tests: Add fuzzing harness for Golomb-Rice coding (GolombRiceEncode/GolombRiceDecode)

1 files changed, 43 insertions, 0 deletions

diff --git a/src/util/golombrice.h b/src/util/golombrice.h
new file mode 100644
index 0000000000..425e7f6681
--- /dev/null
+++ b/src/util/golombrice.h
@@ -0,0 +1,43 @@
+// Copyright (c) 2018-2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_GOLOMBRICE_H
+#define BITCOIN_UTIL_GOLOMBRICE_H
+
+#include <streams.h>
+
+#include <cstdint>
+
+template <typename OStream>
+void GolombRiceEncode(BitStreamWriter<OStream>& bitwriter, uint8_t P, uint64_t x)
+{
+    // Write quotient as unary-encoded: q 1's followed by one 0.
+    uint64_t q = x >> P;
+    while (q > 0) {
+        int nbits = q <= 64 ? static_cast<int>(q) : 64;
+        bitwriter.Write(~0ULL, nbits);
+        q -= nbits;
+    }
+    bitwriter.Write(0, 1);
+
+    // Write the remainder in P bits. Since the remainder is just the bottom
+    // P bits of x, there is no need to mask first.
+    bitwriter.Write(x, P);
+}
+
+template <typename IStream>
+uint64_t GolombRiceDecode(BitStreamReader<IStream>& bitreader, uint8_t P)
+{
+    // Read unary-encoded quotient: q 1's followed by one 0.
+    uint64_t q = 0;
+    while (bitreader.Read(1) == 1) {
+        ++q;
+    }
+
+    uint64_t r = bitreader.Read(P);
+
+    return (q << P) + r;
+}
+
+#endif // BITCOIN_UTIL_GOLOMBRICE_H