Radix2IntegerScanner.h

//
//  Radix2IntegerScanner.h
//  libraries/shared/src
//
//  Created by Tobias Schwinger on 3/23/13.
//  Copyright 2013 High Fidelity, Inc.
//
//  Distributed under the Apache License, Version 2.0.
//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html
//
 
#ifndef hifi_Radix2IntegerScanner_h
#define hifi_Radix2IntegerScanner_h
 
#include <stddef.h>
#include <stdint.h>
 
namespace type_traits { // those are needed for the declaration, see below
 
    // Note: There are better / more generally appicable implementations 
    // in C++11, make_signed is missing in TR1 too - so I just use C++98
    // hacks that get the job done...
 
    template< typename T > struct is_signed 
    { static bool const value = T(-1) < T(0); };
 
    template< typename T, size_t S = sizeof(T) > struct make_unsigned;
    template< typename T > struct make_unsigned< T, 1 > { typedef uint8_t type; };
    template< typename T > struct make_unsigned< T, 2 > { typedef uint16_t type; };
    template< typename T > struct make_unsigned< T, 4 > { typedef uint32_t type; };
    template< typename T > struct make_unsigned< T, 8 > { typedef quint64 type; };
}
 
 
template< typename T, 
        bool _Signed = type_traits::is_signed<T>::value  >
class Radix2IntegerScanner;
 
 
 
template< typename UInt >
class Radix2IntegerScanner< UInt, false > {
 
        UInt valMsb;
    public:
 
        Radix2IntegerScanner()
            : valMsb(~UInt(0) &~ (~UInt(0) >> 1)) { }
 
        explicit Radix2IntegerScanner(int bits)
            : valMsb(UInt(1u) << (bits - 1)) {
        }
 
        typedef UInt state_type;
 
        state_type initial_state()  const   { return valMsb; }
        bool advance(state_type& s) const   { return (s >>= 1) != 0u; }
 
        bool bit(UInt const& v, state_type const& s) const { return !!(v & s); }
};
 
template< typename Int >
class Radix2IntegerScanner< Int, true >
{
        typename type_traits::make_unsigned<Int>::type valMsb;
    public:
 
        Radix2IntegerScanner()
            : valMsb(~state_type(0u) &~ (~state_type(0u) >> 1)) {
        }
 
        explicit Radix2IntegerScanner(int bits)
            : valMsb(state_type(1u) << (bits - 1)) {
        }
 
 
        typedef typename type_traits::make_unsigned<Int>::type state_type;
        
        state_type initial_state()  const   { return valMsb; }
        bool advance(state_type& s) const   { return (s >>= 1) != 0u; }
 
        bool bit(Int const& v, state_type const& s) const { return !!((v-valMsb) & s); }
};
 
#endif // hifi_Radix2IntegerScanner_h