From Jason Turner

[lex.fcon]

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  ### Floating literals <a id="lex.fcon">[[lex.fcon]]</a>
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  ``` bnf
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  floating-literal:
 
 
 
 
 
 
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  fractional-constant exponent-partₒₚₜ floating-suffixₒₚₜ
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  digit-sequence exponent-part floating-suffixₒₚₜ
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  ```
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  ``` bnf
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  fractional-constant:
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  digit-sequenceₒₚₜ '.' digit-sequence
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  digit-sequence '.'
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  ```
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  ``` bnf
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  exponent-part:
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  'e' signₒₚₜ digit-sequence
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  'E' signₒₚₜ digit-sequence
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  ```
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  ``` bnf
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  sign: one of
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  '+ -'
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  ```
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@@ -32,25 +56,42 @@ digit-sequence:
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  ``` bnf
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  floating-suffix: one of
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  'f l F L'
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  ```
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- A floating literal consists of an integer part, a decimal point, a
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- fraction part, an `e` or `E`, an optionally signed integer exponent, and
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- an optional type suffix. The integer and fraction parts both consist of
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- a sequence of decimal (base ten) digits. Optional separating single
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- quotes in a *digit-sequence* are ignored when determining its value. The
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- literals `1.602'176'565e-19` and `1.602176565e-19` have the same value.
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- Either the integer part or the fraction part (not both) can be omitted;
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- either the decimal point or the letter `e` (or `E` ) and the exponent
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- (not both) can be omitted. The integer part, the optional decimal point
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- and the optional fraction part form the *significant part* of the
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- floating literal. The exponent, if present, indicates the power of 10 by
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- which the significant part is to be scaled. If the scaled value is in
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- the range of representable values for its type, the result is the scaled
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- value if representable, else the larger or smaller representable value
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- nearest the scaled value, chosen in an *implementation-defined* manner.
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- The type of a floating literal is `double` unless explicitly specified
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- by a suffix. The suffixes `f` and `F` specify `float`, the suffixes `l`
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- and `L` specify `long` `double`. If the scaled value is not in the range
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- of representable values for its type, the program is ill-formed.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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  ### Floating literals <a id="lex.fcon">[[lex.fcon]]</a>
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  ``` bnf
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  floating-literal:
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+ decimal-floating-literal
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+ hexadecimal-floating-literal
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+ ```
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+
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+ ``` bnf
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+ decimal-floating-literal:
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  fractional-constant exponent-partₒₚₜ floating-suffixₒₚₜ
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  digit-sequence exponent-part floating-suffixₒₚₜ
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  ```
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+ ``` bnf
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+ hexadecimal-floating-literal:
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+ hexadecimal-prefix hexadecimal-fractional-constant binary-exponent-part floating-suffixₒₚₜ
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+ hexadecimal-prefix hexadecimal-digit-sequence binary-exponent-part floating-suffixₒₚₜ
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+ ```
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+
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  ``` bnf
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  fractional-constant:
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  digit-sequenceₒₚₜ '.' digit-sequence
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  digit-sequence '.'
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  ```
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+ ``` bnf
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+ hexadecimal-fractional-constant:
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+ hexadecimal-digit-sequenceₒₚₜ '.' hexadecimal-digit-sequence
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+ hexadecimal-digit-sequence '.'
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+ ```
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+
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  ``` bnf
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  exponent-part:
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  'e' signₒₚₜ digit-sequence
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  'E' signₒₚₜ digit-sequence
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  ```
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+ ``` bnf
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+ binary-exponent-part:
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+ 'p' signₒₚₜ digit-sequence
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+ 'P' signₒₚₜ digit-sequence
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+ ```
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+
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  ``` bnf
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  sign: one of
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  '+ -'
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  ```
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  ``` bnf
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  floating-suffix: one of
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  'f l F L'
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  ```
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+ A floating literal consists of an optional prefix specifying a base, an
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+ integer part, a radix point, a fraction part, an `e`, `E`, `p` or `P`,
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+ an optionally signed integer exponent, and an optional type suffix. The
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+ integer and fraction parts both consist of a sequence of decimal (base
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+ ten) digits if there is no prefix, or hexadecimal (base sixteen) digits
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+ if the prefix is `0x` or `0X`. The floating literal is a *decimal
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+ floating literal* in the former case and a *hexadecimal floating
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+ literal* in the latter case. Optional separating single quotes in a
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+ *digit-sequence* or *hexadecimal-digit-sequence* are ignored when
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+ determining its value.
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+
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+ [*Example 1*: The floating literals `1.602'176'565e-19` and
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+ `1.602176565e-19` have the same value. — *end example*]
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+
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+ Either the integer part or the fraction part (not both) can be omitted.
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+ Either the radix point or the letter `e` or `E` and the exponent (not
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+ both) can be omitted from a decimal floating literal. The radix point
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+ (but not the exponent) can be omitted from a hexadecimal floating
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+ literal. The integer part, the optional radix point, and the optional
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+ fraction part, form the *significand* of the floating literal. In a
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+ decimal floating literal, the exponent, if present, indicates the power
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+ of 10 by which the significand is to be scaled. In a hexadecimal
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+ floating literal, the exponent indicates the power of 2 by which the
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+ significand is to be scaled.
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+
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+ [*Example 2*: The floating literals `49.625` and `0xC.68p+2` have the
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+ same value. — *end example*]
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+
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+ If the scaled value is in the range of representable values for its
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+ type, the result is the scaled value if representable, else the larger
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+ or smaller representable value nearest the scaled value, chosen in an
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+ *implementation-defined* manner. The type of a floating literal is
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+ `double` unless explicitly specified by a suffix. The suffixes `f` and
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+ `F` specify `float`, the suffixes `l` and `L` specify `long` `double`.
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+ If the scaled value is not in the range of representable values for its
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+ type, the program is ill-formed.
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