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## 6.14 Data Types in BP and GPC

- Integer types have different sizes in Borland and GNU Pascal:

  Borland Pascal | GNU Pascal | Bits (1) | Signed
  `ShortInt` | `ByteInt` | `8` | `yes`
  `Integer` | `ShortInt` | `16` | `yes`
  `LongInt` | `Integer` | `32` | `yes`
  `Comp` | `LongInt, Comp` | `64` | `yes`
  `Byte` | `Byte` | `8` | `no`
  `Word` | `ShortWord` | `16` | `no`
  n/a | `Word` | `32` | `no`
  n/a | `LongWord` | `64` | `no`

  (1) The size of the GNU Pascal types may depend on the platform. The sizes above apply to 32 bit platforms, including the IA32.

  If you care for types with exactly the same size as in Borland Pascal, take a look at the ``System'` unit and read its comments.

  You can get the size of a type with ``SizeOf'` in bytes (like in Borland Pascal) and with ``BitSizeOf'` in bits, and you can declare types with a specific size (given in bits), e.g.:

      program IntegerSizeDemo;
      type
        MyInt  = Integer (42);  { 42 bits, signed }
        MyWord = Word (2);      { 2 bits, unsigned, i.e., 0 .. 3 }
        MyCard = Cardinal (2);  { the same }

        HalfInt = Integer (BitSizeOf (Integer) div 2);
          { A signed integer type which is half as big as the normal
            `Integer' type, regardless of how big `Integer' is
            on any platform the program is compiled on. }

      begin
      end.

- Borland's real (floating point) types are supported except for the 6-byte software Real type (but the ``System'` unit provides conversion routines for it). GNU Pascals's ``Real'` type has 8 bytes on the IA32 and is the same as ``Double'`. In addition there are alternative names for real types:

  Borland Pascal | GNU Pascal
  `Single` | `Single, ShortReal`
  `Real` | n/a (1)
  `Double` | `Double, Real`
  `Extended` | `Extended, LongReal`
  `Comp` | `LongInt, Comp` (see above)

  (1) But see ``BPReal'`, ``RealToBPReal'` and ``BPRealToReal'` in GPC's `System` unit.

- Complex numbers: According to Extended Pascal, GNU Pascal has built-in complex numbers and supports a number of mathematical functions on them, e.g. ``Abs'`, ``Sqr'`, ``SqRt'`, ``Exp'`, ``Ln'`, ``Sin'`, ``Cos'`, ``ArcTan'`.

- Record types: GNU Pascal by default aligns 32-bit fields on 4-byte addresses because this improves performance. So, e.g., the record

      type
        MyRec = record
          f, o, oo: Boolean;
          Bar: Integer
        end;

  has 8 bytes, not 7. Use the `--pack-struct` option or declare the record as ``packed'` to force GPC to pack it to 7 bytes. However, note that this produces somewhat less efficient code on the IA32 and far less efficient code on certain other processors. Packing records and arrays is mostly useful only when using large structures where memory usage is a real concern, or when reading or writing them from/to binary files where the exact layout matters.

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This document was generated by Frank Heckenbach on May, 10 2002 using texi2html