Bit16

The predefined data type bit16 is a subrange, 0..65535, that is stored in 16 bits. bit16 is a unique HP Pascal type because arithmetic operations on bit16 data are truncated to modulo 65535 when stored.

To determine if a type T is assignment compatible with bit16, treat bit16 as a subrange of integer:

If variable v is of type T and variable b16 is of type bit16, then the assignment b16 := v is legal if the value of v is within the range 0..65535.
If the ranges of T and bit16 do not overlap, the assignment b16 := v causes a compile-time error.
If the ranges of T and bit16 do overlap, but the value of v is outside the range of bit16, then the assignment b16 := v causes a run-time error.

Example

PROGRAM prog;
 
TYPE
   T1 = integer;     {overlaps bit16 range        }
   T2 = -32768..-1;  {does not overlap bit16 range}
   T3 = 0..65535;    {overlaps bit16 range        }
 
VAR
   v1 : T1;  {b16:=v1 may be legal, depending on value of v1}
   v2 : T2;  {b16:=v2 is never legal}
   v3 : T3;  {b16:=v3 is always legal}
  b16 : bit16;
 
BEGIN {prog}
   v1  := 65535;
   b16 := v1;       {legal}
   b16 := b16 + 5;  {legal; now b16 = (65540 MOD 65535) = 4}
   b16 := b16 - 5;  {legal; now b16 = 65535}
 
   v3 := 65535;
   v3 := v3 + 4;    {causes run-time error}
   v3 := 4;
   v3 := v3 - 5;    {causes run-time error}
 
   v1  := -20;
   b16 := v1;       {causes run-time error}
 
   v2  := -30;
   b16 := v2;       {causes compile-time error}
END. {prog}

Bit16

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