--- libecb/ecb.h	2011/07/20 00:38:30	1.54
+++ libecb/ecb.h	2011/08/04 06:38:35	1.59
@@ -50,7 +50,7 @@
 
 /* many compilers define _GNUC_ to some versions but then only implement
  * what their idiot authors think are the "more important" extensions,
- * causing enourmous grief in return for some better fake benchmark numbers.
+ * causing enormous grief in return for some better fake benchmark numbers.
  * or so.
  * we try to detect these and simply assume they are not gcc - if they have
  * an issue with that they should have done it right in the first place.
@@ -65,16 +65,25 @@
 
 /*****************************************************************************/
 
+/* ECB_NO_THREADS - ecb is not used by multiple threads, ever */
+/* ECB_NO_SMP     - ecb might be used in multiple threads, but only on a single cpu */
+
+#if ECB_NO_THREADS || ECB_NO_SMP
+  #define ECB_MEMORY_FENCE         do { } while (0)
+  #define ECB_MEMORY_FENCE_ACQUIRE do { } while (0)
+  #define ECB_MEMORY_FENCE_RELEASE do { } while (0)
+#endif
+
 #ifndef ECB_MEMORY_FENCE
   #if ECB_GCC_VERSION(2,5)
     #if __x86
       #define ECB_MEMORY_FENCE         __asm__ __volatile__ ("lock; orb $0, -1(%%esp)" : : : "memory")
-      #define ECB_MEMORY_FENCE_ACQUIRE ECB_MEMORY_FENCE
-      #define ECB_MEMORY_FENCE_RELEASE ECB_MEMORY_FENCE /* better be safe than sorry */
+      #define ECB_MEMORY_FENCE_ACQUIRE ECB_MEMORY_FENCE /* non-lock xchg might be enough */
+      #define ECB_MEMORY_FENCE_RELEASE do { } while (0) /* unlikely to change in future cpus */
     #elif __amd64
       #define ECB_MEMORY_FENCE         __asm__ __volatile__ ("mfence" : : : "memory")
       #define ECB_MEMORY_FENCE_ACQUIRE __asm__ __volatile__ ("lfence" : : : "memory")
-      #define ECB_MEMORY_FENCE_RELEASE __asm__ __volatile__ ("sfence")
+      #define ECB_MEMORY_FENCE_RELEASE __asm__ __volatile__ ("sfence") /* play safe - not needed in any current cpu */
     #endif
   #endif
 #endif
@@ -84,18 +93,27 @@
     #define ECB_MEMORY_FENCE         __sync_synchronize ()
     #define ECB_MEMORY_FENCE_ACQUIRE ({ char dummy = 0; __sync_lock_test_and_set (&dummy, 1); })
     #define ECB_MEMORY_FENCE_RELEASE ({ char dummy = 1; __sync_lock_release      (&dummy   ); })
-  #elif _MSC_VER >= 1400
-    #define ECB_MEMORY_FENCE         do { } while (0)
-    #define ECB_MEMORY_FENCE_ACQUIRE ECB_MEMORY_FENCE
-    #define ECB_MEMORY_FENCE_RELEASE ECB_MEMORY_FENCE
-  #elif defined(_WIN32) && defined(MemoryBarrier)
-    #define ECB_MEMORY_FENCE         MemoryBarrier ()
+  #elif _MSC_VER >= 1400 /* VC++ 2005 */
+    #pragma intrinsic(_ReadBarrier,_WriteBarrier,_ReadWriteBarrier)
+    #define ECB_MEMORY_FENCE         _ReadWriteBarrier ()
+    #define ECB_MEMORY_FENCE_ACQUIRE _ReadWriteBarrier () /* according to msdn, _ReadBarrier is not a load fence */
+    #define ECB_MEMORY_FENCE_RELEASE _WriteBarrier ()
+  #elif defined(_WIN32)
+    #include <WinNT.h>
+    #define ECB_MEMORY_FENCE         MemoryBarrier () /* actually just xchg on x86... scary */
     #define ECB_MEMORY_FENCE_ACQUIRE ECB_MEMORY_FENCE
     #define ECB_MEMORY_FENCE_RELEASE ECB_MEMORY_FENCE
   #endif
 #endif
 
 #ifndef ECB_MEMORY_FENCE
+  /*
+   * if you get undefined symbol references to pthread_mutex_lock,
+   * or failure to find pthread.h, then you should implement
+   * the ECB_MEMORY_FENCE operations for your cpu/compiler
+   * OR provide pthread.h and link against the posix thread library
+   * of your system.
+   */
   #include <pthread.h>
 
   static pthread_mutex_t ecb_mf_lock = PTHREAD_MUTEX_INITIALIZER;
@@ -234,9 +252,6 @@
     return x >> 24;
   }
 
-  /* you have the choice beetween something with a table lookup, */
-  /* something using lots of bit arithmetic and a simple loop */
-  /* we went for the loop */
   ecb_function_ int ecb_ld32 (uint32_t x) ecb_const;
   ecb_function_ int ecb_ld32 (uint32_t x)
   {