HP 3000 Manuals

HP Pascal/iX Programmer's Guide

Bit52 

The predefined data type bit52 is a subrange, 0..252-1, that is stored in
64 bits.  bit52 is a unique HP Pascal type because arithmetic operations
on bit52 data are performed as unsigned 64-bit integers.  Unsigned
addition and subtraction do not overflow.[REV BEG] Unsigned multiply may
overflow.  The compiler option OVFLCHECK has no effect.

Note that there are no bit52 constants in the compiler.  Therefore,
numbers in the range maxint + 1..252 -1 can not be expressed directly.
The function hex can be used with the compiler options TYPE_COERCION and
RANGE to fill part of this range.[REV END] The compiler option
TYPE_COERCION is also needed when initializing a bit52 constant field.
In this case, bit52() is not used.  When bit52 is used in an executable
statement, RANGE OFF must be used.

For number in the range of 232..252-1, a run-time computation must be
done.  If the numbers are all constants, they must be type coerced to
bit52 so they do not integer overflow.

Variant records can also be used to build up these large constants.

To determine if a type T is assignment compatible with bit52.

   *   If variable v is of type T and variable b52 is of type bit52, then
       the assignment b52 := v is legal if the value of v is within the
       range 0..252-1.

   *   If the ranges of T and bit52 do not overlap, the assignment b52 :=
       v causes a compile-time error.

   *   If the ranges of T and bit52 do overlap, but the value of v is
       outside the range of bit52, then the assignment b52 := v causes a
       run-time error.

Example 

     $standard_level 'hp_modcal'$
     program prog_bit52(output);

     var i : integer;
         b : bit52;

     type rec = record
                f1 : bit52;
                end;
     $push; type_coercion 'conversion'$
     const v_rec = rec[f1: hex('ffffffff')];      { bit52 constant field }
     $pop$
     begin
     b := hex('ffffffff');   { compile-time error }
     i := -1;

     try
     b := i;                 { run-time error }
     recover ;

(Example is continued on next page.)

     $push; type_coercion 'conversion'; range off$
     b := bit52(i) + 1;      { zero is stored }

     b := bit52(hex('ffffffff'));
     $pop$

     try
     i := b;                 { run-time error }
     recover ;

     try
     i := b + i;             { b and i are converted to longint and are }
                             { too big to fit back into i }
     recover ;

     i := hex('ffffffff');   { both b and i now have all bits on }

     { the following never prints since i is sign extended to longint and
       b is zero extended to longint }
     $push; type_coercion 'conversion'$
     if longint(i) = b then writeln('equal');
     $pop$
     end.

MPE/iX 5.0 Documentation