+#include "random.h"
 #include "utilstrencodings.h"
 #include "test/test_bitcoin.h"
 #include "test/test_random.h"
@@ -484,4 +485,26 @@ BOOST_AUTO_TEST_CASE(chacha20_testvector)
                  "fab78c9");
 }
 
+BOOST_AUTO_TEST_CASE(countbits_tests)
+{
+    FastRandomContext ctx;
+    for (int i = 0; i <= 64; ++i) {
+        if (i == 0) {
+            // Check handling of zero.
+            BOOST_CHECK_EQUAL(CountBits(0), 0);
+        } else if (i < 10) {
+            for (uint64_t j = 1 << (i - 1); (j >> i) == 0; ++j) {
+                // Exhaustively test up to 10 bits
+                BOOST_CHECK_EQUAL(CountBits(j), i);
+            }
+        } else {
+            for (int k = 0; k < 1000; k++) {
+                // Randomly test 1000 samples of each length above 10 bits.
+                uint64_t j = ((uint64_t)1) << (i - 1) | ctx.randbits(i - 1);
+                BOOST_CHECK_EQUAL(CountBits(j), i);
+            }
+        }
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/random_tests.cpp b/src/test/random_tests.cpp
index 31b993cd38..8596734226 100644
--- a/src/test/random_tests.cpp
+++ b/src/test/random_tests.cpp
@@ -35,4 +35,19 @@ BOOST_AUTO_TEST_CASE(fastrandom_tests)
     BOOST_CHECK(ctx3.rand64() != ctx4.rand64()); // extremely unlikely to be equal
 }
 
+BOOST_AUTO_TEST_CASE(fastrandom_randbits)
+{
+    FastRandomContext ctx1;
+    FastRandomContext ctx2;
+    for (int bits = 0; bits < 63; ++bits) {
+        for (int j = 0; j < 1000; ++j) {
+            uint64_t rangebits = ctx1.randbits(bits);
+            BOOST_CHECK_EQUAL(rangebits >> bits, 0);
+            uint64_t range = ((uint64_t)1) << bits | rangebits;
+            uint64_t rand = ctx2.randrange(range);
+            BOOST_CHECK(rand < range);
+        }
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()