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package work.Bit_Manipulation

This package contains miscellaneous bit mangling, err, manipulation functions:

• Bit Reversal:

  function bit_reverse
  (A : in std_ulogic_vector)
  return std_ulogic_vector;

  reverses the bits in A. Example:

  bit_reverse("1101000") => "0001011"

  The result type is std_ulogic_vector(A'length-1 downto 0).

• Bit Extraction:

  function bit_extract
  (A : in std_ulogic_vector;
   N : in positive;
   O : in natural := 0)
  return std_ulogic_vector;

  extracts every N'th bit from A, starting with bit O (counted from the right). Example:

  bit_extract("100100", 3, 2) => "11"

  The result type is std_ulogic_vector(X-1 downto 0)
  where X := (A'length + N - O - 1) / N.

• Bit Duplication:

  function bit_duplicate
  (A : in std_ulogic_vector;
   N : in positive)
  return std_ulogic_vector;

  duplicates A bitwise, N times. Example:

  bit_duplicate("101", 3) => "111000111"

  The result type is std_ulogic_vector(N*A'length-1 downto 0).

• Vector Duplication:

  function vector_duplicate
  (A : in std_ulogic_vector;
   N : in positive)
  return std_ulogic_vector;

  duplicates A as a whole, N times. Example:

  vector_duplicate("101", 3) => "101101101"

  The result type is std_ulogic_vector(N*A'length-1 downto 0).

• AND/OR Cascading:

  function cascade_and
  (A : in std_ulogic_vector)
  return std_ulogic_vector;

function cascade_or
  (A : in std_ulogic_vector)
  return std_ulogic_vector;

  perform AND and OR cascading operations, from right to left.

  

  The actual implementation is more efficient, however :-) Example:

  cascade_and("01100111") => "00000111"
cascade_or("01100111") => "01111111"

  The result type is std_ulogic_vector(A'length-1 downto 0).

• AND/OR/XOR Reducing:

  function reduce_and
  (A : in std_ulogic_vector)
  return std_ulogic;

function reduce_xor
  (A : in std_ulogic_vector)
  return std_ulogic;

function reduce_or
  (A : in std_ulogic_vector)
  return std_ulogic;

  perform the AND, OR and XOR operations, respectively, over all bits of A.

  The result type is std_ulogic.

• General Shift Functions:

  function lshift
  (A : in std_ulogic_vector;
   N : in natural;
   C : in std_ulogic)
  return std_ulogic_vector;

function rshift
  (A : in std_ulogic_vector;
   N : in natural;
   C : in std_ulogic)
  return std_ulogic_vector;

  perform the left/right shift operations. Shifted-in bits will have the value of C. Note that the N operand is not restricted to A'length. That is, if N >= A'length, all result bits will equal C.

  The result type is std_ulogic_vector(A'length-1 downto 0).

• Convenience Shift Functions:

  function lshift
  (A : in std_ulogic_vector;
   N : in natural)
  return std_ulogic_vector;

  is equivalent to lshift(A, N, '0').

  function lshifta
  (A : in std_ulogic_vector;
   N : in natural)
  return std_ulogic_vector;

  is equivalent to lshift(A, N, A(A'right)).

  function rshift
  (A : in std_ulogic_vector;
   N : in natural)
  return std_ulogic_vector;

  is equivalent to rshift(A, N, '0').

  function rshifta
  (A : in std_ulogic_vector;
   N : in natural)
  return std_ulogic_vector;

  is equivalent to rshift(A, N, A(A'left)).

• Rotate Functions:

  function lrotate
  (A : in std_ulogic_vector;
   N : in natural)
  return std_ulogic_vector;

function rrotate
  (A : in std_ulogic_vector;
   N : in natural)
  return std_ulogic_vector;

  rotate A left and right, respectively, by N mod A'length bits.

  The result type is std_ulogic_vector(A'length-1 downto 0).