bdlde_crc32.h

Go to the documentation of this file.

/// @file bdlde_crc32.h
///
/// The content of this file has been pre-processed for Doxygen.
///
 
 
// bdlde_crc32.h                                                      -*-C++-*-
#ifndef INCLUDED_BDLDE_CRC32
#define INCLUDED_BDLDE_CRC32
 
#include <bsls_ident.h>
BSLS_IDENT("$Id: $")
 
/// @defgroup bdlde_crc32 bdlde_crc32
/// @brief  Provide a mechanism for computing the CRC-32 checksum of a dataset.
/// @addtogroup bdl
/// @{
/// @addtogroup bdlde
/// @{
/// @addtogroup bdlde_crc32
/// @{
///
/// <h1> Outline </h1>
/// * <a href="#bdlde_crc32-purpose"> Purpose</a>
/// * <a href="#bdlde_crc32-classes"> Classes </a>
/// * <a href="#bdlde_crc32-description"> Description </a>
///   * <a href="#bdlde_crc32-usage"> Usage </a>
///     * <a href="#bdlde_crc32-example-1-basic-usage"> Example 1: Basic Usage </a>
///
/// # Purpose {#bdlde_crc32-purpose}
/// Provide a mechanism for computing the CRC-32 checksum of a dataset.
///
/// # Classes {#bdlde_crc32-classes}
///
/// -  bdlde::Crc32: stores and updates a CRC-32 checksum
///
/// @see 
///
/// # Description {#bdlde_crc32-description}
/// This component implements a mechanism for computing, updating,
/// and streaming a CRC-32 checksum (a cyclic redundancy check comprised of 32
/// bits).  This checksum is a strong and fast technique for determining whether
/// or not a message was received without errors.  Note that a CRC-32 checksum
/// does not aid in error correction and is not naively useful in any sort of
/// cryptographic application.  Compared to other methods such as MD5 and
/// SHA-256, it is relatively easy to find alternate texts with identical
/// checksum.
///
/// ## Usage {#bdlde_crc32-usage}
///
///
/// This section illustrates intended use of this component.
///
/// ### Example 1: Basic Usage {#bdlde_crc32-example-1-basic-usage}
///
///
/// The following snippets of code illustrate a typical use of the
/// `bdlde::Crc32` class.  Each function would typically execute in separate
/// processes or potentially on separate machines.  The `senderExample` function
/// below demonstrates how a message sender can write a message and its CRC-32
/// checksum to a `bdex` output stream.  Note that `Out` may be a `typedef` of
/// any class that implements the `bslx::OutStream` protocol:
/// @code
/// /// Write a message and its CRC-32 checksum to the specified `output`
/// /// stream.
/// void senderExample(Out& output)
/// {
///     // prepare a message
///     bsl::string message = "This is a test message.";
///
///     // generate a checksum for `message`
///     bdlde::Crc32 crc(message.data(), message.length());
///
///     // write the message to `output`
///     output << message;
///
///     // write the checksum to `output`
///     const int VERSION = 1;
///     crc.bdexStreamOut(output, VERSION);
/// }
/// @endcode
/// The `receiverExample` function below illustrates how a message receiver can
/// read a message and its CRC-32 checksum from a `bdex` input stream, then
/// perform a local CRC-32 computation to verify that the message was received
/// intact.  Note that `In` may be a `typedef` of any class that implements the
/// `bslx::InStream` protocol:
/// @code
/// /// Read a message and its CRC-32 checksum from the specified `input`
/// /// stream, and verify the integrity of the message.
/// void receiverExample(In& input)
/// {
///     // read the message from `input`
///     bsl::string message;
///     input >> message;
///
///     // read the checksum from `input`
///     bdlde::Crc32 crc;
///     const int VERSION = 1;
///     crc.bdexStreamIn(input, VERSION);
///
///     // locally compute the checksum of the received `message`
///     bdlde::Crc32 crcLocal;
///     crcLocal.update(message.data(), message.length());
///
///     // verify that the received and locally-computed checksums match
///     assert(crcLocal == crc);
/// }
/// @endcode
/// @}
/** @} */
/** @} */
 
/** @addtogroup bdl
 * @{
 */
/** @addtogroup bdlde
 * @{
 */
/** @addtogroup bdlde_crc32
 * @{
 */
 
#include <bdlscm_version.h>
 
#include <bsls_assert.h>
 
#include <bsl_cstddef.h>
#include <bsl_iosfwd.h>
 
 
namespace bdlde {
 
                                // ===========
                                // class Crc32
                                // ===========
 
