Author: stefan2
Date: Mon Jul 29 22:46:22 2013
New Revision: 1508222
URL: http://svn.apache.org/r1508222
Log:
Depending on the #include order of svn_private_config.h vs.
svn_hash.h, SVN_HAS_DUNDER_BUILTINS may not be defined when
the svn_hash_gets macro is being parsed.
Generate a compiler warning when svn_hash.h gets #included
before svn_private_config.h.
* subversion/include/svn_hash.h
(SVN_HAS_DUNDER_BUILTINS): disable optimization when undefined
(svn_hash_gets): extend commentary
Modified:
subversion/trunk/subversion/include/svn_hash.h
Modified: subversion/trunk/subversion/include/svn_hash.h
URL:
http://svn.apache.org/viewvc/subversion/trunk/subversion/include/svn_hash.h?rev=1508222&r1=1508221&r2=1508222&view=diff
==============================================================================
--- subversion/trunk/subversion/include/svn_hash.h (original)
+++ subversion/trunk/subversion/include/svn_hash.h Mon Jul 29 22:46:22 2013
@@ -37,7 +37,6 @@
#include "svn_types.h"
#include "svn_io.h" /* for svn_stream_t */
-
#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */
@@ -240,19 +239,32 @@ svn_hash_from_cstring_keys(apr_hash_t **
const apr_array_header_t *keys,
apr_pool_t *pool);
+/* Used by the svn_hash_gets macro.
+ * Make sure you either defined it before including this header or not
+ * at all.
+ */
+#if !defined(SVN_HAS_DUNDER_BUILTINS)
+/* If you define it elsewhere to generate better code, the definition
+ * below will usually generate a compiler warning if your definition is
+ * being encountered _after_ #including this header.
+ */
+#define SVN_HAS_DUNDER_BUILTINS 0
+#endif
+
/** Shortcut for apr_hash_get() with a const char * key.
*
* @since New in 1.8.
*/
#if SVN_HAS_DUNDER_BUILTINS
-/* We have two use-cases:
+/* We have three use-cases:
1. (common) KEY is a string literal.
- 2. (rare) KEY is the result of an expensive function call.
- For the former, we want to evaluate the string length at compile time. (We
- use strlen(), which gets optimized to a constant.) For the latter, however,
- we want to avoid having the macro multiply-evaluate KEY. So, if our
- compiler is smart enough (that includes at least gcc and clang), we use
- __builtin_constant_p() to have our cake and eat it too: */
+ 2. (less common) KEY is a const char*.
+ 3. (rare) KEY is the result of an expensive function call.
+ For the first, we want to evaluate the string length at compile time.
+ (We use strlen(), which gets optimized to a constant.) For the other
+ two, however, we want to avoid having the macro multiply-evaluate KEY.
+ So, if our compiler is smart enough (that includes at least gcc and
+ clang), we use __builtin_constant_p() to have our cake and eat it too: */
# define svn_hash_gets(ht, key) \
apr_hash_get(ht, key, \
__builtin_constant_p(strlen(key)) \
