Crazy byteswapping thrift patches from david reiss
Reviewed By: ninjitsu
Test Plan: bswap64, holla holla
git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@665098 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/cpp/src/protocol/TBinaryProtocol.cpp b/lib/cpp/src/protocol/TBinaryProtocol.cpp
index 544ef88..5116e86 100644
--- a/lib/cpp/src/protocol/TBinaryProtocol.cpp
+++ b/lib/cpp/src/protocol/TBinaryProtocol.cpp
@@ -6,8 +6,50 @@
#include "TBinaryProtocol.h"
+#include <boost/static_assert.hpp>
+
using std::string;
+// Use this to get around strict aliasing rules.
+// For example, uint64_t i = bitwise_cast<uint64_t>(returns_double());
+// The most obvious implementation is to just cast a pointer,
+// but that doesn't work.
+// For a pretty in-depth explanation of the problem, see
+// http://www.cellperformance.com/mike_acton/2006/06/ (...)
+// understanding_strict_aliasing.html
+template <typename To, typename From>
+static inline To bitwise_cast(From from) {
+ BOOST_STATIC_ASSERT(sizeof(From) == sizeof(To));
+
+ // BAD!!! These are all broken with -O2.
+ //return *reinterpret_cast<To*>(&from); // BAD!!!
+ //return *static_cast<To*>(static_cast<void*>(&from)); // BAD!!!
+ //return *(To*)(void*)&from; // BAD!!!
+
+ // Super clean and paritally blessed by section 3.9 of the standard.
+ //unsigned char c[sizeof(from)];
+ //memcpy(c, &from, sizeof(from));
+ //To to;
+ //memcpy(&to, c, sizeof(c));
+ //return to;
+
+ // Slightly more questionable.
+ // Same code emitted by GCC.
+ //To to;
+ //memcpy(&to, &from, sizeof(from));
+ //return to;
+
+ // Technically undefined, but almost universally supported,
+ // and the most efficient implementation.
+ union {
+ From f;
+ To t;
+ } u;
+ u.f = from;
+ return u.t;
+}
+
+
namespace facebook { namespace thrift { namespace protocol {
uint32_t TBinaryProtocol::writeMessageBegin(const std::string& name,
@@ -113,17 +155,12 @@
}
uint32_t TBinaryProtocol::writeDouble(const double dub) {
- uint8_t b[8];
- uint8_t* d = (uint8_t*)&dub;
- b[0] = d[7];
- b[1] = d[6];
- b[2] = d[5];
- b[3] = d[4];
- b[4] = d[3];
- b[5] = d[2];
- b[6] = d[1];
- b[7] = d[0];
- trans_->write((uint8_t*)b, 8);
+ BOOST_STATIC_ASSERT(sizeof(double) == sizeof(uint64_t));
+ BOOST_STATIC_ASSERT(std::numeric_limits<double>::is_iec559);
+
+ uint64_t bits = bitwise_cast<uint64_t>(dub);
+ bits = htonll(bits);
+ trans_->write((uint8_t*)&bits, 8);
return 8;
}
@@ -291,18 +328,15 @@
}
uint32_t TBinaryProtocol::readDouble(double& dub) {
+ BOOST_STATIC_ASSERT(sizeof(double) == sizeof(uint64_t));
+ BOOST_STATIC_ASSERT(std::numeric_limits<double>::is_iec559);
+
+ uint64_t bits;
uint8_t b[8];
- uint8_t d[8];
trans_->readAll(b, 8);
- d[0] = b[7];
- d[1] = b[6];
- d[2] = b[5];
- d[3] = b[4];
- d[4] = b[3];
- d[5] = b[2];
- d[6] = b[1];
- d[7] = b[0];
- dub = *(double*)d;
+ bits = *(uint64_t*)b;
+ bits = ntohll(bits);
+ dub = bitwise_cast<double>(bits);
return 8;
}