/// This class represents a CRC-32 checksum value that can be updated as
/// data is provided.
///
/// More generally, this class supports a complete set of *value semantic*
/// operations, including copy construction, assignment, equality comparison,
/// `ostream` printing, and `bdex` serialization.  (A precise operational
/// definition of when two objects have the same value can be found in the
/// description of `operator==` for the class.) This class is *exception
/// neutral* with no guarantee of rollback: if an exception is thrown during
/// the invocation of a method on a pre-existing object, the class is left in a
/// valid state, but its value is undefined.  In no event is memory leaked.
/// Finally, *aliasing* (e.g., using all or part of an object as both source
/// and destination) is supported in all cases.
///
/// See @ref bdlde_crc32 
class Crc32 {
 
    // DATA
    unsigned int d_crc;  // value of the checksum ^ 0xffffffff
 
    // FRIENDS
    friend bool operator==(const Crc32&, const Crc32&);
 
  public:
    // CLASS METHODS
 
    /// Return the maximum valid BDEX format version, as indicated by the
    /// specified `versionSelector`, to be passed to the `bdexStreamOut`
    /// method.  Note that the `versionSelector` is expected to be formatted
    /// as `yyyymmdd`, a date representation.  See the `bslx` package-level
    /// documentation for more information on BDEX streaming of
    /// value-semantic types and containers.
    static int maxSupportedBdexVersion(int versionSelector);
 
    // CREATORS
 
    /// Construct a checksum having the value corresponding to no data
    /// having been provided (i.e., having the value 0).
    Crc32();
 
    /// Construct a checksum corresponding to the specified `data` having
    /// the specified `length` (in bytes).  Note that if `data` is 0, then
    /// `length` also must be 0.
    Crc32(const void *data, bsl::size_t length);
 
    /// Construct a checksum having the value of the specified `original`
    /// checksum.
    Crc32(const Crc32& original);
 
    /// Destroy this object.
     ~Crc32() = default;
 
    // MANIPULATORS
 
    /// Assign to this checksum the value of the specified `rhs` checksum,
    /// and return a reference to this modifiable checksum.
    Crc32& operator=(const Crc32& rhs);
 
    /// Assign to this object the value read from the specified input
    /// `stream` using the specified `version` format, and return a
    /// reference to `stream`.  If `stream` is initially invalid, this
    /// operation has no effect.  If `version` is not supported, this object
    /// is unaltered and `stream` is invalidated but otherwise unmodified.
    /// If `version` is supported but `stream` becomes invalid during this
    /// operation, this object has an undefined, but valid, state.  Note
    /// that no version is read from `stream`.  See the `bslx` package-level
    /// documentation for more information on BDEX streaming of
    /// value-semantic types and containers.
    template <class STREAM>
    STREAM& bdexStreamIn(STREAM& stream, int version);
 
    /// Return the current value of this checksum and set the value of this
    /// checksum to the value the default constructor provides.
    unsigned int checksumAndReset();
 
    /// Reset the value of this checksum to the value the default
    /// constructor provides.
    void reset();
 
    /// Update the value of this checksum to incorporate the specified
    /// `data` having the specified `length`.  If the current state is the
    /// default state, the resultant value of this checksum is the
    /// application of the CRC-32 algorithm upon the currently given `data`
    /// of the given `length`.  If this checksum has been previously
    /// provided data and has not been subsequently reset, the current state
    /// is not the default state and the resultant value is equivalent to
    /// applying the CRC-32 algorithm upon the concatenation of all the
    /// provided data.  Note that if `data` is 0, then `length` also must be
    /// 0.
    void update(const void *data, bsl::size_t length);
 
    // ACCESSORS
 
    /// Write this value to the specified output `stream` using the
    /// specified `version` format, and return a reference to `stream`.
    /// If `stream` is initially invalid, this operation has no effect.
    /// If `version` is not supported, `stream` is invalidated but
    /// otherwise unmodified.  Note that `version` is not written to
    /// `stream`.  See the `bslx` package-level documentation for more
    /// information on BDEX streaming of value-semantic types and
    /// containers.
    template <class STREAM>
    STREAM& bdexStreamOut(STREAM& stream, int version) const;
 
    /// Return the current value of this checksum.
    unsigned int checksum() const;
 
    /// Format this object to the specified output `stream` at the (absolute
    /// value of) the optionally specified indentation `level` and return a
    /// reference to `stream`.  If `level` is specified, optionally specify
    /// `spacesPerLevel`, the number of spaces per indentation level for
    /// this and all of its nested objects.  If `level` is negative,
    /// suppress indentation of the first line.  If `spacesPerLevel` is
    /// negative, format the entire output on one line, suppressing all but
    /// the initial indentation (as governed by `level`).  If `stream` is
    /// not valid on entry, this operation has no effect.
    bsl::ostream& print(bsl::ostream& stream) const;
 
