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2688. clamp misses preconditions and has extraneous condition on result

Section: 26.8.10 [alg.clamp] Status: C++17 Submitter: Martin Moene Opened: 2016-03-23 Last modified: 2017-07-30

Priority: 0

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Discussion:

In Jacksonville (2016), P0025R0 was voted in instead of the intended P0025R1. This report contains the necessary mending along with two other improvements.

This report:

• adds the precondition that misses from P0025R0 but is in P0025R1,

• corrects the returns: specification that contains an extraneous condition,

• replaces the now superfluous remark with a note on usage of clamp with float or double.

Thanks to Carlo Assink and David Gaarenstroom for making us aware of the extraneous condition in the returns: specification and for suggesting the fix and to Jeffrey Yasskin for suggesting to add a note like p3.

Previous resolution [SUPERSEDED]:

1. Edit 26.8.10 [alg.clamp] as indicated:

   template<class T>
     constexpr const T& clamp(const T& v, const T& lo, const T& hi);
   template<class T, class Compare>
     constexpr const T& clamp(const T& v, const T& lo, const T& hi, Compare comp);
   

   -1- Requires: The value of lo shall be no greater than hi. For the first form, type T shall be LessThanComparable (Table 18).

   -2- Returns: lo if v is less than lo, hi if hi is less than v, otherwise vThe larger value of v and lo if v is smaller than hi, otherwise the smaller value of v and hi.

   -3- NoteRemarks: If NaN is avoided, T can be float or doubleReturns the first argument when it is equivalent to one of the boundary arguments.

   -4- Complexity: At most two comparisons.

[2016-05 Issues Telecon]

Reworded p3 slightly.

Proposed resolution:

This wording is relative to N4582.

1. Edit 26.8.10 [alg.clamp] as indicated:

   template<class T>
     constexpr const T& clamp(const T& v, const T& lo, const T& hi);
   template<class T, class Compare>
     constexpr const T& clamp(const T& v, const T& lo, const T& hi, Compare comp);
   

   -1- Requires: The value of lo shall be no greater than hi. For the first form, type T shall be LessThanComparable (Table 18).

   -2- Returns: lo if v is less than lo, hi if hi is less than v, otherwise vThe larger value of v and lo if v is smaller than hi, otherwise the smaller value of v and hi.

   -3- NoteRemarks: If NaN is avoided, T can be a floating point type Returns the first argument when it is equivalent to one of the boundary arguments.

   -4- Complexity: At most two comparisons.