17.2.10 Unsigned_Base_Range aspect ¶

A new pragma/aspect, Unsigned_Base_Range, is introduced to explicitly enforce the use of an unsigned base type for signed integer types. RM-3.5.4(9) mandates a symmetric base range for signed integer types. This requirement often requires the use of larger data types for arithmetic operations, potentially introducing undesirable run-time overhead and performance penalties, particularly in embedded systems. For instance, on a 64-bit architecture, a 64-bit multiplication can be performed with a single hardware instruction, whereas a 128-bit multiplication requires multiple instructions and intermediate steps.

Here is an example of this feature:

type Uns_64 is range 0 .. 2 ** 64 - 1
  with Size => 64,
       Unsigned_Base_Range => True;

It ensures that arithmetic operations of type Uns_64 are carried out using 64 bits.