Additional notes (March, 2026)

Assigned to SG6 at the request of the SG6 chair, via paper issue 2684.

The above resolution was approved by SG6 and EWG.

Proposed resolution (approved by CWG 2026-03-27):

Change in 5.13.4 [lex.fcon] paragraph 3 as follows:

If the scaled value is not in the range of representable values for its type, the program is ill-formed. Otherwise, the value of a floating-point-literal is the scaled value if representable, else the larger or smaller representable value nearest the scaled value, chosen in an implementation-defined manner.

[ Example:

The following example assumes that std::float32_t is supported (6.9.3 [basic.extended.fp]).

  std::float32_t x = 0.0f32;          // value 0 is exactly representable
  std::float32_t y = 0.1f32;          // rounded to one of two values nearest to 0.1
  std::float32_t z = 1e1000000000f32; // either greatest finite value or positive infinity

-- end example ]

(From submission #801.)

Implementations diverge on whether the following declaration is well-formed:

  float x = 1e100000000000000000000000000000000000000000000000.f;

However, 5.13.4 [lex.fcon] paragraph 3 seems to be clear that this is allowed if float has a representation of infinity.