Movatterモバイル変換

Proposed resolution (June, 2018):

Change 9.8.1 [dcl.enum] paragraph 8 as follows:

b_max is the smallest value greater than orequal tomax(|e_min| -K,|e_max|),e_max) and equal to2^M - 1, whereM is a non-negativeinteger.

[Accepted as a DR at the November, 2018 (San Diego) meeting.]

According to 9.8.1 [dcl.enum] paragraph 7,

For an enumeration whose underlying type is fixed, the values of theenumeration are the values of the underlying type. Otherwise,for an enumeration wheree_min is the smallestenumerator ande_max is the largest, the values ofthe enumeration are the values in the rangeb_min tob_max, defined as follows: LetK be 1 for atwo's complement representation and 0 for a one's complement orsign-magnitude representation.b_max is the smallestvalue greater than or equal tomax(|e_min|-K,|e_max|) andequal to 2^M-1, whereM is a non-negativeinteger.b_min is zero ife_min isnon-negative and -(b_max+K) otherwise. Thesize of the smallest bit-field large enough to hold all the values ofthe enumeration type is max(M,1) ifb_min iszero andM+1 otherwise.

The result of these calculations is that the number of bitsrequired for

  enum { N = -1, Z = 0 }

is 1, but the number required for

  enum { N = -1 }

is 2. This is surprising. This could be fixed by changing|e_max| toe_max.