uint_types.h

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/***************************************************************************
 * include/stxxl/bits/common/uint_types.h
 *
 * Class representing a 40-bit or 48-bit unsigned integer encoded in five or
 * six bytes.
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2013 Timo Bingmann <[email protected]>
 *
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#ifndef STXXL_COMMON_UINT_TYPES_HEADER
#define STXXL_COMMON_UINT_TYPES_HEADER

#include <stxxl/bits/config.h>
#include <stxxl/bits/namespace.h>
#include <stxxl/bits/common/utils.h>
#include <stxxl/bits/common/types.h>

#include <limits>
#include <ostream>
#include <cassert>

STXXL_BEGIN_NAMESPACE

/*!
 * \brief Construct an 40-bit or 48-bit unsigned integer stored in five or six
 * bytes.
 *
 * The purpose of this class is to provide integers with smaller data storage
 * footprints when more than 32-bit, but less than 64-bit indexes are
 * needed. This is commonly the case for storing file offsets and indexes. Here
 * smaller types currently suffice for files < 1 TiB or < 16 TiB.
 *
 * The class combines a 32-bit integer with a HighType (either 8-bit or 16-bit)
 * to get a larger type. Only unsigned values are supported, which fits the
 * general application of file offsets.
 *
 * Calculation in uint_pair are generally done by transforming everything to
 * 64-bit data type, so that 64-bit register arithmetic can be used. The
 * exception here is \b increment and \b decrement, which is done directly on
 * the lower/higher part. Not all arithmetic operations are supported, patches
 * welcome if you really need the operations.
 */
#if STXXL_MSVC
#pragma pack(push, 1)
#endif
template <typename HighType>
class uint_pair
{
public:
 //! lower part type, always 32-bit
 typedef uint32 low_type;
 //! higher part type, currently either 8-bit or 16-bit
 typedef HighType high_type;

private:
 //! member containing lower significant integer value
 low_type low;
 //! member containing higher significant integer value
 high_type high;

 //! return highest value storable in lower part, also used as a mask.
 static low_type low_max()
 {
 return std::numeric_limits<low_type>::max();
 }

 //! number of bits in the lower integer part, used a bit shift value.
 static const int low_bits = 8 * sizeof(low_type);

 //! return highest value storable in higher part, also used as a mask.
 static high_type high_max()
 {
 return std::numeric_limits<high_type>::max();
 }

 //! number of bits in the higher integer part, used a bit shift value.
 static const int high_bits = 8 * sizeof(high_type);

public:
 //! number of binary digits (bits) in uint_pair
 static const int digits = low_bits + high_bits;

 //! number of bytes in uint_pair
 static const int bytes = sizeof(low_type) + sizeof(high_type);

 //! empty constructor, does not even initialize to zero!
 inline uint_pair()
 {
 // compile-time assertions about size of low_type
 STXXL_STATIC_ASSERT(8 * sizeof(low_type) == 32);
 // compile-time assertions about size of our data structure, this tests
 // packing of structures by the compiler
 STXXL_STATIC_ASSERT(sizeof(uint_pair) == bytes);
 STXXL_STATIC_ASSERT(sizeof(uint_pair) == digits / 8);
 STXXL_STATIC_ASSERT(digits / 8 == bytes);
 }

 //! construct unit pair from lower and higher parts.
 inline uint_pair(const low_type& l, const high_type& h)
 : low(l), high(h)
 { }

 //! copy constructor
 inline uint_pair(const uint_pair& a)
 : low(a.low), high(a.high)
 { }

 //! const from a simple 32-bit unsigned integer
 inline uint_pair(const uint32& a)
 : low(a), high(0)
 { }

 //! const from a simple 32-bit signed integer
 inline uint_pair(const int32& a)
 : low(a), high(0)
 {
 if (a >= 0)
 low = a;
 else
 low = a, high = high_max();
 }

 //! construct from an uint64 (unsigned long long)
 inline uint_pair(const uint64& a)
 : low(a & low_max()),
 high((a >> low_bits) & high_max())
 {
 // check for overflow
 assert((a >> (low_bits + high_bits)) == 0);
 }

 //! return the number as an uint64 (unsigned long long)
 inline uint64 ull() const
 {
 return ((uint64)high) << low_bits | (uint64)low;
 }

 //! implicit cast to an unsigned long long
 inline operator uint64 () const
 {
 return ull();
 }

 //! return the number as a uint64
 inline uint64 u64() const
 {
 return ((uint64)high) << low_bits | (uint64)low;
 }

