From f2821a0231aa85cc736e48acb165b93e708ba457 Mon Sep 17 00:00:00 2001
From: John Maddock <john@johnmaddock.co.uk>
Date: Mon, 1 Jul 2013 17:06:12 +0000
Subject: [PATCH] Fix left shift operator. Fixes #8741.

[SVN r84925]
---
 include/boost/multiprecision/cpp_int/bitwise.hpp | 12 ++----------
 test/test_cpp_int.cpp                            |  6 ++++++
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/include/boost/multiprecision/cpp_int/bitwise.hpp b/include/boost/multiprecision/cpp_int/bitwise.hpp
index 7df93181..95efacd7 100644
--- a/include/boost/multiprecision/cpp_int/bitwise.hpp
+++ b/include/boost/multiprecision/cpp_int/bitwise.hpp
@@ -229,12 +229,6 @@ inline typename enable_if_c<!is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBit
    limb_type offset = static_cast<limb_type>(s / cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::limb_bits);
    limb_type shift  = static_cast<limb_type>(s % cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::limb_bits);
 
-   /*
-   static const unsigned max_bits = max_bits<cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1> >::value;
-   static const unsigned max_limbs = max_bits / cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::limb_bits
-      + (max_bits % cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::limb_bits ? 1 : 0);
-   */
-
    unsigned ors = result.size();
    if((ors == 1) && (!*result.limbs()))
       return; // shifting zero yields zero.
@@ -244,8 +238,7 @@ inline typename enable_if_c<!is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBit
    rs += offset;
    result.resize(rs, rs);
    bool truncated = result.size() != rs;
-   if(truncated)
-      rs = result.size();
+
    typename cpp_int_backend<MinBits1, MaxBits1, SignType1, Checked1, Allocator1>::limb_pointer pr = result.limbs();
 
    if(offset > rs)
@@ -255,11 +248,10 @@ inline typename enable_if_c<!is_trivial_cpp_int<cpp_int_backend<MinBits1, MaxBit
       return;
    }
 
-   unsigned i = 0;
+   unsigned i = rs - result.size();
    if(shift)
    {
       // This code only works when shift is non-zero, otherwise we invoke undefined behaviour!
-      i = 0;
       if(!truncated)
       {
          if(rs > ors + offset)
diff --git a/test/test_cpp_int.cpp b/test/test_cpp_int.cpp
index 6e28001f..14f5bdac 100644
--- a/test/test_cpp_int.cpp
+++ b/test/test_cpp_int.cpp
@@ -173,6 +173,12 @@ struct tester
          {
             BOOST_CHECK_EQUAL(mpz_int(a << i).str(), test_type(a1 << i).str());
          }
+         else if(!is_checked_cpp_int<test_type>::value)
+         {
+            test_type t1(mpz_int(a << i).str());
+            test_type t2 = a1 << i;
+            BOOST_CHECK_EQUAL(t1, t2);
+         }
          BOOST_CHECK_EQUAL(mpz_int(a >> i).str(), test_type(a1 >> i).str());
       }
       // gcd/lcm