ceph/src/boost/boost/beast/zlib/detail/bitstream.hpp

   1 //
   2 // Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
   3 //
   4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   6 //
   7 // Official repository: https://github.com/boostorg/beast
   8 //
   9 // This is a derivative work based on Zlib, copyright below:
  10 /*
  11     Copyright (C) 1995-2013 Jean-loup Gailly and Mark Adler
  12
  13     This software is provided 'as-is', without any express or implied
  14     warranty.  In no event will the authors be held liable for any damages
  15     arising from the use of this software.
  16
  17     Permission is granted to anyone to use this software for any purpose,
  18     including commercial applications, and to alter it and redistribute it
  19     freely, subject to the following restrictions:
  20
  21     1. The origin of this software must not be misrepresented; you must not
  22        claim that you wrote the original software. If you use this software
  23        in a product, an acknowledgment in the product documentation would be
  24        appreciated but is not required.
  25     2. Altered source versions must be plainly marked as such, and must not be
  26        misrepresented as being the original software.
  27     3. This notice may not be removed or altered from any source distribution.
  28
  29     Jean-loup Gailly        Mark Adler
  30     jloup@gzip.org          madler@alumni.caltech.edu
  31
  32     The data format used by the zlib library is described by RFCs (Request for
  33     Comments) 1950 to 1952 in the files http://tools.ietf.org/html/rfc1950
  34     (zlib format), rfc1951 (deflate format) and rfc1952 (gzip format).
  35 */
  36
  37 #ifndef BOOST_BEAST_ZLIB_DETAIL_BITSTREAM_HPP
  38 #define BOOST_BEAST_ZLIB_DETAIL_BITSTREAM_HPP
  39
  40 #include <boost/assert.hpp>
  41 #include <cstdint>
  42 #include <iterator>
  43
  44 namespace boost {
  45 namespace beast {
  46 namespace zlib {
  47 namespace detail {
  48
  49 class bitstream
  50 {
  51     using value_type = std::uint32_t;
  52
  53     value_type v_ = 0;
  54     unsigned n_ = 0;
  55
  56 public:
  57     // returns the number of bits in the reservoir
  58     unsigned
  59     size() const
  60     {
  61         return n_;
  62     }
  63
  64     // discard n bits
  65     void
  66     drop(std::size_t n)
  67     {
  68         BOOST_ASSERT(n <= n_);
  69         n_ -= static_cast<unsigned>(n);
  70         v_ >>= n;
  71     }
  72
  73     // flush everything
  74     void
  75     flush()
  76     {
  77         n_ = 0;
  78         v_ = 0;
  79     }
  80
  81     // flush to the next byte boundary
  82     void
  83     flush_byte()
  84     {
  85         drop(n_ % 8);
  86     }
  87
  88     // ensure at least n bits
  89     template<class FwdIt>
  90     bool
  91     fill(std::size_t n, FwdIt& first, FwdIt const& last);
  92
  93     // fill 8 bits, unchecked
  94     template<class FwdIt>
  95     void
  96     fill_8(FwdIt& it);
  97
  98     // fill 16 bits, unchecked
  99     template<class FwdIt>
 100     void
 101     fill_16(FwdIt& it);
 102
 103     // return n bits
 104     template<class Unsigned>
 105     void
 106     peek(Unsigned& value, std::size_t n);
 107
 108     // return everything in the reservoir
 109     value_type
 110     peek_fast() const
 111     {
 112         return v_;
 113     }
 114
 115     // return n bits, and consume
 116     template<class Unsigned>
 117     void
 118     read(Unsigned& value, std::size_t n);
 119
 120     // rewind by the number of whole bytes stored (unchecked)
 121     template<class BidirIt>
 122     void
 123     rewind(BidirIt& it);
 124 };
 125
 126 template<class FwdIt>
 127 bool
 128 bitstream::
 129 fill(std::size_t n, FwdIt& first, FwdIt const& last)
 130 {
 131     while(n_ < n)
 132     {
 133         if(first == last)
 134             return false;
 135         v_ += static_cast<value_type>(*first++) << n_;
 136         n_ += 8;
 137     }
 138     return true;
 139 }
 140
 141 template<class FwdIt>
 142 void
 143 bitstream::
 144 fill_8(FwdIt& it)
 145 {
 146     v_ += static_cast<value_type>(*it++) << n_;
 147     n_ += 8;
 148 }
 149
 150 template<class FwdIt>
 151 void
 152 bitstream::
 153 fill_16(FwdIt& it)
 154 {
 155     v_ += static_cast<value_type>(*it++) << n_;
 156     n_ += 8;
 157     v_ += static_cast<value_type>(*it++) << n_;
 158     n_ += 8;
 159 }
 160
 161 template<class Unsigned>
 162 void
 163 bitstream::
 164 peek(Unsigned& value, std::size_t n)
 165 {
 166     BOOST_ASSERT(n <= sizeof(value)*8);
 167     BOOST_ASSERT(n <= n_);
 168     value = static_cast<Unsigned>(
 169         v_ & ((1ULL << n) - 1));
 170 }
 171
 172 template<class Unsigned>
 173 void
 174 bitstream::
 175 read(Unsigned& value, std::size_t n)
 176 {
 177     BOOST_ASSERT(n < sizeof(v_)*8);
 178     BOOST_ASSERT(n <= n_);
 179     value = static_cast<Unsigned>(
 180         v_ & ((1ULL << n) - 1));
 181     v_ >>= n;
 182     n_ -= static_cast<unsigned>(n);
 183 }
 184
 185 template<class BidirIt>
 186 void
 187 bitstream::
 188 rewind(BidirIt& it)
 189 {
 190     auto len = n_ >> 3;
 191     it = std::prev(it, len);
 192     n_ &= 7;
 193     v_ &= (1U << n_) - 1;
 194 }
 195
 196 } // detail
 197 } // zlib
 198 } // beast
 199 } // boost
 200
 201 #endif