Algorithm for copying N bits at arbitrary position from one int to another

Question

An interesting problem I\'ve been pondering the past few days is how to copy one integer\'s bits into another integer at a given position in the destination integer. So, for exa

Answer 1

// SET OF FUNCTIONS

//##########    BIT - BIT   
template < typename var_t >     inline  var_t       bit_V           ( uint8_t b )                                               { return var_t(1) << b; }           // Same as usual macros, but this one converts de variable type, so that you can use it in uint8_t to uint64_t for example.
template < typename var_t >     inline  var_t       bit_get         ( const var_t & V , uint8_t b )                             { return V &    bit_V<var_t>(b); }  // Can be used as bool or to get the mask of the bit.
template < typename var_t >     inline  var_t       bit_settled     ( const var_t & V , uint8_t b )                             { return V |    bit_V<var_t>(b); } 
template < typename var_t >     inline  var_t       bit_unsettled   ( const var_t & V , uint8_t b )                             { return V &~   bit_V<var_t>(b); } 
template < typename var_t >     inline  void        bit_set         ( var_t & V , uint8_t b )                                   {        V |=   bit_V<var_t>(b); } 
template < typename var_t >     inline  void        bit_unset       ( var_t & V , uint8_t b )                                   {        V &=  ~bit_V<var_t>(b); } 
template < typename var_t >     inline  void        bit_mod         ( var_t & V , uint8_t b , bool set )                        { if (set) bit_set(V,b); else bit_unset(V,b); } //  compiler will optimize depending on if 'set' is constant.
template < typename var_t >     inline  void        bit_cpy         ( var_t & V , const var_t & S , uint8_t b )                 { var_t t = bit_get(S,b); V |= t; V &~ t; } 
template < typename var_t >     inline  void        bit_cpy         ( var_t & V , const var_t & S , uint8_t bV , uint8_t bM )   { bit_mod(V,bV,bit_get(S,bM)); } 
/// MULTIPLE BITS:
template < typename var_t >     inline  void        bits_set        ( var_t & V , const var_t & S )                                     { V |=  S;  }
template < typename var_t >     inline  void        bits_unset      ( var_t & V , const var_t & S )                                     { V &= ~S; }
/// ONLY WITH UNSIGNED INTS:    'at' parameters are refered to the less significant bit (lsb), starting at 0 index ( a byte would have 7 to 0 bits ).
template < typename var_t >             void        bits_cpy        ( var_t & V , const var_t & S , uint8_t numBits , uint8_t atlsb = 0  )  {   //  I choosed not to make this one inline
                                                                        var_t       mask = (~var_t(0)>>(sizeof(var_t)*8 - numBits))<<atlsb;
                                                                        bits_unset  ( V , mask ) ; 
                                                                        bits_set    ( V , S & mask  ) ; 
                                                                    }
template < typename var_t >             void        bits_cpy        ( var_t & V , const var_t & S , uint8_t numBits , uint8_t atVlsb , uint8_t atSlsb ) {   //  I choosed not to make this one inline
                                                                        bits_cpy ( V , (atVlsb>atSlsb)?(S<<(atVlsb-atSlsb)):(S>>(atSlsb-atVlsb)) , numBits , atVlsb ) ; 
                                                                    }
template < typename var_t >             var_t       bits_cpyd       ( const var_t & V , const var_t & S , uint8_t numBits , uint8_t atlsb = 0  )    { 
                                                                        var_t r = V;
                                                                        bits_cpy    (r,S,numBits,atlsb); 
                                                                        return r;
                                                                    }
template < typename var_t >             var_t       bits_cpyd       ( const var_t & V , const var_t & S , uint8_t numBits , uint8_t atVlsb , uint8_t atSlsb )   {   
                                                                        var_t r = V;
                                                                        bits_cpy    (r,S,numBits,atVlsb,atSlsb); 
                                                                        return r;
                                                                    }

//##########    BIT - BIT   - EXAMPLE OF USE WITH THE MOST RELEVANT FUNCTIONS:
// I used them inside functions, to get/set two variables inside a class, u and c

                void                u_set               ( edrfu_t u )       {           bits_cpy    <uint32_t>  ( CFG       , u         , 8     , 2             ,0              );}
                edrfu_t             u_get               ()                  { return    bits_cpyd   <uint32_t>  ( 0         , CFG       , 8     , 0             ,2              );}
                void                c_set               ( edrfc_t c )       {           bits_cpy    <uint32_t>  ( CFG       , c         , 2     );}
                edrfc_t             c_get               ()                  { return    bits_cpyd   <uint32_t>  ( 0         , CFG       , 2     );}