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2079. Required pow() overloads

Section: 29.7 [c.math] Status: NAD Submitter: Steve Clamage Opened: 2011-08-29 Last modified: 2016-01-28

Priority: 3

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Discussion:

LWG issue 550(i) removed the functions: 

float       pow(float, int);
double      pow(double, int);
long double pow(long double, int);

from header <cmath>. This change does not seem to be mentioned in Annex C, C.2.14.

Howard:

N3290 29.7 [c.math]/p11 says:

Moreover, there shall be additional overloads sufficient to ensure:

  1. If any argument corresponding to a double parameter has type long double, then all arguments corresponding to double parameters are effectively cast to long double.
  2. Otherwise, if any argument corresponding to a double parameter has type double or an integer type, then all arguments corresponding to double parameters are effectively cast to double.
  3. Otherwise, all arguments corresponding to double parameters are effectively cast to float.

From C99 7.12.7.4 we have: 

double pow(double, double);

29.7 [c.math]/p11/b2 says that if the client calls pow(2.0f, 2), then the int for second argument causes the following effective call to be made: 

pow(static_cast<double>(2.0f), static_cast<double>(2)) -> double

The first sentence of p11 implies that this is done by supplying the following additional overload: 

double pow(float, int);

If the client calls pow(2.0, 2), then the same reasoning (b2 again) implies the following additional overload: 

double pow(double, int);

If the client calls pow(2.0l, 2), then b1 implies the following additional overload: 

long double pow(long double, int);

In all, p11 implies hundreds (perhaps thousands?) of extra overloads. All but one of which is a superset of the overloads required by C++98/03 (that one being pow(float, int) which had its return type changed from float to double).

In practice, at least some vendors implement p11 by using templated overloads as opposed to ordinary overloads.

Steve Clamage:

Thanks. I didn't see that those extra overloads were actually implied by p11, despite the first sentence. Without examples, the point is a bit subtle (at least for me).

[2015-05-05 Lenexa: Move to NAD]

Billy: I believe this is NAD.

STL: Oh, Steve himself agrees.

Wakely: The issue marked as NAD will be sufficient.

STL: Yes, we should get rid of this.

Billy: I don't see any minutes from Issaquah.

Marshall: Since Steve agrees, does anyone object to marking as NAD?

Nope.

Proposed resolution: