[Boost-bugs] [Boost C++ Libraries] #13223: Undefined behavior inside assign_bits while importing data to cpp_int

Subject: [Boost-bugs] [Boost C++ Libraries] #13223: Undefined behavior inside assign_bits while importing data to cpp_int
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2017-09-21 12:40:13

#13223: Undefined behavior inside assign_bits while importing data to cpp_int
--------------------------------+----------------------------
 Reporter:  Dennis <yowidin@…>  |      Owner:  John Maddock
     Type:  Bugs                |     Status:  new
Milestone:  To Be Determined    |  Component:  multiprecision
  Version:  Boost 1.64.0        |   Severity:  Problem
 Keywords:                      |
--------------------------------+----------------------------
 Trying to import bits from unsigned char array results in undefined
 behavior as reported by Clang.

 Minimal example:
 {{{#!cpp
 #include <iostream>
 #include <cstdint>

 #include <boost/multiprecision/cpp_int.hpp>

 using mp_int_t = boost::multiprecision::int128_t;
 using source_t = std::vector<std::uint8_t>;

 int main() {
    source_t src(16, 0);

    mp_int_t result;
    import_bits(result, src.begin(), src.end(), 0, false);

    return 0;
 }
 }}}

 Compile command:

 {{{#!bash
 clang++ main.cpp \
    -g -O1 -fsanitize=undefined -fno-omit-frame-pointer \
    -fno-optimize-sibling-calls -std=c++11 -o main
 }}}

 Runtime output:
 {{{
 boost/multiprecision/cpp_int/import_export.hpp:64:21: runtime error: shift
 exponent 128 is too large for 8-bit type 'unsigned char'
 }}}

 Environment information:

 - Ubuntu 16.04 LTS 64bit
 - Tested with Clang 3.8.0 and Clang 5.0.0

-- 
Ticket URL: <https://svn.boost.org/trac10/boost/ticket/13223>
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