Real constants can either be decimal or hexadecimal numbers. They may have an optional leading plus or minus sign. The components of a real constant are the integer part, a mantissa, and an exponent used to represent scientific notation.

['+' | '-' ]   Integer  ['.'  [Mantissa  [Exponent]]]

['+' | '-' ]  [Integer]  '.'   Mantissa  [Exponent]

Real Decimal Constant

The integer part and the mantissa consist of decimal digits and underscores. The integer part cannot have a leading underscore. All numeric constants cannot end with an underscore.

A decimal exponent begins with the letter 'E' or 'e' followed by an optional sign and a series of digits and underscores. The exponent multiplies the value by 10 to the power of the exponent.

Decimal.Real := ['+' | '-']  (Decimal.Part  ['.'  Real.Part])  |  ('.'  Real.Part)

Decimal.Part := Digit  [( Digit | '_')  Digit

Real.Part    := Decimal.Part  [{'E' | 'e'}  ['+' | '-']  Decimal.Part]

Digit        := '0' to '9'

Real Hexadecimal Constant

Real hexadecimal constants are used to generate a precise binary real value. The integer part and the mantissa consist of hexadecimal digits and underscores. The integer part cannot have a leading underscore and again, all numeric constants cannot end with an underscore.

A hexadecimal exponent begins with the letter 'E' or 'e' followed by an optional sign and a series of digits and underscores. The exponent multiplies the value by 2 to the power of the exponent.

Hex.Real     := ['+' | '-']  '#'  { (Hex.Number  ['.'  Hex.Exponent])  
                                               | ('.'  Hex.Exponent) }

Hex.Exponent := Hex.Number  [{'P' | 'p'}  ['+' | '-']  Hex.Number]

Hex.Number   := Hex.Digit  [( Hex.Digit | '_')  Hex.Digit

Hex.Digit    := '0' to '9' | 'A' to 'F' | 'a' to 'f'