Merge pull request #42 from msoeken/shrink

Shrink truth tables.

Author: msoeken

docs/changelog.rst

@@ -7,6 +7,9 @@ v0.4 (not yet released)
 * Constructors: ``create_from_clauses``, ``create_characteristic``
   `#41 <https://github.com/msoeken/kitty/pull/41>`_
 
+* Operations: ``shrink_to``
+  `#42 <https://github.com/msoeken/kitty/pull/42>`_
+
 * CNF generation: ``cnf_characteristic``
   `#41 <https://github.com/msoeken/kitty/pull/41>`_
 

docs/operations.rst

@@ -37,6 +37,7 @@ Combination and manipulation
    min_base_inplace
    expand_inplace
    extend_to
+   shrink_to
    shift_left_inplace
    shift_left
    shift_right_inplace

include/kitty/operations.hpp

@@ -60,6 +60,7 @@ inline TT unary_not_if( const TT& tt, bool cond )
 
 /*! \brief Bitwise AND of two truth tables */
 template<typename TT>
+
 inline TT binary_and( const TT& first, const TT& second )
 {
   return binary_operation( first, second, std::bit_and<>() );
@@ -700,7 +701,7 @@ void extend_to( TT& tt, const TTFrom& from )
 
 /*! \brief Extends smaller truth table to larger static one
 
-  This is a special version of extend_to that has the truth table as a return
+  This is a special version of `extend_to` that has the truth table as a return
   value.  It only works for creating static truth tables.  The template
   parameter `NumVars` must be equal or larger to the number of variables in
   `from`.
@@ -715,6 +716,45 @@ inline static_truth_table<NumVars> extend_to( const TTFrom& from )
   return tt;
 }
 
+/*! \brief Shrinks larger truth table to smaller one
+
+  The function expects that the most significant bits, which are cut off, are
+  not in the functional support of the original function.  Only then it is 
+  ensured that the resulting function is equivalent. 
+
+  \param tt Smaller truth table to create
+  \param from Larger truth table to copy from
+*/
+template<typename TT, typename TTFrom>
+void shrink_to( TT& tt, const TTFrom& from )
+{
+  assert( tt.num_vars() <= from.num_vars() );
+
+  std::copy( from.begin(), from.begin() + tt.num_blocks(), tt.begin() );
+  
+  if ( tt.num_vars() < 6 )
+  {
+    tt.mask_bits();
+  }
+}
+
+/*! \brief Shrinks larger truth table to smaller static one
+
+  This is a special version of `shrink_to` that has the truth table as a return
+  value.  It only works for creating static truth tables.  The template
+  parameter `NumVars` must be equal or smaller to the number of variables in
+  `from`.
+
+  \param from Smaller truth table to copy from
+*/
+template<int NumVars, typename TTFrom>
+inline static_truth_table<NumVars> shrink_to( const TTFrom& from )
+{
+  static_truth_table<NumVars> tt;
+  shrink_to( tt, from );
+  return tt;
+}
+
 /*! \brief Left-shift truth table
 
   Drops overflowing most-significant bits and fills up least-significant bits

test/operations.cpp

@@ -494,6 +494,21 @@ TEST_F( OperationsTest, extend_to_same )
   EXPECT_EQ( tt1, tt2 );
 }
 
+TEST_F( OperationsTest, shrink_to )
+{
+  EXPECT_EQ( shrink_to<2>( from_hex<3>( "aa" ) ), from_hex<2>( "a" ) );
+  EXPECT_EQ( shrink_to<2>( from_hex<3>( "1a" ) ), from_hex<2>( "a" ) );
+  EXPECT_EQ( shrink_to<2>( from_hex<2>( "8" ) ), from_hex<2>( "8" ) );
+
+  EXPECT_EQ( shrink_to<5>( from_hex<7>( "cafecafecafecafecafecafecafecafe" ) ), from_hex<5>( "cafecafe") );
+
+  EXPECT_EQ( shrink_to<2>( from_hex( 3, "aa" ) ), from_hex<2>( "a" ) );
+  EXPECT_EQ( shrink_to<2>( from_hex( 3, "1a" ) ), from_hex<2>( "a" ) );
+  EXPECT_EQ( shrink_to<2>( from_hex( 2, "8" ) ), from_hex<2>( "8" ) );
+
+  EXPECT_EQ( shrink_to<5>( from_hex( 7, "cafecafecafecafecafecafecafecafe" ) ), from_hex<5>( "cafecafe") );
+}
+
 TEST_F( OperationsTest, shift_left )
 {
   EXPECT_EQ( shift_left( from_hex<3>( "e8"), 1 ), from_hex<3>( "d0" ) );