MINOR: tools: add very basic support for composite pointers

Very often we want to associate one or two flags to a pointer, to
put a type on it or whatever. This patch provides this in standard.h
in the form of a few inline functions which combine a void * pointer
with an int and return an unsigned long called a composite address.
The functions allow to individuall set, retrieve both the pointer and
the flags. This is very similar to what is used in ebtree in fact.

diff --git a/include/common/standard.h b/include/common/standard.h
index c4c5d64f175a74d4031b2f9886a63e03172e033b..14b0eba9b83e703ced20c96e4ae2475fdb2fbbc5 100644 (file)
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -776,4 +776,54 @@ static inline void shut_your_big_mouth_gcc(int r)
 /* same as strstr() but case-insensitive */
 const char *strnistr(const char *str1, int len_str1, const char *str2, int len_str2);
 
+
+/************************* Composite address manipulation *********************
+ * Composite addresses are simply unsigned long data in which the higher bits
+ * represent a pointer, and the two lower bits are flags. There are several
+ * places where we just want to associate one or two flags to a pointer (eg,
+ * to type it), and these functions permit this. The pointer is necessarily a
+ * 32-bit aligned pointer, as its two lower bits will be cleared and replaced
+ * with the flags.
+ *****************************************************************************/
+
+/* Masks the two lower bits of a composite address and converts it to a
+ * pointer. This is used to mix some bits with some aligned pointers to
+ * structs and to retrieve the original (32-bit aligned) pointer.
+ */
+static inline void *caddr_to_ptr(unsigned long caddr)
+{
+       return (void *)(caddr & ~3UL);
+}
+
+/* Only retrieves the two lower bits of a composite address. This is used to mix
+ * some bits with some aligned pointers to structs and to retrieve the original
+ * data (2 bits).
+ */
+static inline unsigned int caddr_to_data(unsigned long caddr)
+{
+       return (caddr & 3UL);
+}
+
+/* Combines the aligned pointer whose 2 lower bits will be masked with the bits
+ * from <data> to form a composite address. This is used to mix some bits with
+ * some aligned pointers to structs and to retrieve the original (32-bit aligned)
+ * pointer.
+ */
+static inline unsigned long caddr_from_ptr(void *ptr, unsigned int data)
+{
+       return (((unsigned long)ptr) & ~3UL) + (data & 3);
+}
+
+/* sets the 2 bits of <data> in the <caddr> composite address */
+static inline unsigned long caddr_set_flags(unsigned long caddr, unsigned int data)
+{
+       return caddr | (data & 3);
+}
+
+/* clears the 2 bits of <data> in the <caddr> composite address */
+static inline unsigned long caddr_clr_flags(unsigned long caddr, unsigned int data)
+{
+       return caddr & ~(unsigned long)(data & 3);
+}
+
 #endif /* _COMMON_STANDARD_H */