[Bug libstdc++/43660] range of random-number generator seems wrong/confusing

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43660

--- Comment #5 from Jonathan Wakely redi at gcc dot gnu.org ---
(In reply to Jonathan Wakely from comment #2)
 (In reply to comment #0)
  [Note that the same issue exists with other ways of invoking using the
  generator (e.g., a std::uniform_real_distributionfloat with bounds of
  0 and 1 will indeed return 1); but it's less clear its a bug in those
  cases (although, for instance, boost's random implementation never
  seems to return the upper bound).]
 
 Again, referring to the latest draft:
 A uniform_real_distribution random number distribution produces random
 numbers x, a = x  b
 
 So that does appear to be a bug

PR 64351 deals with that case.

[Bug libstdc++/43660] range of random-number generator seems wrong/confusing

[redi at gcc dot gnu dot org]

--- Comment #1 from redi at gcc dot gnu dot org  2010-04-06 10:38 ---
n1933 is ancient history, the RNG pieces have changed significantly

In the current draft it says:
A uniform_int_distribution random number distribution produces random integers
i, a = i = b

So it is a closed interval [a,b] rather than [a,b)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43660

[Bug libstdc++/43660] range of random-number generator seems wrong/confusing

[redi at gcc dot gnu dot org]

--- Comment #2 from redi at gcc dot gnu dot org  2010-04-06 10:40 ---
(In reply to comment #0)
 [Note that the same issue exists with other ways of invoking using the
 generator (e.g., a std::uniform_real_distributionfloat with bounds of
 0 and 1 will indeed return 1); but it's less clear its a bug in those
 cases (although, for instance, boost's random implementation never
 seems to return the upper bound).]

Again, referring to the latest draft:
A uniform_real_distribution random number distribution produces random numbers
x, a = x  b

So that does appear to be a bug


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43660

[Bug libstdc++/43660] range of random-number generator seems wrong/confusing

[redi at gcc dot gnu dot org]

--- Comment #3 from redi at gcc dot gnu dot org  2010-04-06 10:53 ---
(In reply to comment #0)
 
 As best as I can tell, std::random_shuffle wants its random-number
 generating functor to return results in the range [0,N), where N is the
 parameter it passes to the functor; i.e., the upper-bound is exclusive
 (and the lower-bound inclusive).

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3056.pdf changes the
third random_shuffle overload to shuffle and changes the requirements


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43660

[Bug libstdc++/43660] range of random-number generator seems wrong/confusing

[paolo dot carlini at oracle dot com]

--- Comment #4 from paolo dot carlini at oracle dot com  2010-04-06 11:00 
---
Jon is right and recently I removed that old comment from random.h because
indeed was incorrect.


-- 

paolo dot carlini at oracle dot com changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43660