diff --git a/ChangeLog b/ChangeLog
index 73f2204..ecd0883 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,11 +1,15 @@
-2017-11-21 Kim Walisch  <kim.walisch@gmail.com>
+2017-11-25 Kim Walisch  <kim.walisch@gmail.com>
 
-  Version 1.2 work in progress.
+  Version 1.2 released.
 
-  * Reduce input limit from 10^20 to 2^64-1 to prevent
-    128-bit integer overflows in S1(x).
+  This version fixes an integer overflow in primesum 128-bit
+  and speeds up primesum 256-bit by up to 30% due to replacing the
+  Boost multiprecision library with my own highly optimized
+  int256_t type.
+
+  * int256_t.hpp: New 256-bit signed integer type.
   * Fix 128-bit integer overflow in phi_sum.cpp.
-  * primesum 256-bit runs 10% faster.
+  * Reduce input limit from 10^20 to 2^64-1 in primesum 128-bit.
   * CMakeLists.txt: Silence OpenMP warning.
   * README.md: Update build instructions.
   * .travis.yml: Update to Ubuntu 14.
diff --git a/lib/primesieve/.gitignore b/lib/primesieve/.gitignore
new file mode 100644
index 0000000..7a845a9
--- /dev/null
+++ b/lib/primesieve/.gitignore
@@ -0,0 +1,25 @@
+.*
+*~
+!/.gitignore
+!/.travis.yml
+*.exe
+*.tar.gz
+*.zip
+*.obj
+*.lib
+*.o
+*.pc
+*.dSYM
+CMakeCache.txt
+CMakeFiles
+CMakeScripts
+Makefile
+cmake_install.cmake
+install_manifest.txt
+CTestTestfile.cmake
+/primesieve*
+/libprimesieve*
+doc/Doxyfile
+doc/html
+doc/latex
+build
diff --git a/lib/primesieve/.travis.yml b/lib/primesieve/.travis.yml
new file mode 100644
index 0000000..8d23a84
--- /dev/null
+++ b/lib/primesieve/.travis.yml
@@ -0,0 +1,63 @@
+# Test configuration for Travis CI. See <https://travis-ci.org/>.
+language: cpp
+
+branches:
+  except:
+    - gh-pages
+
+compiler:
+  - gcc
+  - clang
+
+os:
+  - linux
+
+addons:
+  apt:
+    sources:
+    - ubuntu-toolchain-r-test
+    packages:
+    - gcc-4.9
+    - g++-4.9
+
+install:
+  - sudo apt-get install -y ninja-build cppcheck doxygen help2man texlive texlive-latex-extra graphviz libqt4-dev qt4-qmake valgrind
+  - wget --no-check-certificate http://cmake.org/files/v3.1/cmake-3.1.3-Linux-x86_64.tar.gz
+  - tar -xzf cmake-3.1.3-Linux-x86_64.tar.gz
+  - export CXXFLAGS="-Wall -Wextra -Werror -Wno-long-long -pedantic -O2"
+  - export PATH=$PWD/cmake-3.1.3-Linux-x86_64/bin:$PATH
+  - if [ "$CXX" = "g++" ]; then export CXX="g++-4.9"; fi
+  - if [ "$CC" = "gcc" ]; then export CC="gcc-4.9"; fi
+
+script:
+  # 1) Build using GNU make
+  - mkdir build
+  - cd build
+  - cmake -DBUILD_EXAMPLES=ON -DBUILD_TESTS=ON -DBUILD_DOC=ON -DCMAKE_INSTALL_PREFIX=$(pwd) ..
+  - make -j4
+  - make doc >/dev/null
+  - make install
+  - cd ..
+  - rm -rf build
+  # 2) Build primesieve GUI app
+  - cd src/gui
+  - qmake QMAKE_CXX=$CXX QMAKE_CC=$CC
+  - make -j4
+  - cd ../..
+  # 3) Build using ninja
+  - mkdir build
+  - cd build
+  - cmake -GNinja -DBUILD_EXAMPLES=ON -DBUILD_TESTS=ON -DBUILD_DOC=ON ..
+  - ninja
+  - ninja doc >/dev/null
+  # 4) Run integration tests
+  - ninja test
+  - test/cpu_info
+  - test/atomic
+  - cd ..
+  # 5) Test using valgrind
+  - $CXX -Iinclude -O2 -std=c++11 -g examples/cpp/nth_prime.cpp -o nth_prime build/libprimesieve.a -lpthread
+  - valgrind --error-exitcode=1 ./nth_prime 500000000
+  # 6) Test using cppcheck
+  - rm -rf build
+  - cppcheck . -q --error-exitcode=1 -icmake-3.1.3-Linux-x86_64 -iexamples/cpp/prev_prime.cpp -iexamples/cpp/primesieve_iterator.cpp -itest/next_prime1.cpp -itest/prev_prime1.cpp
diff --git a/lib/primesieve/CMakeLists.txt b/lib/primesieve/CMakeLists.txt
index dba7763..606dc4d 100644
--- a/lib/primesieve/CMakeLists.txt
+++ b/lib/primesieve/CMakeLists.txt
@@ -59,31 +59,49 @@ endif()
 
 # Check if libatomic is needed #######################################
 
+include(CMakePushCheckState)
 include(CheckCXXSourceCompiles)
 
-set(CMAKE_OLD_FLAGS ${CMAKE_REQUIRED_FLAGS})
+cmake_push_check_state()
 set(CMAKE_REQUIRED_FLAGS ${CMAKE_CXX11_STANDARD_COMPILE_OPTION})
 
 check_cxx_source_compiles("
     #include <atomic>
+    #include <stdint.h>
     int main() {
-        std::atomic<int> x;
+        std::atomic<int64_t> x;
         x = 1;
         x--;
-        return x;
+        return (int) x;
     }"
-    have_atomic)
+    atomic64)
 
-set(CMAKE_REQUIRED_FLAGS ${CMAKE_OLD_FLAGS})
+if(NOT atomic64)
+    find_library(ATOMIC NAMES atomic libatomic.so.1)
 
-if(NOT have_atomic)
-    find_library(ATOMIC NAMES atomic libatomic.so libatomic.so.1)
     if(ATOMIC)
         set(LIBATOMIC ${ATOMIC})
-        message(STATUS "Found libatomic: TRUE")
+        message(STATUS "Found libatomic: ${LIBATOMIC}")
+    else()
+        check_cxx_source_compiles("
+            #include <atomic>
+            #include <stdint.h>
+            int main() {
+                std::atomic<int32_t> x;
+                x = 1;
+                x--;
+                return (int) x;
+            }"
+            atomic32)
+
+        if(atomic32)
+            message(FATAL_ERROR "Failed to find libatomic!")
+        endif()
     endif()
 endif()
 
+cmake_pop_check_state()
+
 # libprimesieve ######################################################
 
 add_library(libprimesieve ${LIB_SRC})
diff --git a/lib/primesieve/ChangeLog b/lib/primesieve/ChangeLog
index a5f7943..4ccda37 100644
--- a/lib/primesieve/ChangeLog
+++ b/lib/primesieve/ChangeLog
@@ -1,3 +1,8 @@
+Changes in version 6.4, 25/11/2017
+==================================
+
+ * CMakeLists.txt: Fix libatomic detection.
+
 Changes in version 6.3, 12/11/2017
 ==================================