Fixing issues with alignment, undefined behaviour and endianness in the...

Fixing issues with alignment, undefined behaviour and endianness in the FieldTrial::HashName function. I also added new functions to base that convert from host order to little endian.

BUG=123230FieldTrialTest.HashName
TEST=FieldTrialTest.HashName


Review URL: http://codereview.chromium.org/10088001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@132404 0039d316-1c4b-4281-b951-d872f2087c98

base/metrics/field_trial.cc

@@ -10,6 +10,7 @@
 #include "base/sha1.h"
 #include "base/stringprintf.h"
 #include "base/string_util.h"
+#include "base/sys_byteorder.h"
 #include "base/utf_string_conversions.h"
 
 namespace base {
@@ -212,13 +213,14 @@ uint32 FieldTrial::HashName(const std::string& name) {
                 sha1_hash);
 
   COMPILE_ASSERT(sizeof(uint32) < sizeof(sha1_hash), need_more_data);
-  uint32* bits = reinterpret_cast<uint32*>(&sha1_hash[0]);
+  uint32 bits;
+  memcpy(&bits, sha1_hash, sizeof(bits));
 
   // We only DCHECK, since this should not happen because the registration
   // of the experiment on the server should have already warn the developer.
   // If this ever happen, we'll ignore this experiment/group when reporting.
-  DCHECK(*bits != kReservedHashValue);
-  return *bits;
+  DCHECK(bits != kReservedHashValue);
+  return base::ByteSwapToLE32(bits);
 }
 
 //------------------------------------------------------------------------------

base/sys_byteorder.h

@@ -69,6 +69,30 @@ inline uint64 ByteSwap(uint64 x) {
 #endif
 }
 
+// Converts the bytes in |x| from host order (endianness) to little endian, and
+// returns the result.
+inline uint16 ByteSwapToLE16(uint16 x) {
+#if defined(ARCH_CPU_LITTLE_ENDIAN)
+  return x;
+#else
+  return ByteSwap(x);
+#endif
+}
+inline uint32 ByteSwapToLE32(uint32 x) {
+#if defined(ARCH_CPU_LITTLE_ENDIAN)
+  return x;
+#else
+  return ByteSwap(x);
+#endif
+}
+inline uint64 ByteSwapToLE64(uint64 x) {
+#if defined(ARCH_CPU_LITTLE_ENDIAN)
+  return x;
+#else
+  return ByteSwap(x);
+#endif
+}
+
 // Converts the bytes in |x| from network to host order (endianness), and
 // returns the result.
 inline uint16 NetToHost16(uint16 x) {