[Boost-commit] svn:boost r83060 - in trunk: boost/multiprecision/cpp_int libs/multiprecision/doc libs/multiprecision/test

Subject: [Boost-commit] svn:boost r83060 - in trunk: boost/multiprecision/cpp_int libs/multiprecision/doc libs/multiprecision/test
From: john_at_[hidden]
Date: 2013-02-21 08:05:43

Author: johnmaddock
Date: 2013-02-21 08:05:41 EST (Thu, 21 Feb 2013)
New Revision: 83060
URL: http://svn.boost.org/trac/boost/changeset/83060

Log:
Fix sign of division in cpp_int when the values are small enough to fit in a double_limb_type.
Add test cases for above.
Fixes #8126.
Text files modified: 
   trunk/boost/multiprecision/cpp_int/divide.hpp    |     6 ++++++                                  
   trunk/libs/multiprecision/doc/multiprecision.qbk |     2 ++                                      
   trunk/libs/multiprecision/test/test_cpp_int.cpp  |    19 +++++++++++++++++++                     
   3 files changed, 27 insertions(+), 0 deletions(-)

Modified: trunk/boost/multiprecision/cpp_int/divide.hpp
==============================================================================
--- trunk/boost/multiprecision/cpp_int/divide.hpp	(original)
+++ trunk/boost/multiprecision/cpp_int/divide.hpp	2013-02-21 08:05:41 EST (Thu, 21 Feb 2013)
@@ -114,7 +114,10 @@
    if(r_order == 0)
    {
       if(result)
+      {
          *result = px[0] / py[0];
+         result->sign(x.sign() != y.sign());
+      }
       r = px[0] % py[0];
       return;
    }
@@ -126,7 +129,10 @@
          (static_cast<double_limb_type>(py[1]) << CppInt1::limb_bits) | py[0] 
          : py[0];
       if(result)
+      {
          *result = a / b;
+         result->sign(x.sign() != y.sign());
+      }
       r = a % b;
       return;
    }

Modified: trunk/libs/multiprecision/doc/multiprecision.qbk
==============================================================================
--- trunk/libs/multiprecision/doc/multiprecision.qbk	(original)
+++ trunk/libs/multiprecision/doc/multiprecision.qbk	2013-02-21 08:05:41 EST (Thu, 21 Feb 2013)
@@ -3617,6 +3617,8 @@
 * [*Breaking change] renamed `rational_adapter` to `rational_adaptor`.
 * Add support for [mpfi].
 * Add logged_adaptor.
+* Fix bug in integer division that results in incorrect sign of `cpp_int` when both arguments are small enough
+to fit in a `double_limb_type`.  See [@https://svn.boost.org/trac/boost/ticket/8126 8126].
 
 [h4 1.53]
 

Modified: trunk/libs/multiprecision/test/test_cpp_int.cpp
==============================================================================
--- trunk/libs/multiprecision/test/test_cpp_int.cpp	(original)
+++ trunk/libs/multiprecision/test/test_cpp_int.cpp	2013-02-21 08:05:41 EST (Thu, 21 Feb 2013)
@@ -470,6 +470,25 @@
          }
 
       }
+      //
+      // Specific bug report tests come last:
+      //
+      // Bug https://svn.boost.org/trac/boost/ticket/8126:
+      test_type a("-4294967296");
+      test_type b("4294967296");
+      test_type c("-1");
+      a = (a / b);
+      BOOST_CHECK_EQUAL(a, -1);
+      a = -4294967296;
+      a = (a / b) * c;
+      BOOST_CHECK_EQUAL(a, 1);
+      a = -23;
+      b = 23;
+      a = (a / b) * c;
+      BOOST_CHECK_EQUAL(a, 1);
+      a = -23;
+      a = (a / b) / c;
+      BOOST_CHECK_EQUAL(a, 1);
    }
 };