1// Copyright (c) 2018-present The Bitcoin Core developers
2// Distributed under the MIT software license, see the accompanying
3// file COPYING or http://www.opensource.org/licenses/mit-license.php.
4
5#ifndef BITCOIN_UTIL_GOLOMBRICE_H
6#define BITCOIN_UTIL_GOLOMBRICE_H
7
8#include <util/fastrange.h>
9
10#include <streams.h>
11
12#include <cstdint>
13
14template <typename OStream>
15void GolombRiceEncode(BitStreamWriter<OStream>& bitwriter, uint8_t P, uint64_t x)
16{
17    // Write quotient as unary-encoded: q 1's followed by one 0.
18    uint64_t q = x >> P;
19    while (q > 0) {
20        int nbits = q <= 64 ? static_cast<int>(q) : 64;
21        bitwriter.Write(~0ULL, nbits);
22        q -= nbits;
23    }
24    bitwriter.Write(0, 1);
25
26    // Write the remainder in P bits. Since the remainder is just the bottom
27    // P bits of x, there is no need to mask first.
28    bitwriter.Write(x, P);
29}
30
31template <typename IStream>
32uint64_t GolombRiceDecode(BitStreamReader<IStream>& bitreader, uint8_t P)
33{
34    // Read unary-encoded quotient: q 1's followed by one 0.
35    uint64_t q = 0;
36    while (bitreader.Read(1) == 1) {
37        ++q;
38    }
39
40    uint64_t r = bitreader.Read(P);
41
42    return (q << P) + r;
43}
44
45#endif // BITCOIN_UTIL_GOLOMBRICE_H
46