[THRIFT-1666] htonll usage in TBinaryProtocol.tcc generates warning with MSVC2010

• Type: Bug
• Status: Closed
• Priority: Trivial
• Resolution: Fixed
• Affects Version/s: 0.8
• Fix Version/s: 0.9.1
• Component/s: C++ - Library
• Labels: msvc warning

Environment

Microsoft Visual Studio 10.0 (2010).

• Patch Info: Patch Available
• Assignee: Jake Farrell
• Reporter: Brandon Streiff
• Created: 31/Jul/12 14:44
• Updated: 08/Jun/13 18:14
• Resolved: 08/Jun/13 18:14

Description

When using the Thrift library I get warnings like the following:

thrift\protocol\TBinaryProtocol.tcc(161): warning C4244: 'argument' : conversion from 'const int64_t' to 'u_long', possible loss of data

This is because TBinaryProtocol.tcc uses htonll on an incoming const int64_t parameter to perform byteswapping, and in TProtocol.h htonll gets defined like so:

#  define htonll(n) ( (((uint64_t)htonl(n)) << 32) + htonl(n >> 32) )

htonl() takes a u_long parameter, so MSVC warns when passing in a uint64_t parameter because it truncates. This could have been fixed by casting the input parameters, but there's also a nice handy _byteswap_uint64() function in the MSVC CRT that we can use without all of the shifting that calling ntohl twice requires.

Patch follows:

--- a\lib\cpp\src\protocol\TProtocol.h 31 Jul 2012  9:18:02 AM
+++ b\lib\cpp\src\protocol\TProtocol.h 31 Jul 2012  9:19:48 AM
@@ -127,140 +127,143 @@
 #  define letohll(n) (n)
 # if defined(__GNUC__) && defined(__GLIBC__)
 #  include <byteswap.h>
 #  define ntohll(n) bswap_64(n)
 #  define htonll(n) bswap_64(n)
-# else /* GNUC & GLIBC */
+# elif defined(_MSC_VER) /* Microsoft Visual C++ */
+#  define ntohll(n) ( _byteswap_uint64((uint64_t)n) )
+#  define htonll(n) ( _byteswap_uint64((uint64_t)n) )
+# else /* Not GNUC/GLIBC or MSVC */
 #  define ntohll(n) ( (((uint64_t)ntohl(n)) << 32) + ntohl(n >> 32) )
 #  define htonll(n) ( (((uint64_t)htonl(n)) << 32) + htonl(n >> 32) )
-# endif /* GNUC & GLIBC */
+# endif /* GNUC/GLIBC or MSVC or something else */
 #else /* __BYTE_ORDER */
 # error "Can't define htonll or ntohll!"
 #endif

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