From 3111e690846bd95b8d03e1206cab2208a135e121 Mon Sep 17 00:00:00 2001
From: John Maddock <john@johnmaddock.co.uk>
Date: Thu, 21 Feb 2013 13:05:41 +0000
Subject: [PATCH] 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.

[SVN r83060]
---
 doc/multiprecision.qbk                        |  2 ++
 .../boost/multiprecision/cpp_int/divide.hpp   |  6 ++++++
 test/test_cpp_int.cpp                         | 19 +++++++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/doc/multiprecision.qbk b/doc/multiprecision.qbk
index b8806959..cb68d280 100644
--- a/doc/multiprecision.qbk
+++ b/doc/multiprecision.qbk
@@ -3617,6 +3617,8 @@ Windows Vista machine.
 * [*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]
 
diff --git a/include/boost/multiprecision/cpp_int/divide.hpp b/include/boost/multiprecision/cpp_int/divide.hpp
index 793fe0d9..21c973d3 100644
--- a/include/boost/multiprecision/cpp_int/divide.hpp
+++ b/include/boost/multiprecision/cpp_int/divide.hpp
@@ -114,7 +114,10 @@ void divide_unsigned_helper(
    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 @@ void divide_unsigned_helper(
          (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;
    }
diff --git a/test/test_cpp_int.cpp b/test/test_cpp_int.cpp
index fee9686c..79e8cce7 100644
--- a/test/test_cpp_int.cpp
+++ b/test/test_cpp_int.cpp
@@ -470,6 +470,25 @@ struct tester
          }
 
       }
+      //
+      // 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);
    }
 };