[Boost-bugs] [Boost C++ Libraries] #10985: Logically dead code; dubious source code comment / inverted if condition?

Subject: [Boost-bugs] [Boost C++ Libraries] #10985: Logically dead code; dubious source code comment / inverted if condition?
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-01-30 21:10:57

#10985: Logically dead code; dubious source code comment / inverted if condition?
--------------------------------------+-------------------------
 Reporter:  Jonas Maaskola <jonas@…>  |      Owner:  johnmaddock
     Type:  Bugs                      |     Status:  new
Milestone:  To Be Determined          |  Component:  math
  Version:  Boost 1.57.0              |   Severity:  Problem
 Keywords:                            |
--------------------------------------+-------------------------
 Static code analysis with Coverity pointed me to some dead code in the
 function ibeta_imp in boost/math/special_functions/beta.hpp.
 My system's boost library is 1.55.0, but the issue is present identically
 in boost 1.57.
 In a block guarded by
 {{{
 if (normalised) {
 }}}
 there is the following line (number 1224):
 {{{
                fract -= (normalised ? 1 : boost::math::beta(a, b, pol));
 }}}
 Clearly, normalised has to be true due to the if guard thus the second
 part (boost::math::beta(a, b, pos)) will never be used.

 Furthermore, it may be that the if guard's condition is missing a negation
 for which there are two indications:
  * in the vicinity (i.e. in the function ibeta_imp) most other if
 statements (6 of 7) that involve normalised check if normalised is not set
 (i.e. "if(!normalised)"), and
  * more importantly, the first comment in that block on lines 1211-1213
 reads:
 {{{
 1209:         else if(normalised)
 1210:         {
 1211:            // the formula here for the non-normalised case is tricky
 to figure
 1212:            // out (for me!!), and requires two pochhammer
 calculations rather
 1213:            // than one, so leave it for now....
 }}}
 I apologize for my limited understanding of the details of the code, which
 precludes me from proposing a fix, but something seems fishy here!

 Finally, the line subsequent to the one with the dead code, i.e. line
 1225, contains a commented-out alternative. This indicates to me that this
 entire block may not have been fully satisfactory to the original
 author(s).

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/10985>
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