The PIM system module (The GNU Modula-2 Compiler)

### 2.22 The PIM system module ¶

    DEFINITION MODULE SYSTEM ;

    EXPORT QUALIFIED BITSPERBYTE, BYTESPERWORD,
                     ADDRESS, WORD, BYTE, CSIZE_T, CSSIZE_T, COFF_T, CARDINAL64, (*
                     Target specific data types.  *)
                     ADR, TSIZE, ROTATE, SHIFT, THROW, TBITSIZE ;
                     (* SIZE is also exported if -fpim2 is used.  *)

    CONST
      BITSPERBYTE   = __ATTRIBUTE__ __BUILTIN__ ((BITS_PER_UNIT)) ;
      BYTESPERWORD  = __ATTRIBUTE__ __BUILTIN__ ((UNITS_PER_WORD)) ;

    (* Note that the full list of system and sized datatypes include:
       LOC, WORD, BYTE, ADDRESS,

       (and the non language standard target types)

       INTEGER8, INTEGER16, INTEGER32, INTEGER64,
       CARDINAL8, CARDINAL16, CARDINAL32, CARDINAL64,
       WORD16, WORD32, WORD64, BITSET8, BITSET16,
       BITSET32, REAL32, REAL64, REAL128, COMPLEX32,
       COMPLEX64, COMPLEX128, CSIZE_T, CSSIZE_T.

       Also note that the non-standard data types will
       move into another module in the future.  *)

    (* The following types are supported on this target:
    TYPE
       (* Target specific data types.  *)
    *)

    (*
       all the functions below are declared internally to gm2
       ======================================================

    PROCEDURE ADR (VAR v: <anytype>): ADDRESS;
      (* Returns the address of variable v. *)

    PROCEDURE SIZE (v: <type>) : ZType;
      (* Returns the number of BYTES used to store a v of
         any specified <type>.  Only available if -fpim2 is used.
      *)

    PROCEDURE TSIZE (<type>) : CARDINAL;
      (* Returns the number of BYTES used to store a value of the
         specified <type>.
      *)

    PROCEDURE ROTATE (val: <a set type>;
                      num: INTEGER): <type of first parameter>;
      (* Returns a bit sequence obtained from val by rotating up/right
         or down/right by the absolute value of num.  The direction is
         down/right if the sign of num is negative, otherwise the direction
         is up/left.
      *)

    PROCEDURE SHIFT (val: <a set type>;
                     num: INTEGER): <type of first parameter>;
      (* Returns a bit sequence obtained from val by shifting up/left
         or down/right by the absolute value of num, introducing
         zeros as necessary.  The direction is down/right if the sign of
         num is negative, otherwise the direction is up/left.
      *)

    PROCEDURE THROW (i: INTEGER) <* noreturn *> ;
      (*
         THROW is a GNU extension and was not part of the PIM or ISO
         standards.  It throws an exception which will be caught by the
         EXCEPT block (assuming it exists).  This is a compiler builtin
         function which interfaces to the GCC exception handling runtime
         system.
         GCC uses the term throw, hence the naming distinction between
         the GCC builtin and the Modula-2 runtime library procedure Raise.
         The later library procedure Raise will call SYSTEM.THROW after
         performing various housekeeping activities.
      *)

    PROCEDURE TBITSIZE (<type>) : CARDINAL ;
      (* Returns the minimum number of bits necessary to represent
         <type>.  This procedure function is only useful for determining
         the number of bits used for any type field within a packed RECORD.
         It is not particularly useful elsewhere since <type> might be
         optimized for speed, for example a BOOLEAN could occupy a WORD.
      *)
    *)

    (* The following procedures are invoked by GNU Modula-2 to
       shift non word sized set types. They are not strictly part
       of the core PIM Modula-2, however they are used
       to implement the SHIFT procedure defined above,
       which are in turn used by the Logitech compatible libraries.

       Users will access these procedures by using the procedure
       SHIFT above and GNU Modula-2 will map SHIFT onto one of
       the following procedures.
    *)

    (*
       ShiftVal - is a runtime procedure whose job is to implement
                  the SHIFT procedure of ISO SYSTEM. GNU Modula-2 will
                  inline a SHIFT of a single WORD sized set and will only
                  call this routine for larger sets.
    *)

    PROCEDURE ShiftVal (VAR s, d: ARRAY OF BITSET;
                        SetSizeInBits: CARDINAL;
                        ShiftCount: INTEGER) ;

    (*
       ShiftLeft - performs the shift left for a multi word set.
                   This procedure might be called by the back end of
                   GNU Modula-2 depending whether amount is known at
                   compile time.
    *)

    PROCEDURE ShiftLeft (VAR s, d: ARRAY OF BITSET;
                         SetSizeInBits: CARDINAL;
                         ShiftCount: CARDINAL) ;

    (*
       ShiftRight - performs the shift left for a multi word set.
                    This procedure might be called by the back end of
                    GNU Modula-2 depending whether amount is known at
                    compile time.
    *)

    PROCEDURE ShiftRight (VAR s, d: ARRAY OF BITSET;
                          SetSizeInBits: CARDINAL;
                          ShiftCount: CARDINAL) ;

    (*
       RotateVal - is a runtime procedure whose job is to implement
                   the ROTATE procedure of ISO SYSTEM. GNU Modula-2 will
                   inline a ROTATE of a single WORD (or less)
                   sized set and will only call this routine for larger
                   sets.
    *)

    PROCEDURE RotateVal (VAR s, d: ARRAY OF BITSET;
                         SetSizeInBits: CARDINAL;
                         RotateCount: INTEGER) ;

    (*
       RotateLeft - performs the rotate left for a multi word set.
                    This procedure might be called by the back end of
                    GNU Modula-2 depending whether amount is known at
                    compile time.
    *)

    PROCEDURE RotateLeft (VAR s, d: ARRAY OF BITSET;
                          SetSizeInBits: CARDINAL;
                          RotateCount: CARDINAL) ;

    (*
       RotateRight - performs the rotate right for a multi word set.
                     This procedure might be called by the back end of
                     GNU Modula-2 depending whether amount is known at
                     compile time.
    *)

    PROCEDURE RotateRight (VAR s, d: ARRAY OF BITSET;
                           SetSizeInBits: CARDINAL;
                           RotateCount: CARDINAL) ;

    END SYSTEM.

The different dialects of Modula-2 PIM-[234] and ISO Modula-2 declare the function `SIZE` in different places. PIM-[34] and ISO Modula-2 declare `SIZE` as a pervasive function (declared in the base module). PIM-2 defined `SIZE` in the `SYSTEM` module (as shown above).

GNU Modula-2 allows users to specify the dialect of Modula-2 by using the `-fiso` and `-fpim2` command line switches.

The data types `CSIZE_T`, `CSSIZE_T` and `COFF_T` are also exported from the `SYSTEM` module. The type `CSIZE_T` is unsigned and is mapped onto the target C data type `size_t` whereas the type `CSSIZE_T` is mapped onto the signed C data type `ssize_t`. The default size for the signed type `COFF_T` is the same as `CSSIZE_T` and this can be overridden by the `-fm2-file-offset-bits=` command line option.

It is anticipated that these should only be used to provide cross platform definition modules for C libraries.

There are also a variety of fixed sized `INTEGER` and `CARDINAL` types. The variety of the fixed sized types will depend upon the target architecture.