 //! prefix increment operator (directly manipulates the integer parts)
 inline uint_pair& operator ++ ()
 {
 if (UNLIKELY(low == low_max()))
 ++high, low = 0;
 else
 ++low;
 return *this;
 }

 //! prefix decrement operator (directly manipulates the integer parts)
 inline uint_pair& operator -- ()
 {
 if (UNLIKELY(low == 0))
 --high, low = low_max();
 else
 --low;
 return *this;
 }

 //! addition operator (uses 64-bit arithmetic)
 inline uint_pair& operator += (const uint_pair& b)
 {
 uint64 add = low + b.low;
 low = add & low_max();
 high += b.high + ((add >> low_bits) & high_max());
 return *this;
 }

 //! equality checking operator
 inline bool operator == (const uint_pair& b) const
 {
 return (low == b.low) && (high == b.high);
 }

 //! inequality checking operator
 inline bool operator != (const uint_pair& b) const
 {
 return (low != b.low) || (high != b.high);
 }

 //! less-than comparison operator
 inline bool operator < (const uint_pair& b) const
 {
 return (high < b.high) || (high == b.high && low < b.low);
 }

 //! less-or-equal comparison operator
 inline bool operator <= (const uint_pair& b) const
 {
 return (high < b.high) || (high == b.high && low <= b.low);
 }

 //! greater comparison operator
 inline bool operator > (const uint_pair& b) const
 {
 return (high > b.high) || (high == b.high && low > b.low);
 }

 //! greater-or-equal comparison operator
 inline bool operator >= (const uint_pair& b) const
 {
 return (high > b.high) || (high == b.high && low >= b.low);
 }

 //! make a uint_pair outputtable via iostreams, using unsigned long long.
 friend std::ostream& operator << (std::ostream& os, const uint_pair& a)
 {
 return os << a.ull();
 }

 //! return an uint_pair instance containing the smallest value possible
 static uint_pair min()
 {
 return uint_pair(std::numeric_limits<low_type>::min(),
 std::numeric_limits<high_type>::min());
 }

 //! return an uint_pair instance containing the largest value possible
 static uint_pair max()
 {
 return uint_pair(std::numeric_limits<low_type>::max(),
 std::numeric_limits<high_type>::max());
 }
}
#if STXXL_MSVC
;
#pragma pack(pop)
#else
__attribute__ ((packed));
#endif

//! Construct a 40-bit unsigned integer stored in five bytes.
typedef uint_pair<uint8> uint40;

//! Construct a 48-bit unsigned integer stored in six bytes.
typedef uint_pair<uint16> uint48;

STXXL_END_NAMESPACE

namespace std {

//! template class providing some numeric_limits fields for uint_pair types.
template <typename HighType>
class numeric_limits<stxxl::uint_pair<HighType> >
{
public:
 //! yes we have information about uint_pair
 static const bool is_specialized = true;

 //! return an uint_pair instance containing the smallest value possible
 static stxxl::uint_pair<HighType> min()
 { return stxxl::uint_pair<HighType>::min(); }

 //! return an uint_pair instance containing the largest value possible
 static stxxl::uint_pair<HighType> max()
 { return stxxl::uint_pair<HighType>::max(); }

 //! return an uint_pair instance containing the smallest value possible
 static stxxl::uint_pair<HighType> lowest()
 { return min(); }

 //! unit_pair types are unsigned
 static const bool is_signed = false;

 //! uint_pair types are integers
 static const bool is_integer = true;

 //! unit_pair types contain exact integers
 static const bool is_exact = true;

 //! unit_pair radix is binary
 static const int radix = 2;

 //! number of binary digits (bits) in uint_pair
 static const int digits = stxxl::uint_pair<HighType>::digits;

 //! epsilon is zero
 static const stxxl::uint_pair<HighType> epsilon()
 { return stxxl::uint_pair<HighType>(0, 0); }

 //! rounding error is zero
 static const stxxl::uint_pair<HighType> round_error()
 { return stxxl::uint_pair<HighType>(0, 0); }

 //! no exponent
 static const int min_exponent = 0;

 //! no exponent
 static const int min_exponent10 = 0;

 //! no exponent
 static const int max_exponent = 0;

 //! no exponent
 static const int max_exponent10 = 0;

 //! no infinity
 static const bool has_infinity = false;
};

} // namespace std

#endif // !STXXL_COMMON_UINT_TYPES_HEADER