From d7917b9c348de3a83eee9d1850974a66cc6b4b1b Mon Sep 17 00:00:00 2001
From: Steven Strand <steven.strand@block.one>
Date: Fri, 1 Feb 2019 16:02:46 -0500
Subject: [PATCH] fix issue #400 extract signed_int from datastream

---
 libraries/eosiolib/varint.hpp | 11 ++++-------
 tests/CMakeLists.txt          |  1 +
 tests/unit/CMakeLists.txt     |  1 +
 tests/unit/varint_tests.cpp   | 28 ++++++++++++++++++++++++++++
 4 files changed, 34 insertions(+), 7 deletions(-)
 create mode 100644 tests/unit/varint_tests.cpp

diff --git a/libraries/eosiolib/varint.hpp b/libraries/eosiolib/varint.hpp
index a89cb5dde41..57966442d83 100644
--- a/libraries/eosiolib/varint.hpp
+++ b/libraries/eosiolib/varint.hpp
@@ -4,7 +4,6 @@
  */
 #pragma once
 
-
 /**
  * @defgroup varint Variable Length Integer Type
  * @brief Defines variable length integer type which provides more efficient serialization
@@ -406,8 +405,8 @@ struct signed_int {
      */
     template<typename DataStream>
     friend DataStream& operator << ( DataStream& ds, const signed_int& v ){
-      uint32_t val = uint32_t((v.value<<1) ^ (v.value>>31));
-      do {
+      uint32_t val = uint32_t((v.value<<1) ^ (v.value>>31));    //apply zigzag encoding
+      do {                                                      //store 7 bit chunks
          uint8_t b = uint8_t(val) & 0x7f;
          val >>= 7;
          b |= ((val > 0) << 7);
@@ -427,14 +426,12 @@ struct signed_int {
     template<typename DataStream>
     friend DataStream& operator >> ( DataStream& ds, signed_int& vi ){
       uint32_t v = 0; char b = 0; int by = 0;
-      do {
+      do {                                                      //read 7 bit chunks
          ds.get(b);
          v |= uint32_t(uint8_t(b) & 0x7f) << by;
          by += 7;
       } while( uint8_t(b) & 0x80 );
-      vi.value = ((v>>1) ^ (v>>31)) + (v&0x01);
-      vi.value = v&0x01 ? vi.value : -vi.value;
-      vi.value = -vi.value;
+      vi.value= (v>>1) ^ -(v&1);                                //reverse zigzag encoding
       return ds;
     }
 };
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index b03ec429296..3e9c5a4db66 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -2,6 +2,7 @@ add_test(name_tests ${CMAKE_BINARY_DIR}/tests/unit/name_tests)
 add_test(rope_tests ${CMAKE_BINARY_DIR}/tests/unit/rope_tests)
 add_test(print_tests ${CMAKE_BINARY_DIR}/tests/unit/print_tests)
 add_test(system_tests ${CMAKE_BINARY_DIR}/tests/unit/system_tests)
+add_test(varint_tests ${CMAKE_BINARY_DIR}/tests/unit/varint_tests)
 if (eosio_FOUND)
    add_test(integration_tests ${CMAKE_BINARY_DIR}/tests/integration/integration_tests)
 endif()
diff --git a/tests/unit/CMakeLists.txt b/tests/unit/CMakeLists.txt
index 3ea8443c893..6d46ab565c4 100644
--- a/tests/unit/CMakeLists.txt
+++ b/tests/unit/CMakeLists.txt
@@ -5,5 +5,6 @@ add_native_executable(name_tests name_tests.cpp)
 add_native_executable(system_tests system_tests.cpp)
 add_native_executable(rope_tests rope_tests.cpp)
 add_native_executable(print_tests print_tests.cpp)
+add_native_executable(varint_tests varint_tests.cpp)
 
 add_subdirectory(test_contracts)
diff --git a/tests/unit/varint_tests.cpp b/tests/unit/varint_tests.cpp
new file mode 100644
index 00000000000..8868e7cb51c
--- /dev/null
+++ b/tests/unit/varint_tests.cpp
@@ -0,0 +1,28 @@
+#include <eosiolib/eosio.hpp>
+#include <eosio/native/tester.hpp>
+
+using namespace eosio::native;
+using namespace eosio;
+
+EOSIO_TEST_BEGIN(signed_int_test)   //test datastream insert/extract signed_int
+   //silence_output(true);
+
+   char buffer[32];
+   datastream ds(buffer,32);
+   signed_int a(44), b((1<<30)+2), c(-35), d(-(1<<30)-2);   //small +, small -, large +, large -
+   ds << a << b << c << d;
+   ds.seekp(0);
+   signed_int aa, bb, cc, dd;
+   ds >> aa >> bb >> cc >> dd;
+   char* errmess= "signed_int datastream extract fails";
+   check(a.value==aa.value,errmess);
+   check(b.value==bb.value,errmess);
+   check(c.value==cc.value,errmess);
+   check(d.value==dd.value,errmess);
+   silence_output(false);
+EOSIO_TEST_END
+
+int main(int argc, char** argv) {
+   EOSIO_TEST(signed_int_test);
+   return has_failed();
+}