• d-bugmail puremagic.com (33/33) Mar 04 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7646
• d-bugmail puremagic.com (11/19) Mar 04 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7646
• d-bugmail puremagic.com (8/8) Mar 05 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7646
• d-bugmail puremagic.com (9/9) Mar 11 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7646
• d-bugmail puremagic.com (12/12) Jun 04 2012 http://d.puremagic.com/issues/show_bug.cgi?id=7646

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=7646

           Summary: bug in code sample and unittest
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: trivial
          Priority: P2
         Component: websites
        AssignedTo: nobody puremagic.com
        ReportedBy: josvanuden gmail.com


--- Comment #0 from josvanuden gmail.com 2012-03-04 11:59:48 PST ---
The following sample code on std.functional contains a bug.
http://dlang.org/phobos/std_functional.html#memoize

    ulong fib(ulong n) { 
        alias memoize!fib mfib; 
        return n < 2 ? 1 : mfib(n - 2) + mfib(n - 1); 
    } 

    assert(fib(10) == 89);

fib(10) should be 55. 
http://en.wikipedia.org/wiki/Fibonacci_number#List_of_Fibonacci_numbers

I think the code should be (n <= 2):

    ulong fib(ulong n) { 
        alias memoize!fib mfib; 
        return n <= 2 ? 1 : mfib(n - 2) + mfib(n - 1); 
    }

    assert(fib(10) == 55); 

It's also in the unittest
https://github.com/D-Programming-Language/phobos/blob/master/std/functional.d

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d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=7646



--- Comment #1 from josvanuden gmail.com 2012-03-04 12:08:27 PST ---
(In reply to comment #0)
 I think the code should be (n <= 2):
 
     ulong fib(ulong n) { 
         alias memoize!fib mfib; 
         return n <= 2 ? 1 : mfib(n - 2) + mfib(n - 1); 
     }
 
     assert(fib(10) == 55); 

No, that still won't do. This is better:

    ulong fib(ulong n) { 
        alias memoize!fib mfib; 
        return n <= 2 ? n != 0 : mfib(n - 2) + mfib(n - 1); 
    }

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d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=7646


josvanuden gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P2                          |P5


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d-bugmail puremagic.com writes:

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--- Comment #2 from josvanuden gmail.com 2012-03-11 04:24:44 PDT ---
ulong fib (ulong n) { 
    alias memoize!fib mfib; 
    return n < 2 ? n : mfib(n - 2) + mfib(n - 1); 
}

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d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=7646


josvanuden gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID


--- Comment #3 from josvanuden gmail.com 2012-06-04 07:16:19 PDT ---
It turns out some people regard F0 = 0 and some F0 = 1. So it's not a bug after
all.

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