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4153. Fix extra "-1" for philox_engine::max()

Section: 29.5.4.5 [rand.eng.philox] Status: Tentatively Ready Submitter: Ruslan Arutyunyan Opened: 2024-09-18 Last modified: 2024-10-02

Priority: Not Prioritized

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Discussion:

There is a typo in philox_engine wording that makes "-1" two times instead of one for max() method. The reason for that typo is that the wording was originally inspired by mersenne_twister_engine but after getting feedback that what is written in the philox_engine synopsis is not C++ code, the authors introduced the m variable (as in subtract_with_carry_engine) but forgot to remove "-1" in the m definition.

Note: after the proposed resolution below is applied the m variable could be reused in other places: basically in all places where the mod 2^w pattern appears (like subtract_with_carry_engine does). The authors don’t think it’s worth changing the rest of the wording to reuse the m variable. If somebody thinks otherwise, please provide such feedback.

[2024-10-02; Reflector poll]

Set status to Tentatively Ready after six votes in favour during reflector poll.

Proposed resolution:

This wording is relative to N4988.

1. Modify 29.5.4.5 [rand.eng.philox] as indicated:

   -1- A philox_engine random number engine produces unsigned integer random numbers in the closed interval [0, m]), where m = 2^w − 1 and the template parameter w defines the range of the produced numbers.