#ifndef BDE_OMIT_INTERNAL_DEPRECATED
    // CLASS METHOD
 
    /// Return the most current `bdex` streaming version number supported by
    /// this class.  (See the package-group-level documentation for more
    /// information on `bdex` streaming of container types.)
    static int maxSupportedBdexVersion();
 
    // ACCESSOR
 
    /// Return the current value of this checksum.
    ///
    /// @deprecated  use method `checksum` instead.
    unsigned int view() const;
#endif // BDE_OMIT_INTERNAL_DEPRECATED
 
};
 
// FREE OPERATORS
 
/// Return `true` if the specified `lhs` and `rhs` checksums have the same
/// value, and `false` otherwise.  Two checksums have the same value if the
/// values obtained from their `checksum` methods are identical.
bool operator==(const Crc32& lhs, const Crc32& rhs);
 
/// Return `true` if the specified `lhs` and `rhs` checksums do not have the
/// same value, and `false` otherwise.  Two checksums do not have the same
/// value if the values obtained from their `checksum` methods differ.
bool operator!=(const Crc32& lhs, const Crc32& rhs);
 
/// Write to the specified output `stream` the specified `checksum` value
/// and return a reference to the modifiable `stream`.
bsl::ostream& operator<<(bsl::ostream& stream, const Crc32& checksum);
 
// ============================================================================
//                        INLINE FUNCTION DEFINITIONS
// ============================================================================
 
                                // -----------
                                // class Crc32
                                // -----------
 
// CLASS METHODS
inline
int Crc32::maxSupportedBdexVersion(int)
{
    return 1;
}
 
// CREATORS
inline
Crc32::Crc32()
: d_crc(0xffffffff)
{
}
 
inline
Crc32::Crc32(const void *data, bsl::size_t length)
: d_crc(0xffffffff)
{
    update(data, length);
}
 
inline
Crc32::Crc32(const Crc32& original)
: d_crc(original.d_crc)
{
}
 
// MANIPULATORS
inline
Crc32& Crc32::operator=(const Crc32& rhs)
{
    d_crc = rhs.d_crc;
    return *this;
}
 
template <class STREAM>
STREAM& Crc32::bdexStreamIn(STREAM& stream, int version)
{
    if (stream) {
        switch (version) {
          case 1: {
            unsigned int crc;
            stream.getUint32(crc);
            if (!stream) {
                return stream;                                        // RETURN
            }
            d_crc = crc;
          } break;
          default: {
            stream.invalidate();
          } break;
        }
    }
    return stream;
}
 
inline
unsigned int Crc32::checksumAndReset()
{
    const unsigned int crc = d_crc;
    d_crc = 0xffffffff;
    return crc ^ 0xffffffff;
}
 
inline
void Crc32::reset()
{
    d_crc = 0xffffffff;
}
 
// ACCESSORS
template <class STREAM>
STREAM& Crc32::bdexStreamOut(STREAM& stream, int version) const
{
    switch (version) {
      case 1: {
        stream.putUint32(d_crc);
      } break;
      default: {
        stream.invalidate();
      } break;
    }
    return stream;
}
 
inline
unsigned int Crc32::checksum() const
{
    return d_crc ^ 0xffffffff;
}
 
#ifndef BDE_OMIT_INTERNAL_DEPRECATED
 
// CLASS METHODS
inline
int Crc32::maxSupportedBdexVersion()
{
    return maxSupportedBdexVersion(0);
}
 
// ACCESSORS
inline
unsigned int Crc32::view() const
{
    return d_crc ^ 0xffffffff;
}
 
#endif // BDE_OMIT_INTERNAL_DEPRECATED
 
}  // close package namespace
 
// FREE OPERATORS
inline
bool bdlde::operator==(const Crc32& lhs, const Crc32& rhs)
{
    return lhs.d_crc == rhs.d_crc;
}
 
inline
bool bdlde::operator!=(const Crc32& lhs, const Crc32& rhs)
{
    return !(lhs == rhs);
}
 
inline
bsl::ostream& bdlde::operator<<(bsl::ostream& stream, const Crc32& checksum)
{
    return checksum.print(stream);
}
 
 
 
#endif
 
// ----------------------------------------------------------------------------
// Copyright 2018 Bloomberg Finance L.P.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// ----------------------------- END-OF-FILE ----------------------------------
 
/** @} */
/** @} */
/** @} */