std.bitmanip - D Programming Language - Digital Mars

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Last update Wed Sep 2 00:11:52 2009

# std.bitmanip

Bit-level manipulation facilities.

Authors:
Walter Bright, Andrei Alexandrescu

template bitfields(T...)
  Allows creating bit fields inside structs and classes.

  Example:

      struct A
      {
          int a;
          mixin(bitfields!(
              uint, "x",    2,
              int,  "y",    3,
              uint, "z",    2,
              bool, "flag", 1));
      }
      A obj;
      obj.x = 2;
      obj.z = obj.x;

  The example above creates a bitfield pack of eight bits, which fit in one ubyte. The bitfields are allocated starting from the least significant bit, i.e. x occupies the two least significant bits of the bitfields storage.

  The sum of all bit lengths in one bitfield instantiation must be exactly 8, 16, 32, or 64. If padding is needed, just allocate one bitfield with an empty name.

  Example:

      struct A
      {
          mixin(bitfields!(
              bool, "flag1",    1,
              bool, "flag2",    1,
              uint, "",         6));
      }

  The type of a bit field can be any integral type or enumerated type. The most efficient type to store in bitfields is bool, followed by unsigned types, followed by signed types.

struct FloatRep;
  Allows manipulating the fraction, exponent, and sign parts of a float separately. The definition is:

      struct FloatRep
      {
          union
          {
              float value;
              mixin(bitfields!(
                        uint,  "fraction", 23,
                        ubyte, "exponent",  8,
                        bool,  "sign",      1));
          }
          enum uint bias = 127, fractionBits = 23, exponentBits = 8, signBits = 1;
      }

struct DoubleRep;
  Allows manipulating the fraction, exponent, and sign parts of a double separately. The definition is:

      struct DoubleRep
      {
          union
          {
              double value;
              mixin(bitfields!(
                        ulong,   "fraction", 52,
                        ushort,  "exponent", 11,
                        bool,    "sign",      1));
          }
          enum uint bias = 1023, signBits = 1, fractionBits = 52, exponentBits = 11;
      }

struct BitArray;
  An array of bits.

  const bool opIndex(size_t i);
  bool opIndexAssign(bool b, size_t i);
    Support for [index] operation for BitArray.

  BitArray dup();
    Support for array.dup property for BitArray.

  int opApply(int delegate(ref bool) dg);
  int opApply(int delegate(ref uint, ref bool) dg);
    Support for foreach loops for BitArray.

  BitArray reverse();
    Support for array.reverse property for BitArray.

  BitArray sort();
    Support for array.sort property for BitArray.

  bool opEquals(BitArray a2);
    Support for operators == and != for bit arrays.

  int opCmp(BitArray a2);
    Implement comparison operators.

  void init(bool[] ba);
    Set BitArray to contents of ba[]

  void init(void[] v, size_t numbits);
    Map BitArray onto v[], with numbits being the number of bits in the array. Does not copy the data.

    This is the inverse of opCast.

  void[] opCast();
    Convert to void[].

  BitArray opCom();
    Support for unary operator ~ for bit arrays.

  BitArray opAnd(BitArray e2);
    Support for binary operator & for bit arrays.

  BitArray opOr(BitArray e2);
    Support for binary operator | for bit arrays.

  BitArray opXor(BitArray e2);
    Support for binary operator ^ for bit arrays.

  BitArray opSub(BitArray e2);
    Support for binary operator - for bit arrays.

    a - b for BitArrays means the same thing as a & ~b.

  BitArray opAndAssign(BitArray e2);
    Support for operator &= bit arrays.

  BitArray opOrAssign(BitArray e2);
    Support for operator |= for bit arrays.

  BitArray opXorAssign(BitArray e2);
    Support for operator ^= for bit arrays.

  BitArray opSubAssign(BitArray e2);
    Support for operator -= for bit arrays.

    a -= b for BitArrays means the same thing as a &= ~b.

  BitArray opCatAssign(bool b);
  BitArray opCatAssign(BitArray b);
    Support for operator ~= for bit arrays.

  BitArray opCat(bool b);
  BitArray opCat_r(bool b);
  BitArray opCat(BitArray b);
    Support for binary operator ~ for bit arrays.

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