guideline

Represent numbers in a consistent fashion.

Represent literals in a radix appropriate to the problem.

Use underscores to separate digits the same way commas or periods (or spaces for nondecimal bases) would be used in normal text.

When using scientific notation, make the E consistently either uppercase or lowercase.

In an alternate base, represent the alphabetic characters in either all uppercase or all lowercase.

- Decimal and octal numbers are grouped by threes beginning on the left side of the radix point and by fives beginning on the right side of the radix point.
- The E is always capitalized in scientific notation.
- Use uppercase for the alphabetic characters representing digits in bases above 10.
- Hexadecimal numbers are grouped by fours beginning on either side of the radix point.

example

type Maximum_Samples     is range          1 ..  1_000_000;
type Legal_Hex_Address   is range   16#0000# ..   16#FFFF#;
type Legal_Octal_Address is range 8#000_000# .. 8#777_777#;
Avogadro_Number : constant := 6.02216_9E+23;

To represent the number 1/3 as a constant, use:

One_Third : constant := 1.0 / 3.0;

Avoid this use:

One_Third_As_Decimal_Approximation : constant := 0.33333_33333_3333;

or:

One_Third_Base_3 : constant := 3#0.1#;

rationale

Consistent use of uppercase or lowercase aids scanning for numbers. Underscores serve to group portions of numbers into familiar patterns. Consistency with common use in everyday contexts is a large part of readability.

notes

If a rational fraction is represented in a base in which it has a terminating rather than a repeating representation, as 3#0.1# does in the example above, it may have increased accuracy upon conversion to the machine base.